Table of Contents

  1. General
  2. Erection of Switchboards at Site
  3. Technical Information from Vendor
  4. Design
  5. Components
  6. Tools
  7. Spare Parts
  8. Inspection and Tests
  9. Client's Additional Requirements to Company's Specification/Requisition
  10. Deviations from Specification and Requistion
  11. Approved Vendor Deviations from Specification and Requisition


1. General

1.1 Description

This specification defines the minimum technical requirements for the design, the fabrication and the testing of completely assembled metal-enclosed low voltage switchboards of the draw-out type, for service voltages up to 1 kV and for installation in oil refineries, chemical plants, and other industrial installations.

Additional information for each individual case will be given in the relevant requisition.

1.2 Standards

In addition to this specification, the switchboards shall be designed and built in accordance with the latest issues of the standards mentioned in the requisition, the relevant IEC standards and the latest codes and regulations of the country of final installation.

1.3 Certificate

The vendor of the switchboards shall supply, together with his quotation, a copy of a type-test certificate from a recognized testing laboratory.

1.4 Site Conditions

The switchboards will be installed indoors in a nonhazardous atmosphere with an ambient temperature between -10C up to 35C an altitude not exceeding 1000 m.

1.5 Conflicting Requirements

In case of conflict between the conditions and the documents mentioned above or between them and this specification, the severest requirements shall govern. Purchaser will not be obliged to check vendor’s documents such as quotations, order confirmations, drawings, etc. Purchaser will review these in principle only.

It will remain vendor’s responsibility to fabricate the switchboards in accordance with this specification in a fully functional and workmanlike manner.

A deviation from this specification will only be acceptable if vendor has specified in his quotation under the heading “Deviations from Specification” the requirements he cannot meet and if Company has accepted this deviation in writing before order award, or has confirmed acceptance in the purchase order.

If deviations will not be specified, purchaser will interpret this as confirmation that vendor will comply with this specification. Any extra costs arising subsequently as a result shall be borne by the vendor.

2. Erection of Switchboards at Site

Unless otherwise specified in the requisition, switchboards will be erected and tested at site by others without supervision by the switchboard supplier.

3. Technical Information from Vendor

3.1 The following information shall be supplied together with the quotation:

3.1.1 The fundamental outline drawings, front layouts.

3.1.2 The approximate weights of the switchboards.

3.1.3 A copy of the type-test certificate.

3.1.4 Complete sets of vendor’s leaflets and brochures with all technical information on the quoted material.

3.1.5 Vendor’s confirmation that rear access is not required.

3.1.6 The maximum permissible and the applied loading factor of the outgoing vertical sections.

3.1.7 The names of sub-suppliers for the following equipment:

- Circuit breakers

- Fuses

- Contactors and the auxiliary relays

- Thermal relays

- Switches and circuit breakers for outgoing circuits

- Secondary protection relays

- Bus ducts (if any)

- EF protection relays

- MCB’s applied.

3.2 The following drawings shall be submitted for approval after order award:

3.2.1 The final dimensions and weights of the switchboards.

(Same for all other panels forming part of the order).

3.2.2 The information necessary to enable Company’s Civil Department to design the station floor.

3.2.3 The heat dissipation per switchboard and other panels for the design of the HVAC installation.

3.2.4 The location of the bus ducts or incoming feeder cables.

3.2.5 The size and the location of all outgoing circuits including spares and spaces in a front layout for each switchboard or panel.

3.3 Drawings Necessary for Construction

Within 2 weeks after the drawings as per item 3.2 have been returned, vendor shall submit the corrected drawings to purchaser.

3.4 Instructions

8 weeks before the delivery date, as indicated in the order, vendor shall supply the instructions for erection, installation, testing, operating and maintenance.

4. Design

4.1 Structure

4.1.1 The switchboard shall be designed so as to ensure safety during operation, inspection, connection of cables, relocation of outgoing circuits and maintenance, with the busbar system energized and without taking any special precautions.

4.1.2 The switchboard shall consist of vertical sections joined together so as to form a complete switchboard. Each vertical section shall be completely metal-enclosed.

4.1.3 A construction for which rear access is necessary will not be acceptable, unless specifieds otherwise in the requisition.

4.1.4 The switchboard shall be free-standing on the floor and not need external supports. Provisions shall be made to weld or to bolt the switchboard structure to a beam imbedded in the substation floor.

4.1.5 Removable lifting lugs shall be provided to permit easy transport. Removal of a lug eye may never result in an opening in the enclosure.

4.1.6 The switchboard shall be extendable at both ends by means of the addition of vertical sections of an identical construction. If shall be possible to perform this work without interference with the existing sections and drilling holes in the existing busbar system.

4.1.7 All vertical sections shall be identical and be interchangeable. They shall be arranged so as to accommodate any of the specified units in any combination from top to bottom, taking into account the permissible loading factor. The design shall permit future exchange of units by purchaser without cutting, welding or major structural changes. The exchange shall be possible in a save manner with the busbar system live the nonaffected units in operation, so that parts or tools cannot come into contact with live parts.

Unused connections to the vertical busbars shall be protected so that even the smallest wire cannot enter the opening.

4.1.8 The sections arranged for the busduct connection shall be supplied complete with a mating sheet metal busduct hood and the section shall be adequately reinforced to carry the busduct weight imposed on it.

4.1.9 All joints and connections shall be made with high-tensile strength steel bolts, nuts and washers securing the connections against loosening. Connections with self-tapping screws will not be allowed. Connections with thread-making bolts will be acceptable provided the threaded connections can be reused, giving the same strength.

4.1.10 All vertical sections shall be bolted together using a soft neoprene or identical packing rim between the frameworks to avoid openings between the sections. Soft neoprene rims shall also be provided to prevent penetration of dust through doors, covers, etc.

4.1.11 Each vertical sections shall have sufficient space at the bottom of the section to allow for proper connection of the cables for the lowest unit.

4.1.12 All units installed in vertical sections shall have the same mechanical features.

4.1.13 All doors shall be provided with a stop preventing them from slamming against an adjacent compartment. The door shall be provided with an interlock with the main incoming switch of the unit to prevent the door from completely opened. The door may move slightly but at least the IP 20 requirement shall be maintained. Moving the door shall not result in a movement of the unit.

Parts of the control circuitry such as switches, pushbuttons, indicating lights and measuring devices shall not be installed on the door, but on the draw-out unit only.

Components may be mounted on the doors of fixed mounted equipment or circuit breaker compartments. However, the door shall be adequately reinforced to carry the extra weight. All live parts and terminals connected shall be effectively protected against accidental contact with shrouds and/or covers.

Hinges shall not be considered as PE conductor; the doors shall be grounded by means of bare stranded copper wire.

Only if specified, a device to override the door interlock shall be provided. This shall be required to perform an infrared scanning check on the current-carrying paths of a unit.

Swivel-type doors lock(s) shall be provided; they shall be keyoperated for those compartment doors access to live parts is possible, if the installed equipment or material does not have an integral degree of protection of IP 20.

Protecting covers will not be considered as an integral protection of materials.

4.1.14 When the main power switch of a draw-out unit is closed, it shall not be possible to open the door or cover and/or to move the unit.

