Table of Contents

  1. Summary
  2. General
  3. Incoming Feeder and Tie Breakers
  4. Bus Bar from Main Switch to Horizontal Bus Bars
  5. Horizontal Copper
  6. Bus Bar System Vertical Sections
  7. Outgoing Units
  8. Earthing
  9. High Potential Test
  10. Insulation Measuring
  11. Meters and Protective Relays

1. Summary

Before the low voltage switchgear is ready for shipment the vendor shall make suitable tests to establish to the satisfaction of owner’s representative that all equipment, devices, protection relays and wiring have been correctly installed and are in satisfactory working condition and operable as requested.

All tests shall be made in accordance with the nationally recognized standards stated in the requisition.

The entire installation shall be constructed so as to provide maximum safety. Even if more provisions than required by law will be necessary, it will be vendor’s responsibility to include these provisions.

Prior to testing, switchgear shall be dust-free and thoroughly cleaned of all waste material.

The switchgear vendor shall take care that all necessary test equipment will be available in the factory or at field.

2. General

The switchgear shall comply with the following requirements:

Is the switchgear of the draw-out or the nondraw-out type:


Is the incoming feeder a cable connection or a busduct connection

cable/busduct connection

Is the switchgear for indoor or outdoor use:

indoor/outdoor use

Short-circuit current of the installation:

KA rms
KA peak

Time short-circuit current of the installation:


Maximum nominal current:


1. copper connection incoming feeder


2. main breaker(s)


3. horizontal busbar system


4. tie breaker


Nominal voltage:




Language to be used on the name-plates for operating instructions and outgoing circuits:


Language to be used for maintenance instructions:


What is the color of the outer side of the switchboard:


Dimensions of the installation:

length mm

width mm

height mm



What are Company’s numbers of the drawings according to which the switchgear will be inspected:






Who will take care of the erection at site:


Is the busduct connection between the transformer and the switchgear finished

and by whom will this connection be installed:

1. busduct connection is not included in the supply.

2. busduct connection

3. installation of the busduct connection by supplier/Company.

4. no busduct connection

The frame which shall be cast-in or connected to the concrete floor of the substation and will be supplied by:

1. supplier of switchgear

2. Company

In case the frame will be supplied by the vendor, have the frames already been shipped:


The required height and width of the substation door(s) are (inclusive of 4” rolls):





Take care that everything will be new and unused.


Is a crane necessary for hoisting the switchgear into the substation:

If yes, contact the Field Engineer for provisions to hoist the switchgear into the substation.


The use of plastic partitions for screening is not permitted.

Screening shall be by Pertinax sheets or equivalent material.

Equivalent material may only be used after approval by purchaser.



Pay attention to the wiring, relays, terminals etc.; they must be coded in accordance with the drawings.

The wiring shall be coded so that after disconnecting it can be reinstalled without checking at the right terminals.


What are the colors of the wiring:


What are the colors of the wiring:



3. Incoming Feeder(s) and Tie Breaker

There must be sufficient space for connection of incoming feeders (check one line for number).


Check whether the neutral is mounted on the right side, viewed from the front.


Check the diameters of the holes for the connection bolts of the busbar with regard to the width of the busbar. Holes must be too big (DIN 43673).

flat copper bar, width


fastening holes, diameter



It must be impossible to touch the incoming copper when the door is open (pay attention to the Pertinax sheets).


Check whether the nominal current of the breaker is sufficient with regard to the transformer or switchgear rating.

current of breaker


current of power transformer


Incoming feeder and tie breaker shall be suitable for the dynamic short - circuit


KA peak

current of the transformer and thermal short current of


KA rms


Check whether the outgoing or incoming copper is directly mounted above the arcing chutes.

(This is not permitted. The ionized air must be able to rise freely and may not introduce a short circuit).

Make sure that there are no obstacles which can hamper the gas flow on the upper and front side.


When protective relays are installed on the breaker, check the current and time settings.





When an inverse current/time relay is used, ask for relay curve.





Type, number and brand of relay(s):



It shall be possible to operate the main breaker with the compartment door closed (manually and electrically)


Check whether arcing chutes are undamaged and uncracked. Try to remove the arcing chutes from the breakers.

This must be possible without touching any obstacles.


Wires going from the main busbars to fuses (for example for closing the main breaker) may not touch other wiring or steel constructions and must be short as possible.


Check especially the bolt connections of the copper bars to the main breaker, even if something shall be removed. Check the number of bolts and the bolt diameters with regard to the mounting busbar. Check also the tensile strength of bolts.


