PI: 690.8(B)(1)

[wwhitney]

More ambiguity removal. Cheers, Wayne


(1) Without Adjustment and Correction Factors.

The minimum conductor size with an ampacity not less than the maximum currents calculated in 690.8(A) multiplied by 125 percent.
Exception: Circuits containing an assembly, together with its overcurrent device(s), if any, that is listed for continuous operation at 100 percent of its rating shall be permitted to be used at 100 percent of its rating.

Statement of Problem and Substantiation for Public Input

Clarify that in the case a circuit has no overcurrent devices, e.g. as allowed under 690.9(A)(1), the exception may still be used as long as the rest of the equipment in the circuit is listed for continuous operation at 100 percent of its rating.

 

[jaggedben]

Okay I guess I like it. I've had this thought. I think the difference might be negligible in light of subsection (2).

I had to think a bit to decide if the proposed change achieves the clarification you intend. I still can't decide.

I've always thought the wording didn't quite say what it intended to mean. PV circuits don't typically 'contain' assemblies which include OCPDs. But they might terminate at them. If they 'contain' 100% listed assemblies, but terminate at assemblies with OCPDs that are not so listed, it doesn't seem to me that the exception should apply. But that's the way it's written.

I believe what we're interested in here is:
1) permitting a DC combiner box with OCPDs to be used continuously at 100% of it's rating when so listed
2) not requiring this 125% factor for PV circuits that don't have OCPDs in them

 

[wwhitney]

FWIW, the phrase "containing an assembly . . ." also occurs in (2017) in 694.12(B) and in 705.60(B).

My approach this cycle has been to make minimal edits that attempt to disambiguate things I find unclear. [Personally I think the current language already covers the case of no OCPD, but I can see how it may be read to require an OCPD.] I'm perhaps wishfully thinking that smaller changes will be more acceptable to the CMPs.

But if you have thoughts on how to rewrite the section more broadly to be clearer, please do put in your own PI. It's pretty simple once you get past the interface, that's why I have over 20 PIs now.

If I wanted to do a more extensive rewrite, a first draft would be:

Exception: Circuits containing only equipment, together with any overcurrent device(s), that are listed for continuous operation at 100 percent of their ratings shall be permitted to be used at 100 percent of its rating.

Cheers, Wayne

P.S. The big question for me is whether a typical PV string inverter's DC side is "listed for continuous operation at 100% of its rating." And I guess also the PV panels themselves. If so you could omit the 125% continuous factor on DC string ampacity. Although I haven't done enough computations to tell if that would typically allow downsizing conductors, or if the conditions of use factors would dictate no reduction in size.