Sorry, I don't see the difference between 240.21(B)(1)(1)(b)'s text "the overcurrent protective device at the termination of the tap conductors" and 240.21(B)(2)(2) text "the tap conductors terminate in a single circuit breaker or a single set of fuses". I would think any configuration would that meets one description meets the other, and vice versa.
Enough difference for someone to say that (1) requires conductors to a fusible disconnect to be sized for the rating of the disconnect and not for the rating of the fuses.
Still not seeing it. Let's say that I don't want to use the "rating of the equipment containing an overcurrent device(s) supplied by the tap conductors" clause in 240.21(B)(1)(1)(b). Then the rest of 240.21(B)(1)(1)(b) becomes:
I am saying the "or" does work that way. It does not give the installer a choice. That choice is made by the type of equipment being installed.
Presumably you mean "does not work that way."
That language makes it very clear that once you install an OCPD in the equipment, the tap conductor can be sized to that OCPD. I still don't think that the current rule is completely clear, however the intent is to permit the tap conductor to be sized to the OCPD in the equipment as I said in post 30.
The intent is that the calculation in 240.21(B) - e.g. 1/10 for a 10ft tap or 1/3 for a 25ft tap - is performed on the sum of the feeder OCPD and 125% of the interconnected source current. e.g. 100A feeder breaker, 32A solar output, and a 25ft tap would require (100+(32*1.25))/3= 46.67A ampacity for your tap conductors. In many cases your minimum requirement for the output will still govern.
In general, being more conservative than what the NEC requires is always allowed, although there is the occasional inspector that does not understand this. One case we ran into was a guy who insisted on failing us on our inspections if the minimum PV interconnection breaker was 35A and we used a 40A breaker with appropriately sized conductors. His "reasoning" was that the inverter "will never trip that 40A breaker". Well no, of course not. Duh.
Well his reasoning was off, but I would agree with him that you cannot just put as large a breaker as you want on a piece of equipment even if the conductors are sized to match. There are sections in the NEC that dictate max OCPD size, and then of course there are manufacturer instructions which often provide a max size. Even though an inverter doesnt "use" current, I could see a max size being part of the testing/rating/listing process and a certain size OCPD could protect it from worse or more catastrophic damage if there was an internal fault. Sort of like how something like an ATS has a variety of different OCPD options and the characteristics of those OCPD's such as clearing times can effect the allowed max size of that OCPD.One case we ran into was a guy who insisted on failing us on our inspections if the minimum PV interconnection breaker was 35A and we used a 40A breaker with appropriately sized conductors. His "reasoning" was that the inverter "will never trip that 40A breaker". Well no, of course not. Duh.
Correct. We were building a lot of smaller load side connected resi PV systems using microinverters, and we wanted to standardize the interconnections to 40A breakers so that the installers wouldn't have to carry around a lot of different breaker and conductor sizes. This guy also wanted us to downsize the individual breakers in the AC combiners where fewer than the maximum number of microinverters was on a branch. He was convinced that the OCPD was there to protect the conductors from the inverters.
It was not a factor in these cases. The OCPD in question was between the AC combiner panel and the service and not directly connected to the (micro)inverters. I guess it could have been a 4000A breaker without any issues, but of course it was not.
Once again, this has no bearing on the case I cited. The OCPD in question was between the service and the AC combiner and not directly connected to any inverter. It was not in violation of either the NEC or the manufacturer's specifications.