Check the distance of the busbars with regard to each other and with regard to earth (neutral). The distance shall be at least 2 cm.


Check whether there is a link in the neutral of the incoming feeders.


The presence of a link shall be clearly indicated with a nameplate.


Check especially that the air circulation along the breaker is not obstructed. This is for cooling of the breaker. (Wrong positioning of the Pertinax plates.)


How is the incoming breaker controlled:


Is the transfer from one feeder to another automatic or manual:

1. manual

2. automatic

3. no automatic

4. one feeder


Are both feeders in parallel while transferring:

1. manual transfer


2. automatic transfer:


What is the position of the tie breaker in normal operation:

1. open

2. closed

3. no tie breaker

Are feeder breakers and tie breaker of the draw-out type:

Check especially the draw-out contacts when the breakers are of the draw-out type.


Are feeder breakers and tie breaker interchangeable:


Can one feeder handle the total load:





Are protective relays installed on the tie breaker:


Is the coupler a breaker, link or a load switch:

breaker/link/load switch

When a link is installed, an ampere meter shall be installed:

Ampere meter: yes/no

Close the feeder breaker and try to withdraw the switch in the closed position.


Also try in the opposite sequence.

Take the feeder breaker out of the switchgear, close the breaker and try to insert the breaker.

Before the main contacts touch each other the breaker will be switched off.

Even when it is not possible to insert the breaker in the closed position, this will be an acceptable construction.


When the feeder breaker is inserted, but is in the off-position with charged springs for fast closing, the breaker must be able to unload automatically, or further movement of breaker must be prevented.



4. Busbars from Main Switch to Horizontal Busbars

Vertical busbars from main switch to horizontal busbars must have the same cross-section as the copper of the incoming feeders. Is this so?


It shall be impossible to touch this copper, even with an open door (screening with Pertinax plates).


If there are lids instead of doors, screening of the busbar is not necessary. The lids must be fastened with captive screws. Fastening the lids with toggles is not permitted.


Check the voltage distances with regard to each other and with regard to earth. Take into account where these distance are found.

Take care of the bolt connections in the busbar.


Check the bolt connections with a torque wrench.

This is applicable to the entire busbar system.

Check whether all bolts are easily accessible.


If current transformers are applied, take care of the current direction (current goes always from K to L).


Check the following characteristics of the current transformers:

1. ratio:


2. class:


3. output:


4. excess current:

N =

5. suitably for short-circuit current or during a time of:

KA peak
KA rms
1 s.

The wiring connected to the secondary side of the current transformer inclusive of earthing shall be at least 4 mm2.



The busbar shall be marked with painted dots in the color specified in the requisition. This shall be done at different places in the switchgear.


Check whether there is a partition plate between the vertical copper and the horizontal copper. If there is no partition plate, check whether the horizontal copper has partition plates on both sides of the incoming feeder panel.


If parallel buses are used, check whether there are copper pieces and check how they are fastened; bolts screwed in the copper of the busbar are not acceptable.


Spring washers shall be placed under the nuts of the fastening bolts of the buses.



5. Horizontal Copper

The horizontal copper must have the same cross-section through the entire switchboard.


What is the cross-section of the horizontal copper with regard to the incoming feeder panel?

Check also the cross-section of the neutral.


Is the horizontal busbar compartment separated from the vertical compartments?

(Partition plates between horizontal copper and outgoing vertical copper)


Check especially the distance of the busbars with regard to earth where the angle iron of the vertical sections have been mounted.


Insulation tape or Pertinax to improve the situation at certain spots is not acceptable. This is applicable to the entire switchgear.


Check especially the bolt connections. The bolt has to come just through the nuts. This applies to the entire busbar system. Check whether all bolts are easily accessible.


Check whether the supporting of the busbars is sufficient. A strip of insulation material mounted on the top of the insulators to improve the maximum allowed force in acceptable.


The busbars at the ends of the switchgear shall be finished in such a way that an extension of the switchgear is possible without any further mechanical handling.


Check the bolt connections of the horizontal copper with the downgoing vertical copper. Take care of possible torques. This occurs on those places where an angle is in the copper and no support is placed in the angle, because torques reduce the short-circuit capacity. This applies to the entire busbar system.



All high-tensile strength steel bolts, nuts and rings shall be corrosion-proof.


Check the interconnections of the horizontal busbars. With how may bolts are they connected? What are the sizes of the bolts? What are the dimensions of the copper overlapping?