The main power switch of fixed mounted units shall be open and all fuses be “dead” before the door or cover can be opened. The live side of the switch up to and including the connections to the busbars shall be protected at least IP 4X; separations between phases and phase to neutral shall be provided.

4.1.15 Functional Testing of Outgoing Circuits

Testing of Draw-out Units

The following options exist and have preference in the ascending sequence:

- Special automatic test position, where the main power path to the consumer is completely interrupted and the unit itself is not accessible for the tester.

- Testing of the draw-out unit outside the switchgear using a special test cabinet, with all required control voltages supplied through a safety transformer so that the first earth fault cannot harm the tester. The test unit shall be provided with optimum electrical protection and be constructed so that two hands are necessary for functional testing using two differently located push buttons.

- A test position inside the compartment where the connection between the unit and the consumer is interrupted by removing the main power path fuses or other links in the power path.

Testing of Fixed Mounted Units

The main power supply of fixed mounted units shall be disconnected before the door or cover will be opened.

In order to be able to test the outgoing circuits functionally, facilities shall be available for AC and DC operated control circuits, using a key-locked test switching arrangement, in combination with auxiliary contacts of the main power switch, which are preventing energization of the main power path. If the test control power is connected to the control circuit, it shall be impossible to close the main power switch; the contactor in the circuit shall be tripped before the main power switch will be closed.

AC control power shall be provided through an isolating transformer. All test voltage circuits shall be provided with optimum protection.

4.1.16 Anti-corrosion Protection

Sprayed Paint System

The switchboard materials to be spray-painted shall be derusted degreased, cleaned and receive an anti-corrosion treatment before the final coating system will be applied.

Powder Coating

The materials shall be derusted, degreased and cleaned before electrostatic powder spraying is applied. The coating shall be baked onto the material, offering proper protection against corrosion.

In principle, vendor’s standard color shall be applied, unless the requisition specifies another (RAL) color. Damaged painting shall be repaired with same type of paint and color before the equipment leaves the factory.

Sendzimir-Plated Steel

Sheet steel and structural parts which are used for the construction of the switchgear, certainly in areas where later access is impossible, shall be Sendzimir-Plated.

4.1.17 The entire switchboard and its materials shall be designed so as to limit fire propagation.

The switchboard shall not contain materials which will emit toxic fumes in case of a fire.

The application of PVC-insulated wire shall therefore not be considered.

Vendor shall confirm in his quotation that his material complies with this important requirement.

4.2 Compartments

4.2.1 Except for the openings for incoming and outgoing cables, the switchboard shall be completely metal-enclosed and compartmented.

4.2.2 The circuit breaker compartment, the contactor unit compartment, the main and the vertical bus compartment, secondary equipment compartment and the cable compartment shall be separated from each other by means of grounded metal partitions.

4.2.3 The front of the switchboard shall be provided with sheet steel doors matching a single outgoing circuit.

4.2.4 The compartments shall be made so that:

  1. Transfer of ionized gases between compartments will be prevented.

  2. Adjacent compartments will not be damaged when a unit is exposed to overpressures developing during an internal arching fault.

  3. Internal arching faults will be confined to the inside of the compartment where they take place. The protection devices in the power part will be limiting the duration of the fault.

4.2.5 The arrangement of the outgoing units shall take into account that air-cooler fan drivers (Company equipment identification TA) will be continuously in operation at full load and at the rated ambient temperature.

Attention shall be paid to the location of the starters with regard to the effect of the cooling capacity of the switchboard assembly.

4.2.6 The design of the switchboard shall be so that the required heat will be dissipated through the enclosure without the use of ventilation openings.

Should any ventilation openings be accepted in the purchase order as a deviation, then they shall be drip-proof and be protected against the penetration of foreign matter larger than 1.0 mm. Ventilation shall never be dependent on openings in the substation floor.

Moreover, ventilation openings will only permitted in compartments with a limited risk of overpressure caused by an explosion. This means that busbar compartments or compartments in which fuses or circuits breakers are mounted shall not have any ventilation openings.

If a ventilation space is needed at the rear of a switchboard with no rear access, this shall be clearly indicated in the layout drawings to prevent that the switchboard will be positioned directly against a wall.

4.2.7 All withdrawable units shall be accessible from the front.

4.2.8 A compartment shall be designed so that a separation from adjacent units and from the bus will be retained when a unit is withdrawn from the compartment. The stationary (bus side) disconnecting devices shall be completely guarded against accidental contact when working within the empty compartment space.

The following will be acceptable, in sequence of preference:

- Degree of protection IP 20. Irrespective of the voltage level and nature.

- Automatically operated shutters.

- Manually placed cover plates, which close the openings to the bus when the unit has been withdrawn.

The vendor’s leaflets shall clearly show the method of covering the busbar connection points.

For cover plates the following requirements apply:

- They shall be made of insulating material and be designed so as to prevent accidents during installation or removal. The compartments shall be lockable by key.

The busbar cover plates shall be colored red.

4.3 Busbar System

4.3.1 The three-phase power and neutral shall be carried by rigid busbars from the incoming feeder to the various units. All busbars shall be made of hard-drawn electrolytic copper.

The main busbars shall run over the whole length of the switchboard, with branch buses running down to the various units.

Busbar shall be silver-plated at spots where a contact is made using only the contact pressure of a spring.

4.3.2 The composition of the busbar system and the rating of all busbars shall be as indicated in the requisition and on the one-line diagram(s).

Each branch bus shall be capable of supplying the highest possible combined load of that section.

4.3.3 All buses shall be dynamically braced and thermally sized for the short-circuit currents and time as indicated in the requisition and on the one line diagram(s).

4.3.4 The switchboard shall be extendable at both sides, without drilling in the existing busbars.

4.3.5 The switchboard design shall prevent the occurrence and propagation of busbar faults. Preventive measures, for instance, will be:

  1. Insulation of the busbars

  2. Embedment of the busbars in cast resin

  3. Running bare copper bars, phases and neutral segregated, in an enclosure of an insulating material such as Pertinax or glass fiber reinforced resin.

Propagation of busbar faults shall be limited by separation of the busbar per vertical section. Special attention shall be paid to the separation of horizontal and vertical busbars and in bus risers.

4.3.6 The busbar system shall be completely insulated, unless specified otherwise in the requisition.

The insulation of the busbar system shall include all joints, tee-offs, and the bolts and nuts used for the connection. The connections to tee-offs shall be covered with suitable and reusable covers.

Protruding bolts and nuts in contact with current-carrying conductors of the busbar system shall be provided with insulating caps.

4.3.7 For the main power, path separation shall also be provided between both sides of a switching device.

This separation shall allow save working on the busbar on one side while the other side is energized. This separation shall be made of sheet steel, completely enclosing the live side.

4.3.8 The maximum permitted temperature rise of the busbars shall not exceed 30°K under full-load conditions and the room at maximum ambient temperature.

4.3.9 The design of the connection between the busbars and the draw-out unit shall be so that it will be impossible to make a short circuit when a draw-out unit is inserted. This means that a short circuit on the primary side of the fuses cannot occur.

4.3.10 The neutral bus rating shall be at least half the current capacity of a phase busbar. The neutral busbar shall be insulated identically to the phase busbars.

A removable neutral link shall be provided in the neutral bus over all circuit breakers and switches indicated on the one-line diagram(s).

