705.12(B) feeder tap on busbar

[electro7]

I have a couple commercial 3 phase PV projects and was wondering if I could bolt on to the busbar on the load side of the main breaker, following the feeder tap rules, to a fused disconnect- instead of landing a breaker in the MSB? Any thoughts? Would this fall under the 705.12(B) feeder tap rule if I bolt on the opposite end of the busbar?

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[jaggedben]

Why don't you want to use a breaker?

I don't see any violations if tapping from the opposite end from the main breaker, but you still have to meet the 120% rule. Other spots on the busbar would require you to protect the downstream portion of the busbar which would no doubt be problematic. In my opinion there is no way to use the feeder tap rules to get around the busbar rules.

 

[electro7]

Yeah, still abide by the 120% busbar rule.

The breakers would add approximately $4000 to the job, and if I don't need them because I'm using the fused disconnect, then I'd rather save the money. Plus, the labor to move around other breakers to get to the opposite end of the busbar when I maybe don't need to if I bolt to the bussing.

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[electrofelon]

I assume this is a switchboard. In some code cycles the bus bar rules do not apply to switchboards. You want might want to make sure your ahj is cool with how you will be tapping the bus bar

 

[electro7]

Yes, it's a switchboard. I am checking with the engineer about it as well, but I'd be bolting through existing holes, so there is no drilling or tapping busbar.

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[pv_n00b]

You can with a couple of things to look out for:

• If the SWBD manufacturer does not provide instructions that say you can use the specific holes you want to use for a tap then you are going outside the UL listing. The AHJ now can either approve it, reject it, or require that you have an NRTL do a field listing. For an NRTL field listing the NRTL can accept or reject what you want to physically do to make the interconnection.
• Prior to 2020, NEC 705.12(B)(2)(3) did not provide guidance for interconnections other than to panelboards. Most people have assumed it can be done under engineering supervision. Some people default to using 705.12(B)(2)(3) anyway even though the NEC states it only applies to panelboards. In the 2020 and later versions, 705.12(B)(3)(5) specifically allows that it can be done under engineering supervision.

 

[electrofelon]

You can with a couple of things to look out for:

• If the SWBD manufacturer does not provide instructions that say you can use the specific holes you want to use for a tap then you are going outside the UL listing. The AHJ now can either approve it, reject it, or require that you have an NRTL do a field listing. For an NRTL field listing the NRTL can accept or reject what you want to physically do to make the interconnection.
• Prior to 2020, NEC 705.12(B)(2)(3) did not provide guidance for interconnections other than to panelboards. Most people have assumed it can be done under engineering supervision. Some people default to using 705.12(B)(2)(3) anyway even though the NEC states it only applies to panelboards. In the 2020 and later versions, 705.12(B)(3)(5) specifically allows that it can be done under engineering supervision.

Right, definitely want to get the inspector's blessing on this first. I had to do this once and got the inspector there before I started anything, he said he was fine with listed lugs on existing holes. Obviously YMMV.

 

[electro7]

Thanks guys

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