4160 V SWITCHGEAR

[bobziva]

4160 V switchgear for industrial purpose should be extended. Instead regular extension ( new cubicles/ extension of buses),client want to install new 4160 V switchgear, connected by H.V. cables with existing switchgear. What we have after that ?
old SWG, new SWG plus cables connecting these two switchgears. At one side of H.V. cable( old switchgear)NO BREAKER, at another side ( new switchgear) BREAKER exists.
I THINK THIS SOLUTION IS NOT ACCEPTABLE, BUT CLIENT SAID THAT IS NORMAL FOR INDUSTRIAL AREA.
System is radial i.e. single transformer.

 

[peebee]

So long as your new bus & connecting cables are rated the same as your source gear overcurrent protection, you're all set.

The NEC tap rules (see Article 240) might permit undersizing the taps, too, so long as your cables are less than 10 or 25 feet.

 

[RajT]

The client is quite correct in his recommendations.

 

[peebee]

My biggest concern would be regarding how you plan to accomplish the bus tap at the existing switchgear.

I admit, it seems to be common practice to simply drill a hole in the bus and bolt a lug up to it. And it is clear that the NEC permits conductor taps, which would include bus taps.

However, I am under the impression that this would violate the UL listing of the existing switchgear unless the drilling was performed by the original manufacturer or other party certified to make such modifications. Violation of UL requirements should not be taken lightly, as this could potentially expose the owner, engineer, and contractor to liability issues; moreover, there is a much higher probability of potentially life-threatening switchgear failure due to a poorly executed modification when performed by an untrained, uncertified electrician rather than a certified switchgear manufacturer.

I have not personally reviewed the UL requirements -- and unfortunately, they are somewhat expensive. However, I have been trying to research this in the meantime. Any input on this issue from this forum would be appreciated.

In the meantime, I would STRONGLY suggest that you specify that any modifications to the existing switchgear be made by the original manufacturer. And don't be too surprised if the original manufacturer declines to make such a modification. In that case, I would STRONGLY suggest that you send a CYA letter to your client recommending against them permitting an electrician to make such a modification.

On the other hand, if you can find a switchgear manufacturer (original or 3rd party) who is willing to issue a letter re-certifying that the modifications are in compliance with UL requirements, I would have no issue whatsoever with the installation you originally described. Your only concern is to make sure that proper overcurrent protection is provided for the cabling; either the typical upstream overcurrent protection, or alternately, downstream overcurrent protection as permitted by the 10-foot and 25-foot tap rules.