Load Side Connection on Bus Duct Through plug-in unit?

[Frank6172]

Hi All,

The roof top level electrical room has a 800A bus duct protected by a 600A breaker in the basement electrical room and we have 120A total output current from all inverters. Per 2017 NEC 705.12 (B)(2)(3)(a) 1.25x120+600<800A so we should be able to do load side connection on bus duct. However, I have 2 questions: (1). Does plug-in unit on the bus duct have OCPD? The rooftop level electrical room is very tight in terms of space so I couldn't install any fused disconnect there with proper working space clearance. (2) Is the plug-in unit good for backfeed? here is the nameplate of the bus duct below.

 

[jim dungar]

In general a lugs only kit for the bus duct would be at thr full rating of the duct, so it could be significantly larger than a smaller OCPD. But check with your manufacturer.

 

[jaggedben]

... Per 2017 NEC 705.12 (B)(2)(3)(a) 1.25x120+600<800A so we should be able to do load side connection on bus duct.

Your listed busway (art 368) is really considered a wiring method, not distribution equipment. So I think you should be thinking of this as a feeder tap. So it's 705.12(2)(1)(a) that you comply with (math is the same). 705.12(2)(2) is a bit odd in the 2017 code and can be read as requiring your tap conductors to be rated for at least 247.5A, that is (600+120×1.25)×.33, if doing a 25ft tap. But you can use the tap rules so if you can do a 10ft or 25ft tap to a fused disco outside the electrical room you should be good. That is, you don't need the PV OCPD closer than that.

(2) Is the plug-in unit good for backfeed? here is the nameplate of the bus duct below.

I'm not familiar with busway connections but assuming it's just a conductor termination and doesn't contain a protective device then it's certainly suitable for backfeed.

 

[pv_n00b]

FPE has been out of business for awhile. Luckily this company provides parts: www.fpeparts.com
You might be able to get a bus plug switch or an OCPD to connect to the bus. Contact FPE Parts and see what they can do for you.
If you get a bus plug switch then treat the connection as a tap in 240 and 705. That's going to be a problem if you can't get to a fused switch close by. If you can get an OCPD then your utility is still probably going to requires a fused switch to have the visible blades.
If you get an OCPD then the bus duct bus can be treated as a really long bus in a SWBD. I would apply the same rules from 705.

 

[pv_n00b]

Your listed busway (art 368) is really considered a wiring method, not distribution equipment. So I think you should be thinking of this as a feeder tap. So it's 705.12(2)(1)(a) that you comply with (math is the same). 705.12(2)(2) is a bit odd in the 2017 code and can be read as requiring your tap conductors to be rated for at least 247.5A, that is (600+120×1.25)×.33, if doing a 25ft tap. But you can use the tap rules so if you can do a 10ft or 25ft tap to a fused disco outside the electrical room you should be good. That is, you don't need the PV OCPD closer than that.

While a busway is not distribution equipment, feeders and branch circuits taken off a busway with OCPD as in NEC 368.17(C) are treated as feeders and branch circuits from distribution equipment and not as tap conductors. I think it's reasonable to treat them the same as a connection to a SWBD bus through an OCPD.