Threading in the main rail system is not acceptable.


Top of insulators may not be used for interconnections of the busbar system.


The insulators on the supporting iron shall be installed so that also the outer rim of the insulator bottom is supported and the insulator is supported completely on its bottom surface.


When insulators are fastened with a bolt, it is not permitted that the insulator is turned to be fastened, but the bolt shall be screwed into the insulator. Pay attention to welded tap ends; these are places where such things happen.


The insulators shall be free of paint, dust and damage.


When partitions are used to support the busbar, check whether the copper is firmly enclosed by the supports and check whether the partitions are fabricated of nonhygroscopic material.


Check whether the bolts of the steel top cover do not come too close to the busbars.



6. Busbar System Vertical Sections

Check the dimensions of the vertical copper and the supporting of the vertical copper:

dimensions copper

x mm

distance between two insulators in the length and width

It shall be impossible to touch the vertical copper (even not from an adjacent panel or when the units are drawn-out).


Check especially the lower part of the copper. This must be protected so that ionized air cannot flow into adjacent panels.


Check the connections between the vertical copper and the various units.

Check especially the distances, supports and bolt connections.


If there is a copper connections between vertical copper and a unit, it must be screened with an insulating material, which is fireproof (no tape or similar).


When working in an outgoing panel, it must be absolutely impossible to touch any live parts, even not the live parts of an adjacent unit.


It shall always be possible to insert the outgoing cables without touching the busbar system.

Installation of the cables will be done energized busbar system.


The maximum fuse rating of the back-up fuse may not be more than 200 A.

It is allowed to provide the units behind that back-up fuse with fuse holders and fuses of the screw type.


Check whether the vertical sections are totally enclosed:

Check also the bottom.

totally enclosed: yes/no

Check whether soft packing rims are used between the vertical sections to avoid openings.



7. Outgoing Units

A short circuit in a unit may never cause a complete busbar short circuit. This shall be checked carefully. The most dangerous place is the connection between unit and busbar system.


Before the main and auxiliary contacts touch each other, there must be a good earth connection between unit and enclosure, so that there can never be a voltage difference between unit and earth, not even under the most unfavorable circumstances. Earthing of the unit must be checked carefully.


Check especially the draw-out contacts and connections to the circuit part. Wrong insertion may never cause a short circuit or a damage to the contacts and/or pins.


If electrical components are mounted on the doors, a flexible connection between door and fixed part shall be installed.


All units of the same type shall be interchangeable. Some units shall be drawn out to check the wiring at the units.


Unit compartment shall be totally enclosed and preferably be made of metal.


The connection of the primary side of the fuses and the contacts at the back of the draw-out unit shall be at least 25 mm² and shall run free of other wiring and steelwork.


Partitions of insulating material shall be placed between the fuses, sticking out above the fuses. This is also applicable to the draw-out units to prevent a short circuit at the primary side of the fuses. Partitions must continue at the upper side.

The air distances between the live parts at the primary side of the fuses shall be made as long as possible. A short circuit at the primary side of the fuses means a short circuit at the main busbar system (full-circuit capacity).


Check the fuse holder rating with the fuse concerned. This shall be an internationally standardized fuse holder and fuse of the knife-type.

Check type of fuse (gL preferred):


In connection with the short-circuit capacity of the transformer pay attention to the highest permissible short circuit of the fuse.


Screw-type fuses may only be used behind back-up fuses of maximum 200 A.


For screw fuses only the E27 type is acceptable.


The location of the components in the unit shall be so that ionized air around a contactor or a short circuit within the unit can never cause a short circuit at the primary side of the fuse. The fuse must always interrupt the short circuit of flash-over.

This is very important!


Try to make a short circuit with the fuse remover.


Check the relation between the fuse rating and the thermal relay rating. This is to prevent damage of the thermal relays in case of short circuiting. This should only be done according to leaflets of thermal relay manufacturer and not according to any Company or vendor’s drawing!



Check the adjusting devices of the thermal relays.


Check whether the rating of the smallest contactor is 20 A. It is not allowed to use relays or auxiliary relay in the primary wiring of the motor circuit.


The connections in the unit shall be made with flexible wires. Cable lugs shall be of the crimpit type. Soldering connections are not acceptable.


Wiring for protection and transfer circuits shall be numbered at both sides. Wiring, mounted in the units, must be numbered at the terminal blocks so that it is not required to measure the wiring before reconnecting the wires to the terminals.


