Feed through panels

[ggunn]

In the case where the utility feeds a feed through panel, and we want to land a PV breaker in the panel on the other end of the feed through conductors, the feed through conductors connecting the panels are essentially an extension of the busbars and are therefore subject to the 120% rule just like the panel busbars, wouldn't you say? Assuming that the conductors have a 90 degree insulator rating, the 90 degree rating derated for conditions of use if necessary of the feed through conductors would be the number to use in that calculation, correct? There are no taps on the feed through conductors between the panels.

 

[jaggedben]

First, correct me if I'm not understanding correctly. You have two panels, the first one feeds the second through feed through lugs, and you want to put a PV breaker in the second one at the opposite end from where it's fed. Correct?

Next question: Which code cycle?

Under 2011, I would say yes, those conductors between the panelboards could be subject to the 120% rule. 705.12(D)(2), IIRC, says 'busbar or conductor'. A lot of AHJs don't enforce it but some do.

Under 2014, I would say no. They removed that language and the 120% rule now applies only to a panelboard. The conductors between are a feeder fed from the opposite end.

 

[pv_n00b]

I consider those conductors an extension of the busbar, just as the conductors feeding an MLO panel are extensions of the busbar for 705.12(D)(2)(3) purposes. This only is a problem where for some unknowable reason someone put in a conductor with a rating less than the busbar.

 

[jaggedben]

I consider those conductors an extension of the busbar, just as the conductors feeding an MLO panel are extensions of the busbar for 705.12(D)(2)(3) purposes. ...

I just don't see how the code says that. 705.12(D)(2)(2) is for feeders. 705.12(D)(2)(3) is for panelboard busbars. No one would ever call a feeder feeding an MLO panel an extension of the busbar if no backfeed were involved. Why should it be different when there's a backfeed? To my mind, the changes made to 705.12(D) in the 2014 code were intended to eliminate these sorts of interpretations.

 

[Davi]

Solar prep at main or subpanel?

Solar prep at main or subpanel?

I have ran my pipe to the subpanel and not to the main for power. Is this a violation?

 

[pv_n00b]

I just don't see how the code says that. 705.12(D)(2)(2) is for feeders. 705.12(D)(2)(3) is for panelboard busbars. No one would ever call a feeder feeding an MLO panel an extension of the busbar if no backfeed were involved. Why should it be different when there's a backfeed? To my mind, the changes made to 705.12(D) in the 2014 code were intended to eliminate these sorts of interpretations.

I have to agree. Up through the 2011 NEC they treated the bus and feeder the same. I never really agreed with that but played along, maybe I am just stuck in that mindset since we are still under 2011 in CA. As long as the feeder is rated for the PV back feed current, as any conductor should be, it is good.

 

[jaggedben]

I have ran my pipe to the subpanel and not to the main for power. Is this a violation?

No, not by itself. But both the sub and main have to be properly rated if you do this.

 

[jaggedben]

I have to agree. Up through the 2011 NEC they treated the bus and feeder the same. I never really agreed with that but played along, maybe I am just stuck in that mindset since we are still under 2011 in CA. As long as the feeder is rated for the PV back feed current, as any conductor should be, it is good.

I've been training my designer on the 2014 code and today I had to remind him we don't get to use the new rules for another 4+ months.

 

[Davi]

No, not by itself. But both the sub and main have to be properly rated if you do this.

Im running a track homes for detached home and we are putting in solar prep. Inspector told me that my conduit needed to be at the main. So i look up the code and found out i was fine in the subpanel.

 

[ggunn]

Im running a track homes for detached home and we are putting in solar prep. Inspector told me that my conduit needed to be at the main. So i look up the code and found out i was fine in the subpanel.

So long as you comply with 705.12(D)(2)(3) in both panels, that is correct.

 

[jaggedben]

Some inspectors in California might still require a continuous grounding electrode conductor (#8) even for transformerless inverters. Since your profile says San Jose I'll mention Milpitas as one that's a stickler for the grounding requirements. However if you have a subpanel in a detached building then you should already have a grounding electrode there and your inverter GEC, if required, can terminate there.