4.3.11 The Earthing Busbar System

PE system

A single piece of bare copper ground bus shall extend throughout the length of the switchboard, with copper tee-off branches connecting all vertical units.

Each vertical section shall have its own vertical copper earth bar serving the earthing of the units and of all cables connected. The ground bus shall be mounted directly on the switchboard structure, thus earthing the structure. The minimum size of the earth bus shall be 25 x 5 mm.

The earthing bus shall not be used for neutral wire connections. At both ends provisions shall be made to connect 70 mm2 earthing cable.


The conductors of the PE and N shall be joined together at one spot in the switchboard. The Neutral bar can be current-carrying whilst the PE bar shall not be current-carrying.

Although some standards allow the use of the steel frame or structure of the switchboard as the main earthing conductor, this is not acceptable. In principle, an earth fault current shall flow through a cooper conductor, directly from the part where the fault occurred though its connection to the copper earth bar.

4.3.12 Switchboard Structure Earthing

The structure of a single vertical section can be considered as one part, provided adequate contact will be ensured between the different parts to the structure.

The earth contact of the steel frame of a draw-out unit shall preferably be made though a special earth contact device.

If the construction of the draw-out mechanism ensures a durable noncorroding multiple metal contact, which is proven and backed up by a test certificate, only then this construction will be accepted. The earthing contact shall be ensured before the main and the auxiliary contacts will be made.

4.3.13 All busbar joints shall be made of high tensile strength steel, bolts, nuts and washers.

All required prestressing torques for the connections in conductor paths shall be given in the maintenance manual. This document shall also clearly state at what intervals all connections shall be checked.

The vendor may apply a standard proven and tested method of joining busbar conductors, provided a test report on temperature rise and behavior over a longer period of time will be attached to the quotation.

Special designs for the connection to the vertical busbar will be acceptable provided test reports are available.

4.3.14 All connection bolts and nuts of busbar systems, including the connections at the busduct-hood, shall be accessible so that they can be checked with normal tools, also after installation and without dismantling of other compartments.

4.3.15 The busbar supports and the end-barriers shall be made of high quality nonhygroscopic nonflammable insulating material.

4.3.16 The earthing conductor of all incoming and outgoing cables shall have each an individual connection facility to the earthing busbar. This connection shall be done by means of a bolt and a nut.

4.3.17 The busbar shall be marked L1, L2, L3 and N, PE respectively etc., unless a color coding will be specified in the requisition.

4.3.18 When standing in front of an incoming or outgoing switching device, the phase sequence shall be the same from left to right. This sequence shall preferably be: L1, L2, L3, N.

4.3.19 The minimum straight distance in air, between all current-carrying busbar, shall be at least 20 mm, the distance between all busbars and any part of the steel structure shall be at least 25 mm.

The application of an insulating material to achieve these distances will not be acceptable.

4.3.20 All auxiliary busbars required for control or auxiliary power distribution, horizontally and vertically, shall be rated for the maximum current at the incoming terminal or at the tee-off point.

The minimum current rating shall in any case be no smaller than 60 A for the horizontal distributions and not below 16 A continuously for the vertical distributions. The reason is to avoid voltage drops in the internal wiring if heavy currents are drawn continuously or during operating peaks.

If wiring shall be applied for the vertical bus setup, then these wires shall not be interrupted, unless a construction with a compression-type lug or pin applied, joining the wiring in the lug.

The incoming terminals, switches and the connection of the auxiliary distribution shall be suitable for the maximum currents and for the connection of the required cables and matching wiring.

4.4 Wiring

4.4.1 The minimum cross-section of the control wiring shall be 1.5 mm2 and for current transformer secondary wiring this shall be for 5 A circuits: 4 mm2, and for 1 A circuits this shall be 2.5 mm2.

4.4.2 All internal wiring shall be insulated (1000 V grade) stranded cooper wire. For the insulation, a nonhalogenated type shall preferably be applied.

(Reference is made to DRAKA EDRATEEN). Vendor shall indicate an alternative if this requirement cannot be met.

4.4.3 All wire ends shall be terminated in lugs or wire pins of the compression-type.

4.4.4 Each wire shall be numbered at both ends with wire markers, and each wire shall be terminated in a separate terminal.

4.4.5 Wires shall not be joined between terminals or connection points.

4.4.6 Two wires under one terminal will not be permitted. Two wires permanently joined together in a compression-type lug or wire pin will be permitted.

4.4.7 The power circuit wiring shall be sized for the maximum possible fuse rating which can be used in the corresponding fuse holder.

4.4.8 Connection from the bus system to the fuse holder shall preferably be by insulated rigid bus. If cable or wire will be used, the minimum section will be 25 mm2, double-insulated from grounded metal parts and not touching equipment, other wires or any metal part.

4.4.9 All internal panel wiring, including the wiring between terminal blocks, shall be provided and installed by vendor.

Wire ways shall be provided for the wiring between units in the same cubicle, or between various cubicles without going outside the switchboard.

4.4.10 Wiring to doors or other movable parts shall be installed in adequately fixed flexible conduits.

4.5 Identification of Equipment

4.5.1 Durable and removable identification plates shall be screwed on the door or cover of each unit or compartment.

The switchboard shall have an identification plate with its ID, rated voltage, rated current and rated withstand currents, year of production, manufacturer’s references and type, as well as a reference to the standard according to which it has been built.

The nameplates to be attached to the incoming and outgoing circuits can be found in the schedules, forming part of the order documents.

The following indications shall be given on a unit ID plate:

- Equipment number

- Function

- Rated kW.

If any other engraving is required, this shall be indicated in the requisition.

The text of other ID plates shall be given be purchaser later, on a separate nameplate list to be provided by vendor.

4.5.2 All relays, fuses, auxiliary switches, terminals etc. shall be labelled in a accordance with the approved wiring diagram. Equipment markers shall be permanently attached to the fixed part of the equipment.

The nameplates, ID plates and labels shall be durable, not sensitive to wiping or dirt. (White Resopal or identical material with black engraving).

4.5.3 The minimum standard letter height is 6 mm; for larger size plates the engraving shall be larger sized accordingly.

4.6 External Cable Connections

4.6.1 All cables shall enter the switchboard from below through openings in the concrete station floor, unless otherwise specified in the requisition.

4.6.2 A separate vertical cable compartment shall be provided in each vertical section to contain all incoming cables for that section. Clamping facilities shall be provided to support the cables at different heights in the vertical section. Where the cables enter the vertical section at the bottom, the first clamping facility shall be provided.

Sufficient space shall be provided to bend and mount the cable cores free from contact with any metal part of the switchboard.

4.6.3 Provisions shall be made for the connection of each incoming and outgoing and its ground wire with a separate screwed or bolted terminal supplied with the switchboard. The terminals shall be installed so that they are easily accessible, even when standing outside the switchboard and the maximum number of cables will be installed in the cable compartment. All terminals and the connection screws shall be sized properly for cable lug, the conductor core and the ground wire cross-sections included.

4.6.4 It shall not be allowed to run bare copper conductors in the cable compartment, with the exception of the PE conductor. These compartment shall only house the terminals for the outside cabling.