Control fuses may be of the E27 type, if placed behind main fuses. If MCB’s are used, check characteristic (L).


It shall always be possible to check the current of the unit with a hook-on ampere meter in order to adjust the thermal relay. The wiring must allow space for that.


A number of units of different types shall be checked on their proper electrical working. If any defects are found all units shall be checked.


It shall be possible to reset the thermal relay from the outside of the unit.


The lamp holder shall be made of copper to prevent sticking of the lamp at high temperature.


The terminals shall be of a good quality and preferably be made of thermosetting material and not of porcelain.



Check the quality of the short-circuit connection at the terminals. This in connection with short-circuiting of the current transformers.


The outgoing cables of the various units shall be supported. The supporting saddles shall be supplied by the manufacturer of the switchgear.


Check whether fuse ratings, contactor rating, thermal relays, etc. comply with the drawings. Don’t forget the spare units. These shall be installed completely as marked on the drawings. Check also the space units.

It shall not be necessary to switch off the switchgear while equipping the space unit.


Terminals carrying different voltages shall be separated by means of partitions, which totally stick out of the terminal.


Take a draw-out unit of the fuse-switch type from the switchgear and try to “draw-in” the unit in the switchgear again with the switch in the “on” position.


Also try in the other way around. The unit is installed in the switchgear. Switch “on” and try to take it out of the switchgear.



8. Earthing

There shall be an earth bar over the entire length of the switchgear. It shall have a dimension of at least 25 x 5 mm.


The copper shall be as long as possible to minimize the number of connections.

The earth bar shall be mounted directly to the steel structure and so that each vertical part has at least one connection with the main earth bar.


At the end of the horizontal earth bar two holes shall be drilled for connection to the external earth system (Ø 13 mm).


If there are terminals below the outgoing groups, the main earth bar shall have earth screws: for each cable at least one.

The connection shall be so that it is possible to earth the lead sheath as well as the earth conductor of the cable.


When the cables are connected directly to the units, there will also be an earth bar mounted along the units.

It is not acceptable that the cables are stripped all over the height of the installation for earthing the cable at the bottom at the main earth bar.


The main breakers shall have a direct copper connection with the main earth bar.


When the switchgear has a bus duct, there will also be an earth bar inside the bus duct.


All parts of the bus duct will be connected to the earth bar. There will also be an earth bar between switchgear and bus duct.



The secondary side of the current transformers shall also be earthed. Looping of an earth wire is not acceptable. The connection will be at least 4 mm².



9. High Potential Test

Check whether the installation is ready to be put into operation; so all units, fuses, switches, etc. shall be present and the switches shall be in the “off” position.


High potential tests shall be 2500 V for 1 minute and applied between:

  1. phase to phase
  2. phase to neutral
  3. phase and neutral to earth

If certain components such as coils of contactors, motors of breakers, current transformers, voltage transformers, etc. look strange the components shall be tested in the following way:

  • coils
  • small motors of breakers
  • current transformers
  • small transformers

The control fuses of the meters and relays shall be removed.

The high voltage test set shall have a minimum capacity of 3 KVA.

1000 V 1 minute

1000 V 1 minute

3000 V 1 minute

1500 V 1 minute


10. Insulation Measuring

Insulation resistance will be measured after the high potential test. The resistance will be measured:

  1. phase to phase
  2. phase to neutral
  3. phase and neutral to earth

If possible, test the meter with a calibration resistance.


The resistance shall be at least 10 MW if the installation is in dry condition.

If the humidity is very high the switchgear must be dried before measuring.


Make a connection between one phase and earth and check whether the megger is indicating zero.

This is to be sure that the entire switchgear is tested.


The insulation shall be measured with a 500 V megger (or higher).



11. Meters and Protective Relays

The working of directional relays shall be checked very carefully.


The final test shall be performed in the field.

Check whether the wiring complies with


vendor’s data:

directional relays testing


The same is applicable to the Kwh

KWh meters tested:


meters and the power factor meters:

power factor meters tested:


These are directional instruments and the correct working depends upon the

KWA meters tested:


right polarity of the connections.

KW meters tested:


Check whether the voltage on the meters and relays is correct. The same is applicable to the current. It may be possible that the current coils need be switched in parallel or in series.

This is indicated on the relays.


Are the relays of the draw-out or nondraw-out type.

draw-out/non draw-out

In how many phases are the directional relays placed:


How are the Kwh meters connected: