drilling into existing bus

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Grouch1980

Grouch1980

Senior Member
Location
New York, NY
Hi all,
Let's say i have a switchboard or a distribution board with no spare switches available. I know we can add an additional switch because the load on the switchboard is pretty low. Am I allowed to drill into the existing bus inside, make a new tap, and place a remote switch on the side of the switchboard? I know this may void the warranty on the board, but the does the NEC allow this?

Thanks!
 
The NEC would allow it if it does not violate the listing of the equipment. I've seen this done many times in old buildings.
 
I know, i've seen it done as well... even in new buildings... sometimes they have to add something and they'll drill into the switchboard. someone brought this up as an NEC isssue, which is why i came here to ask.

how would you violate the listing of the equipment though? if you overdrill the bus?
 
Grouch1980 said:
I know, i've seen it done as well... even in new buildings... sometimes they have to add something and they'll drill into the switchboard. someone brought this up as an NEC isssue, which is why i came here to ask.

how would you violate the listing of the equipment though? if you overdrill the bus?
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Once you drill a hole in the bus there is no way to tell if you have altered the switchboard in a way that may have change it's listing, weakened the bus, changed it's current carrying capacity, etc. It would probably need to be field evaluated by a NRTL after it's done. Now if the bus already had extra holes in it and you attached to them IMO that would be less of an issue.
 
When doing kirk key retrofits, the manufacture would often ship buss bar adapters that bolted to the exsisting buss, But usually I was bringing quite a few cables into the gear, and there would not be sufficient room to bolt enough lugs to the exsisting buss. It also allowed the lugs to be flagged and staggered for better clearance. Possibly the manufacture may have a listed kit to do it that way.
 
I've called for it many times on electrical drawings, whenever needed. Never had an issue. Just came across a contractor who said it's a violation.
 
Grouch1980 said:
I've called for it many times on electrical drawings, whenever needed. Never had an issue. Just came across a contractor who said it's a violation.
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It may or may not be a violation. Some bus comes with instructions on how to drill extra holes if needed. You can also get listed connectors that clamp on to the bus so no drilling required.
 
This is done a fair amount for solar supply side connections and some AHJs have policies requiring field listing, which of course is not cheap.
 
Grouch1980 said:
how would you violate the listing of the equipment though?
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Technically everything you do to equipment, in the field, causes the listing to be violated. The listing really only applies to how the equipment was manufactured.

Your question is really ' does a field modification, like drilling the bus bars, go against what might have been allowed at the factory, thus causing it to be unsafe.
UL says field modifications should be 'judged' by the AHJ for suitability. UL will gladly conduct a field evaluation for a fee.
 
The last time we did this to some gear, the inspector required a letter from the manufacturer stating they approved of the modifications.
 
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