4.6.5 Cable glands for PVC or XLPE insulated cables will not be required for switchboards located indoors with the cables entering the switchboard from below. If, however, these cables enter the switchboard from the top, vendor shall provide removable gland plates.

4.6.6 Lead covered cables with a flexible earthing conductor underneath the lead cover shall be provided with a special spring-type cable clamp (3M). The earthing conductors of the armor and the lead cover earth wire will be compressed in the same cable lug. The special cable clamp shall be provided by purchaser.

4.6.7 If a lead covered cable design without an earth wire under the lead cover will be used, then brass cable glands shall be used to earth the lead cover. The brass glands shall be provided by purchaser. The clamps in which the glands are mounted shall be provided by the switchgear manufacturer. (Attention shall be paid to the quantity of control cables.)

4.6.8 Connections for single-core cables shall be provided with a cable termination set, consisting of a copper bar system with relevant multibolt type clamps suitable for the cross-section and the number of cores specified.

4.6.9 Compartments containing incoming cables or busducts shall not be used for the connection of secondary cables or auxiliary power cables.

4.6.10 Only if specified in the requisition, a cable gland plate in the bottom of the switchboard shall be specified.

The metal gland plate shall be of the split-type not being provided with holes for the glands to be provided by purchaser.

4.7 “Spare” and “Space” Compartments

4.7.1 A space is the part of the fixed installation ready to accommodate a draw-out unit. This means that the fixed part shall be completely punched, drilled, tapped and/or otherwise prepared to accommodate any of the various types of units, applying a minimum of field labor.

4.7.2 The necessary take-off points for the power and the control supply shall be provided in the space compartment.

4.7.3 A “space” shall be covered with a blind door.

If the space shall be completed with a draw-out unit, then the matching door shall be supplied with the draw-out unit.

4.7.4 Spaces shall be indicated with “Space” on the one-line diagram and on the front-view drawings. The blind door shall have a label: Space maximum kW. The kW rating to be indicated will be the maximum kW rating of the draw-out unit to be installed, equipped identically to the other units of the same size.

4.7.5 A spare unit is a completely functional unit, ready for operation after cable connection and a possible exchange of the power fuses and/or the thermal relay.

The units indicated as “spare” shall be complete, including the supply of draw-out unit for the type and size of circuit specified. The unit shall be designed for the maximum rating to be connected.

5. Components

5.1 Ratings

5.1.1 With regard to the insulation level, current ratings and short-circuit capacity, all equipment and components shall be suitable for application with a supply system specified in the requisition and one-line diagram(s) at the given ambient temperature of the room in which the equipment will be located.

Special requirements such as resistance to shocks and very high humidity or an aggressive atmosphere will be specified separately.

5.2 Circuit Breakers (Power Circuit)

5.2.1 The circuit-breakers shall be of the air-break type.

5.2.2 The circuit-breakers shall be anti-pump and free to trip instantaneously if closed on a short circuit, whether manually or electrically, even when the operating handle or switch will be held in the “close” position. The protective tripping device can either be integrated in the circuit breaker or be a separate unit mounted in the switchboard.

The anti-pump feature shall be maintained despite the loss of the bus voltage during a fault.

5.2.3 The circuit-breakers shall release the motional energy in one continuous action, so that the speed and the force of operation will be independent of the action of the operator or the mechanism.

5.2.4 The metal frame of the circuit breakers shall be earth by means of copper brushes or self-centering earth contact pins. The contact to earth shall be made well before the main power contacts are made and the circuit breaker can be closed.

Circuit-breakers having a double insulation without a metal frame need not be grounded.

If the circuit breaker frame will be earthed through the wheels of the moving mechanism, this shall only be acceptable provided a test certificate from a recognized short-circuit laboratory proves that this construction is adequate and will still be completely functional after the rated short-circuit switch-off current has flown through a wheel. This test shall be backed up by a test certificate. If this cannot be produced, then the circuit breaker shall be earth according to one of the methods described above.

5.2.5 It shall not be possible to move a closed circuit breaker from its position.

This is applicable to both the engaged and the test position. Moving the circuit breaker may only be possible if the main circuit breaker contacts are open.

It shall not be possible to close a circuit breaker, either mechanically or electrically, in any possible between the test position and the plug-in position.

5.2.6 The circuit breaker shall be moved mechanically with the compartment door closed, thus limiting the escape of gases in case of an internal fault during the movement of the circuit breaker. Opening the door to the circuit breaker compartment shall only be possible when the circuit breaker is in the disengaged position.

5.2.7 When the circuit breakers are lifted out of their test position, for instance for inspection or maintenance, their stored energy shall be discharged before lifting-off is possible.

5.2.8 All circuit breakers of the same current rating size shall be fully interchangeable.

To prevent interchangeable problems, special controls shall not be mounted directly on the circuit breaker, but in the relative LV control compartment.

5.2.9 The weight and the capability of two men handling the circuit breaker in and out of its cradle shall determine the need for the use of a circuit lifting truck. The maximum weight to be handled by two men shall not exceed 70 kg. When this weight is exceeded, a circuit breaker lifting truck is required to lift the circuit breakers out of the compartments and to transport them to and from any other location and to position them as required.

Vendor shall quote such truck(s) separately under the heading:


The supply of these trucks shall be part of the switchboard order. One truck shall be provided for each station in which the LV switchboards with heavy circuit breakers are installed.

5.2.10 The closing and winding control power for electrically operated circuit breakers will normally be derived from the busbar system.

A step-down transformer will be required if line to line voltages of over 380 V will be applied. In this case each circuit breaker shall have its own control power transformer.

The tripping power shall be proved from a DC supply specified in the one-line diagram.

Manual charging of the stored energy mechanism will be required when closing power is not available.

Manual closing and tripping of all circuit breakers shall be possible when standing in front of the switchboard. Both pushbuttons shall be protected by a flap or cover against accidental operation.

5.2.11 The circuit breakers shall have a mechanical indication of the open and closed position and load condition of the stored energy mechanism. These indications shall be visible when standing in front of the panel.

5.2.12 In addition to the required auxiliary shaft-driven contacts required for the given control setup, all circuit breakers shall be provided with two single-pole change-over auxiliary contacts; they shall remain available as spares for future interlocking purposes.

These spare contacts shall be completely wired to terminals.

5.2.13 The arcing chamber of a circuit breaker pole shall not contain any asbestos.

5.2.14 Adequate space shall be provided around the arcing chambers to allow for cooling-down ionized gases formed during the switch-off of the rated through-going short-circuit current.

5.2.15 Circuit-breakers shall be provided with facilities to lock them in the withdrawn position. In additional interlocking with the upstream or the down stream circuit breakers will be required, this shall be shown on the one-line diagram. If not all types of interlocks can be applied, vendor shall state this in his list of deviations.

5.2.16 Circuit-Breaker Integrated Protection Relays

Circuit-breakers shall only be provided with an integrated protection relay if specified in the requisition.

If an integrated protection relay will be specified, this shall be equipped with a testing facility to check the protection relay whilst the circuit breaker remains in operation. Only if this last requirement is met, then an integrated protection relay is acceptable. If the testing facility cannot be offered, then a panel mounted protection system shall be quoted.

5.3 Fuses (Power and Measuring)

All fuses shall be suitable for the voltage levels applied. If two voltage levels shall be applied, then all fuses shall be suitable for the highest level.

5.3.1 The fuses shall be of the high-rupturing capacity type and be rated to protect the switchboard equipment, including the thermal relays and the connected power cable against short circuits.

The knife-type fuses to be applied shall be of the gL type according to VDE 0636, Teil 1. If gR type fuses shall be applied to starter units of special electronic devices, this shall be indicated in the switchboard schedule.

The fuse coding gL will sometimes also be given as gI.

The application of aM type fuses will not be permitted, unless the requisition specifically specifies that aM types shall be applied.

In other fuse constructions or characteristics shall be applied, for instance according to BS or NF, this shall be specified in the requisition.

The fuse characteristic, however, shall comply with IEC.

The fuse size specified in the schedules shall be strictly adhered to as the characteristics of this fuse have already been used to size the related power cable, taking into account the DOL run-up time of the motor.

All fuse holders shall be protected against accidental contact and, therefore, shall have a degree of protection of IP 20 with the fuse installed in the holder. The degree of protection shall be independent of the position of a cover or the draw-out unit. Fuse separation plates shall be installed between all fixed mounted fuse holders.

The fuse-pulling grips on the fuse body shall be made of insulation material or be of a metal designed not to be in contact with the knife blade.

5.3.2 The fuses for motor circuits shall furthermore be sized, and have characteristics so as to allow for DOL motor starting.

5.3.3 Screw-Type Fuses

Screw-type fuses shall only be applied when specified in the requisition. In this case they shall meet the following requirements:

Screw-type fuses may only be installed in systems with a limited short-circuit capacity, being backed-up by high rupturing capacity fuses. The use of screw-type fuses shall be restricted to values not exceeding 25 A.

All screw-type fuses shall be of the E27 type.

5.3.4 All fuses shall have a “trip” indicator.

5.3.5 If fuses are used, for instance, in measuring circuits and need be replaced while the busbar system is energized, precautions shall be taken to prevent a contact with any live parts.

5.3.6 Measuring fuses shall be installed as close as possible to the busbars. The connection between the busbar and the primary side of the fuse shall be completed with an insulated wire running in an additional insulation sleeve. Where the sleeve is crossing partitions or the like, suitable grommets shall protect the sleeve against mechanical damage. Primary MCB’s shall not be used for measuring connections to the busbars.

5.4 Internal and External Control Circuit Protection

In principle, MCB’s shall be used; fuses may only be applied if specified.

Please note that the requirements specified below for MCB’s will also be applicable to fuses if specified in the requisition.

5.4.1 Miniature Circuit Breakers (MCB)

A short circuit in the internal and the external control wiring shall ensure instantaneous tripping of the MCB.

24 VAC or DC shall not be applied for control.

For control voltages of 48 VAC or DC and above, a maximum loop resistance of 9.5  shall be taken into account.

Vendor shall also take into account the internal resistance of the pole(s) of the applied MCB’s.

For MCB’s installed in metering circuits behind VT’s, special attention shall be paid to the fact that the short-circuit capacity of the transformer shall be sufficient to trip the MCB instantaneously on a short circuit somewhere in the protected circuit.

5.4.2 Discrimination of MCB’s

As the short-circuit capacity of control power supply systems in general is very limited, the application of series-arranged MCB’s will not be permitted, neither in control nor in measuring circuits. This means that a control bus of a switchboard will be protected by its external feeder and that only one MCB will be connected between this bus and the control system of each circuit.

The current rating of a MCB shall be selected as low as possible to ensure instantaneous tripping of the device with the actual short-circuit level. Together with his drawings and documents, vendor shall provide a calculation of the rated current of each circuit.

During the inspection, vendor shall prove proper protection and tripping of all MCB’s.

5.4.3 Switch-off Capability of MCB’s

For MCB’s connected to a control circuit using Ln - N, the control MCB shall be connected in series with the power fuse of the Ln phase ensuring adequate back-up protection as required by the manufacturer of the MCB.

Reference is made to ABB, Z series, MCB’s (latest version).

5.4.4 Auxiliary Contacts of MCB’s

When indicated in the documents, the MCB’s applied shall have a contact which will be activated when the MCB will be tripped by an overcurrent. This “trip” contact shall be used for external alarm purposes. The “trip” contact shall not be activated when the MCB will be switched off manually.

Each MCB shall have the number of auxiliary contacts switched together with the main contacts as specified.

5.4.5 It shall be possible to padlock MCB’s installed in fixed mounted circuits in the “off” position.

5.4.6 All poles of multipole MCB’s shall be switched simultaneously.

5.5 Contactors and Mechanical Relays

5.5.1 The contactors shall be of the three-pole air break type. The contactor shall be held in the closed position either magnetically or mechanically as specified in the requisition or its related documents.

5.5.2 The rated operational current of the contactor defined in IEC 158-I, shall be for motor-circuits at least 125% of the rated full-load current of the motor. The minimum contactor current to be applied will be 20 A, rated Ie at the system voltage under AC3 operating conditions.

The contactor in a draw-out shall be capable of switching the maximum power connected to the draw-out unit, taking into account the above requirements.

In order to maintain complete interchangeability, all nonmotor-type contactor-switched units shall have the same size of contactor for the identical size of draw-out units.

5.5.3 The number of switching operations per hour shall be as specified in the requisition.

5.5.4 The contactors shall be capable of withstanding for at least five seconds, if a longer run-up will be specified for at least the duration of the run-up. After the run-up time, they shall be able to break the locked rotor current of motors so that the locked rotor current is 800% for “EEx e” type motors and 700% for all other types of motors.

The locked rotor power factor can vary between 0.75 and 0.25 depending on the size of the motor.

Where a core balance earth fault protection relay will be provided, the contactor shall be capable of switching off the earth fault current flowing in the connected cable between a phase and earth without welding the contacts.

5.5.5 For switching of currents exceeding the breaking currents of the starter, reference is made to IEC 947, part 4, type 2 (formerly: IEC 292 coordination, type C). Welding of contacts will not be acceptable. In order to remind the maintenance engineer to inspect the contactor contacts after an earth fault trip, a warning shall be attached near the reset button of the earth fault tripping device:

“Inspect Contactor Contacts Before Energizing!”

5.5.6 When selecting contactors and fuses for switching capacitors or capacitor banks, attention shall be given to the inrush current and break of capacitive currents.

5.5.7 All contactors shall be provided with sufficient auxiliary contacts. These contacts shall be wired to terminals as shown on the wiring diagram of this specification. Spare contacts shall only be provided if specifically indicated.

The contact rating of auxiliary contacts shall be 6 A minimum, 250 VAC. In case of DC currents, the contact rating shall at least be suitable for the whole life time and number of operations of the contactor.

5.5.8 The AC control voltage for outgoing circuits, if directly supplied from the unit’s main power circuit, shall be connected between the L1 - N.

The control system shall be as specified in the requisition.

5.5.9 Magnetically held contactors shall operate with a control cable of 300 meters in length, the conductors being 2.5 mm2 of which 5 cores will be energized when the circuit shall be interrupted to trip the contactor, while the control voltage shall be at its maximum rated value.

When the contact in the control switch opens, the total capacitive current flowing through the “hold” line shall not be capable of holding the contactor in the closed position; the contactor shall trip without any delay.

