MV cabinets busbar earthing switch

[radug]

Dear all,

For the design of 6.6kV cabinets, an engineering subcontractor is recommending to add a cabinet with an earthing switch so that in case that maintenance work has to be done in the cabinets, the busbars can be earthed before performing the Works.

Cabinets are metalclad type and all circuits use withdrawable type circuit-breakers with the corresponding earthing switch.

The Project is located in IEC world, although I would also like to know which is the current practice in ANSI/NEMA world.

Is this busbar earthing switch mandatory? If so, in what standard is it requested? Is it only recommended.


Thank you in advance for your help.

 

[7anoter4]

I don’t know a standard where the busbar grounding switch it is required. May be an utility requirement in some regions. I wonder what is the way to safety check the busbar is not energized before grounding.
However,NESC-National Electric Safety Code [ANSI/IEEE C2] Rule 123. Protective grounding
C. Provision for grounding equipment during maintenance
states:
“Electric equipment or conductors normally operating at more than 600 V between conductors, on or about which work is occasionally done while isolated from a source of electric energy by disconnecting or isolating switches only, shall be provided with some means for grounding, such as
switches, connectors, or a readily accessible means for connecting a portable grounding conductor."

 

[radug]

Thank you 7anoter4,

The question is that I never saw a busbar earthing switch in MV cabinets, only earthing switches in each of the circuits.

 

[Marmite]

What make/type of switchgear is this Radug? Often switchgear with withdrawable circuit breakers has a transfer earthing capability where the breaker can be racked into an alternative earth position for busbar and feeder earthing.
To work on the busbars to perhaps extend the board, or circuit breaker busbar spouts would require the busbars to be earthed. That doesn't necessarily mean you need a local busbar earth switch on the board. Depending on how the switchgear is interconnected to the remaining network and the safety rules and local operational practices in use, it may be possible to apply an earth at an adjacent substation via a feeder, or even via portable earthing leads applied to the busbar spouts applied after first proving dead. However, it is always preferable from an operational safety perspective to apply the first earth via a suitably rated switching device.

Regards
Marmite

 

[desertfox]

Hi

A switchboard might have a live feed onto its busbars from another remote switchboard and so this live feed would normally be isolated at the remote switchboard circuit breaker.
If your working on the busbars then obviously the remote live feed breaker needs isolating, now the busbar earthing switch would protect people working on the said busbars, should the remote isolating circuit breaker be accidently put back into service.

Hope this helps