The applicable type of control cable and the control method applied will be specified in the requisition.

An auxiliary relay shall be installed if the contactor has a high inrush current.

5.5.10 A contactor in a circuit, applying a time-delayed undervoltage trip, shall operate instantaneously when switched off by the external controls. The external controls shall be of the pulsing type: 200 ms.

5.5.11 The contactor, relay or circuit breaker coils for closing and/or tripping or control, shall be suitable to operate between 80 and 110% of the rated control voltage.

Magnetically held systems or coils suitable for continuous operation shall be suitable for continuous energization at the above voltage levels.

Closing coils requiring a minimum time of energization before the movement of the mechanism is completed shall have a built-in time-delay device ensuring that the action is completed independently of the activating contacts closing time.

Tripping coils or any other coils not suitable for continuous energization shall be automatically switched out of the circuit once the required action is completed.

5.5.12 The operating mechanism of the unlatching device shall be designed so as to operate when required, even after a prolonged nonoperational period.

5.5.13 Relay or auxiliary contactor contacts shall be self-cleaning and have a contact material suitable for a guaranteed functional use in the describe atmosphere.

Contact corrosion through, for instance, sulfur fumes in the air shall not be prevented.

Contacts shall also be suitable for low current circuits as applied in electronic circuits.

5.6 Switches

5.6.1 Switches in incoming power circuits shall have the following number of poles:

- 3-phase 3-wire circuits: three poles.

- 3-phase 4-wire circuits: four poles.

Switches in incoming auxiliary power circuits shall have the following number of poles:

- 3-phase 3-wire circuits: three poles.

- 3-phase 4-wire circuits: four poles.

- AC circuits: two poles.

- DC circuits: two poles.

5.6.2 Switches in outgoing power circuits shall have the following number of poles:

- 3-phase 3-wire circuits: three poles.

- 3-phase 4-wire circuits: four poles.

- for AC circuits: two poles minimum.

5.6.3 Contactor controlled outgoing units shall be provided with a switch in the main power, capable of switching off the inrush current of the maximum size motor connected to the unit (IEC 408 AC-23).

The rated current of the switch shall be equal to or larger than the Ie of the contactor.

For large motors the actual impedance of the cable between the switchboard and the motor can be used to determine the maximum actually inrush current.

5.6.4 Switches used for other applications shall comply with IEC 408 AC-22.

5.6.5 The switching capacity of the device shall be indicated for AC-22 and AC-23 duty. In order to enable the service engineer to identify the applicable AC category, a label shall be attached showing the category.

5.6.6 Switches for AC outgoing circuits shall have an Ie rating of minimum 25 A AC 22. The Ie rating might be specified differently.

5.6.7 Switches for DC circuits shall have a minimum Ie of 63 A DC 21.

5.6.8 Switches shall be suitable for installing auxiliary contacts as an add-on pack when required by the control circuit. The contact rating shall be at the same as specified for the auxiliary contacts of contactors.

5.7 Draw-out Units

Basically a draw-out construction shall be provided. If the weight and/or the contact capability of the busbar contacts will be exceeded by the maximum current required for the starter, only then a fixed mounted construction will be acceptable. The weight to be handled by two men shall not exceed 70 kg.

5.7.1 A draw-out unit shall occupy one vertical space over its full horizontal width in the starter compartment.

The vertical space for the cable connection to the unit in the cable compartment shall be dedicated to this one draw-out unit only.

The above excludes the application of more than one starter adjacent to another starter in the same vertical section.

5.7.2 All units shall be completely withdrawable; the power and control wiring shall be automatically connected and disconnected.

A semi-withdrawable system will not be acceptable.

5.7.3 A draw-out unit is an assembly - in any combination - of a switch, fuses, contactor, protection relays and/or other relays that can be withdrawn as a completely functional unit from the fixed part of the switchboard structure. It shall, once in the engaged position, be an integral part of the switchboard structure.

During the movement of the unit, it shall be supported by the switchboard structure. A stop shall protect the unit in the completely draw-out position from overshooting.

The moving mechanism shall have adequate means to make sure that the contacts are fully made.

5.7.4 Two positions of the unit will be required:

  1. The full “in” position: both main and control circuits are connected.

  2. The full “out” position: both main and control circuits are disconnected and provide a safe distance between live parts and the unit.

5.7.5 The draw-out units shall have a mechanical interlock with the door so that opening of the door will be impossible when the main power path switch is closed.

The interlock mechanism shall be self-aligning with the part fixed on the door.

The mechanism shall prevent closing of the main power switch when the door is open, and the unit is not in the fully racked-in position. The unit shall be locked in position when the main power switch is switched on.

Manual closing of the main power switch, without employing tools, will be prohibited.

An auxiliary contact on the main power path switch shall prevent closing of a magnetically held contactor in any other position than the completely engaged position.

Opening of the main power path switch shall trip the contactor through this same contact. Tripping shall be accomplished by the contact and not by the loss of control power.

Closing of latched contactors shall be prevented and tripping be initiated by the main power path switch auxiliary contacts, identical to the above.

5.7.6 All draw-out units of the same size and identical controls shall be completely interchangeable. Adjustment to the kW size as far as the fuses and thermal relays might be required.

However, if special control is required this shall be done outside the draw-out unit in order not to interfere with the interchangeability principle.

5.7.7 A padlock facility acting on the operating lever of the main switch outside the door shall be provided to lock the switch for maintenance. Adequate means shall be provided to install more than one padlock on the switch.

5.7.8 Heavy draw-out units shall always be located in the lowest part of the switchboard. When different sizes of draw-out units will be installed in a vertical section, then the weight of the draw-out units shall decrease with their installed height.

5.8 Protective Relays

5.8.1 The protective relays shall be of the specified make and type. If no make or type will be specified, they shall have the characteristics specified in the requisition or on the one-line diagrams.

5.8.2 The protective relays shall be provided with operating indicators which shall be manually reset without having to open the doors.

5.8.3 The auxiliary power supply for electronic protection relays shall be a battery backed-up DC source from outside the switchboard. The DC supply system will be provided with a three-phase regulated rectifier bridge charging the battery with a DC having a ripple.

5.8.4 For the testing of the protection relays, a test socket and test plug shall be provided if indicated in the documents. The arrangement of the test socket shall be so that the trip wiring during testing will be interrupted, the current transformers will be short-circuited and the potential transformers will be switched double pole out of the circuit.

5.8.5 The thermal relays used for motor protection shall be of the three-phase type, offering protection against single-phasing. The relays shall have a manual reset facility which shall be operable from the front only. The unit door shall remain closed during the resetting operation.

The thermal relays shall have ambient temperature compensation.

5.8.6 The application of current transformers for protection relays of larger motors will be permitted, but only if economically justifiable.

If the typical outgoing circuit diagrams require differently, then current transformers with a secondary current of 1 A shall be provided.

5.8.7 The starting conditions are: two run-ups from cold condition, one start-up from hot condition.

5.8.8 The protection relays for “EEx-e” motors, to be installed in outgoing circuits, shall have the correct time-current characteristics, tripping the motor within its specified “te” time. A certified time-current curve of the related relay shall be fixed on the inside of the door of the units powering “EEx-e” type motors.

5.8.9 If a long run-up time will be specified, the outgoing unit shall be provided with special facilities to ensure the run-up (e.g. using saturation CT’s).

5.9 Metering and Protection Transformers

All metering and protection transformers shall comply with the relevant IEC recommendations.

5.9.1 Current circuits for measurement and protection purposes shall always be galvanically separated, unless specifically indicated otherwise on the drawings.

The transformers shall maintain sufficient accuracy under all overload and short-circuit conditions, ensuring proper protection relay operation, maintaining the required discrimination.

The rated output of the current transformer shall be selected to match the actual burden, taking into account all possible impedances including external cabling.

The current transformers shall be of the single-phase type. The secondary current shall be 1 A.

The current transformers shall be selected according to the following table:

Measuring Cores (according to IEC and VDE)

Class 0.5 Tariff, only if specified.

Class 1 Metering.

Class 3 Overcurrent relays.

For measuring cores the rated overcurrent factor shall be as small as possible, for instance M5 or M10, to protect the connected instruments from excessive overcurrents.

Protection Cores (according to IEC and VDE)

5P (10P will only be acceptable in special cases).

Attention shall be paid to the overcurrents occurring during inrushes and the matching settings of the relays.

In principle the I >> for outgoing circuits will always be set over the inrush current of the device, to prevent nuisance tripping. For a transformer the inrush current shall be taken as 1/uk x In, any reduction factors shall be neglected.

The transformers shall be capable of withstanding the rated and momentary peak current specified for the switchboard.

Current transformers secondary circuits shall not pass though automatic disengaging control connections, unless it will be ensured that the main power path will be interrupted before the secondary will be opened, and vice versa.

5.9.2 Core balance transformers encircling all normal current carrying conductors of the internal switchboard wiring of a circuit shall preferably be used for earth fault protection instead of the residual current arrangement.

5.9.3 Voltage transformers shall comply with IEC 186, Table 1, for the rated voltage factors. The transformers shall not exceed the maximum temperature and accuracy limits.

5.9.4 Voltage transformers shall be protected by means of fuses at the primary side and by MCB’s at the secondary side.

5.9.5 CT’s and VT’s in the switchboard shall be located so that they are accessible for terminal maintenance without dismantling of any wiring.

Replacement of CT’s shall be possible with only minor efforts; this means that, if a mounting plate on which control circuits are installed must be removed, only a minimum of wiring must be disconnected. This can be accomplished, for instance, by properly locating the terminals.

5.10 Transducers

Reference is made to IEC 688 (part 1) and IEC 255.

5.10.1 Transducers for the transmission of actual values to external indicating instruments shall be installed inside the draw-out unit.

5.10.2 The primary current input of a current transducer shall be 1A.

The primary voltage input of a voltage transducer shall be matched to the selected measuring voltage given in the documents.

5.10.3 The input and the output of a transducer shall be galvanically separated.

5.10.4 If not stated otherwise in the requisition, the output shall be 4 ÷ 20 mA (into a burden of 100 ).

5.10.5 For measured values other than the AC current, 4 ÷ 20 mA or 1 ÷ 10 VDC shall be selected depending on the transducer selected.

5.10.6 If the output value will not be indicated in the bid documents, vendor shall state in his quotation the proposed output rating.

5.10.7 If an input voltage for the measured value will be required, it shall be derived from that part in the power circuit required for proper operation of the transducer.

5.10.8 All auxiliary power required for a transducer shall be derived from a source inside the draw-out unit.

5.11 Measuring Instruments

5.11.1 The instruments shall be flush-mounted in the front of the switchboard; minimum size shall be 96 x 96 mm.

Smaller size instruments will be acceptable on draw-out units only.

5.11.2 Remote instruments shall not be wired in current circuits of protection system.

5.11.3 Instruments connected to measuring transformers shall have characteristics which correspond with the characteristics of the measuring transformers.

5.11.4 Voltmeters shall have a maximum scale reading of 150% rated voltage.

Ammeters for motor circuits shall be provided with a compressed end scale or 800% of the rated full-load current.

The end scale of ammeters for incoming and outgoing feeder circuits shall be 200%.

5.12 Signal Lights

High intensity LED’s shall be used for the required indications. The LED’s and the matching current limiting device shall be sized to withstand the overvoltages on AC and DC circuits.

The LED’s shall be of a design identical to incandescent lamps, being housed in identical rigid metal fittings. The LED’s shall have a bayonet type lamp base.

Specially designed LED’s for indication functions will be acceptable only if approved before order award.

The application of steep-down transformers will not be acceptable.

Resistors in series with LED’s shall be sized so that at least 25% spare power can be dissipated by the resistor.

Capacitors shall be sized to continuously withstand the maximum connected system voltage x 1.15.

5.13 Control Terminals

All control terminals shall be of the rail-mounted design and be of the spring preloaded type (make Klippon: type RSF3 or an identical one from Entrelec).

5.13.1 Specially designed connections, such as applied for the automatic disconnection of the draw-out unit, shall have adequate means for connection, fixing and screening of the different live parts. The fixed part of this connection shall be self-centering with the movable part.

The fixed part shall be easily accessible or removable so that the control cabling can readily be installed in a cable compartment.

5.13.2 All terminals carrying the same voltage shall be grouped together. This means that, in principle, the terminals of a circuit protected and switched by the same device form one physical unit. Another protecting and switching device creates another “different” voltage.

Different voltages shall not be combined in one block or physical blocks of terminals. In order to recognize “different” voltages, either a minimum distance of 5 cm shall be maintained between the blocks or groups with “different” voltages or a barrier of insulating material shall be fixed between such terminal blocks of groups.

The barriers shall extend at least 1 cm beyond the terminals.

5.13.3 The first terminals in an LV control compartment, to which the secondary wiring of a current transformer will be connected, shall be provided with a short-circuit device. This device, when open shall not be closed by gravity or vibration forces, thus preventing unintentional short-circuiting of the current transformer circuit.

5.13.4 All terminals and connections located in or adjacent to the cable compartment, which are normally accessible for the connection of outside cabling, shall have a mechanical protection to prevent accidental contact of live parts with the conductors of a cable or with tools.

The protection shall keep the foreign parts away from live parts and not guide them towards the live parts as in the case with flexible tubing.

If a cable shall be installed, access to the live part which was connected shall be impossible.

5.13.5 The control or auxiliary power terminals shall only be located in LV control circuit compartments.

The control and auxiliary cabling to these terminals may run through power compartments provided the cabling can be installed without opening the power compartment.

This can be done by using a completely enclosed cable duct or conduits through the power compartment.

5.13.6 All terminals shall be mounted so as to ensure easy access after installation of the wiring and the cabling. Therefore, a multilayer terminal arrangement will not be acceptable.

5.14 Electronic Auxiliary Relays

5.14.1 Electronic auxiliary relays used, for instance as timers, in general, are operated by means of voltage signals, the internal resistance being very high.

In practice, this means that - contrary to normal magnetically operated relays - problems can arise when the activating range of the relay is operating outside the normal range of

80 ÷ 110% Un.

5.14.2 The application of electronic relays will only be permitted in circuits where the initiating contact for the time delay is inside the control circuit in the draw-out unit and external wiring is not connected in parallel with this initiating contact.

5.14.3 If external wiring will be involved, magnetically operated relays shall be applied direct acting as contact multiplier.

Note: These requirements were made because this type of electronic relays energizes when 50% Un is present on the activating terminal.

For safeguarding reasons (to prevent energization of a relay ) the A side of the coil will often be connected to the B side. If this is done with the activating terminal of an electronic relay a very dangerous situation may arise:

- In case of a short circuit inside the control switch near the motor, between the control power supply side and the B side of the relay the following will take place:

  • Because of the very high impedance of the input of the electronic relay, the conductors of the cable to the control switch will be voltage dividers, resulting in the presence of  50% control power at the incoming terminal of the electronic relay!

  • Quite contrary to conventional relay applications, the electronic relay will energize. As it is obvious that this must not occur, a mechanical relay shall act as interposition!

5.15 Earth Fault Leakage Protection

5.15.1 AC

If outgoing circuits shall be provided with EF protection as indicated in the documents, the EF protection shall consist of a system a core balance CT and a separate detection relay.

The EF protection shall act on a differential current of no less than 500 mA.

The vendor shall take into account the actual voltage of the power distribution system when selecting the EF protection device with regard to the system voltage, for instance when applying EF protection on 660 V 3-phase systems. Attention shall be paid to the voltage required for a device built-in testing circuit, in particular for system with DC control.

The EF protection shall be of the manual reset design. Resetting shall take place inside a starter unit.

5.15.2 DC

If DC will be used as outgoing control, the DC power supply to the units in a vertical section shall be provided with an earth fault leakage monitor, make HOLEC, type ELM. This device will detect a through-going earth leakage and give an alarm. The delta current shall not be lower than 20 mA. The ELM’s shall be wired in parallel per switchboard for a common failure indication. The ELM relay shall be visible from the front of the gear to detect the faulty section.

5.16 Control by an External Digital Control System

The external control systems intended are a DCS, a PLC or a PC.

5.16.1 The interface between the installed starter and the communication bus inside the switchboard shall be in each indicated starter. The draw-out requirement of a unit will remain in force. The connection to the communication bus and the interface shall be made using self-centering plugs and sockets.

5.16.2 The electronics of the interface shall be suitable for mounting inside a starter unit. The cooling capacity of the cable compartment may be used, provided the integrity of the separation shall not be harmed by the ventilation requirements of the electronics.

5.16.3 The interface shall act as intermediate between the digital system and the starter only. The commands from the local control switch near the motor shall be completely independent of the interface, even if the interface is defective.

5.16.4 Each interface shall perform a self-checking procedure and report an internal failure to the common processor.

A failure in the unit shall result in a trip of the starter. The failure shall be visible on the front of the switchboard.

5.16.5 If starter status lights will be incorporated on the interface, they shall be of a different color.

5.16.6 Any indications on the interface itself shall be given preferably on a digital display.

5.16.7 The interfaces shall be connected through the communication bus to the central processor unit of the switchboard. This central processor will be the link with individual interfaces and the outside control system.

5.16.8 The total control system in the switchboard shall be capable of riding through power failures. It shall not change any status as the result of a power failure.

The ride-through capability shall be at least 5 minutes. The auxiliary power to the system shall be at the AC distributed in the switchboard.

5.16.9 The software required to operate the system in combination with one of the above described systems belongs to the scope of supply.

5.16.10 The make and type of the external digital control system shall be indicated in the documents. The required communication protocol shall be arranged by vendor. Vendor shall confirm before order award that his system is perfectly operational and communicating together with the given external control system.

6. Tools

6.1 Vendor shall supply with his switchboard a tool kit with all tools necessary to maintain the switchboard.

The supply of tools shall be limited to parts normally not available in an electrician’s tool box.

Vendor shall describe in his quotation in detail the tools in the tool supplied with the equipment.

The supply of the switchboard tool box is an integral part of the order.

7. Spare Parts

7.1 Vendor shall recommend initial spare parts and spare parts for two years of operation.

7.2 Initial spare parts to be supplied with the switchboard:

- Two sets of three fuses of each type and size supplied in the switchboard.

- One MCB of each size and type supplied in the switchboard.

- Two LEDs of each type and size used in the switchboard.

- One thermal relay of each type supplied in the switchboard.

The lot described above is an integral part of the order and shall not be offered separately.

7.3 Vendor shall offer separately the spare parts for two years of operation.

8. Inspection and Tests

Inspections and tests shall be carried out in the factory and on site, as stated in the requisition.

All test equipment necessary for performing these tests shall be furnished by vendor.

All costs of inspections and testing in the factory and on site and the test equipment at both locations will be included in the purchase order.

8.1 Quality Control by Vendor

Before the witnessed Inspection and Testing by the Client and or Company, the switchboard(s) and each individual circuit shall be checked by vendor on their operability and functionability.

Vendor shall perform function checks of all draw out-units. This shall include a trip action of the thermal relay. The relay tripping time shall be checked against the applicable curve.

Faulty thermal relays shall be replaced during this check.

Vendor shall check all protection, interlocking, control systems and automatic transfers, set all times and measured value inputs as specified. The check of the tripping capability of the MCB’s belongs to vendor’s scope of supply.

Vendor shall check compliance of the materials with the applicable specifications and standards.

Vendor shall keep a record of each test which has been performed. The record shall be verified by the Inspector.

Please note the following:

Despite the above vendor testing of the equipment, the Inspector shall witness random tests of 10% of the draw-out units and all control, interlock and transfer systems, including activation of all protection and sensing relays in these systems.

If a failure occurs or incorrect testing by vendor will be established, the Inspector shall prove the functionability of the units or the systems.

After the above unwitnessed quality control by vendor, purchaser shall be notified of the date of the witnessed inspection and testing.

Notification shall comply with the purchase documents.

8.2 Witnessed Inspection and Testing

All tests shall be witnessed by a representative of the Client and/or Company.

8.2.1 The tests and inspections shall be carried out in the factory.

The Standard Inspection procedure for LV switchboards as an integral part of this specification, covers the tests and inspections to be carried out in the factory.

8.3Tests, Inspections and Proof Operations to be Carried out on Site

8.3.1 Megger test, resistance between the buses mutually and buses to ground must be at least 10 Megohm.

8.3.2 High potential test for one minute:

- 2500 Volt for maximum 660 VAC switchboard

- 3500 Volt for maximum 1000 VAC switchboard.

8.3.3 Inspection of all bolted connections on the buses and, if a busduct between the switchboard and the power transformer or a busduct between switchboard will be in vendor’s scope of supply, also the bolted connections in the busduct and its connections to switchboard and power transformers.

8.3.4 Inspection of all terminals to verify that during transport and handling no terminals including markers are missing or damaged and the wiring in the terminals is still secured.

8.3.5 A visual inspection ensuring that switchboard is free from dust, waste and/or tools.

8.3.6 Proof operation of the distribution system, the change-over system etc. including testing of all protection relays of the distribution system and the electric motors.

9. Client’s Additional Requirements to Company’s Specification/Requisition

(To be completed during project execution)

10. Deviations from Specification and Requisition

(To be completed during project execution)


11. Approved Vendor Deviations from Specification and Requisition

(To be completed during project execution)