Photovoltaic Disconnects

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Typically with a PV installation you have multiple combinations of solar arrays all on one roof or different sections of the roof. The positive and negative leads from each array (described in the 2005 NEC as the PV source circuits) are brought into what we call a "combination box", where multiple leads of the ungrounded conductors (positive) are combined via DC breakers onto a bus bar. This bus bar will have a main lug where a larger AWG conductor takes all of the combined amperage from each array and feeds the main DC breaker typically located within the same enclosure as the inverter. The cicuit between the combination box and the inverter is referred to as the PV output circuit. 690.14(C)(1) states ....the PV disconnecting means shall be located at a readily accessible location........ Since I have a primary DC breaker for the PV output circuit located within the same enclosure as the inverter, and the inverter is located within "a readily accessible location", does the 2005 NEC allow me to mount the combination box on the roof next to the arrays??
 

George Stolz

Moderator
Staff member
Hello, neighbor! :)

This Article in the code is very sloppy, because they use the requirements that apply to service conductors to cover these conductors as well. So, in essence, they expect you to run your conductors along the outside of the house, down the wall to a readily accessible location, so that the DC conductors can be instantly disconnected. Then you proceed to the inverter/batteries.

The utter folly of this is, both sides of the disconnect will still be energized, since you have the sun on one side and the batteries on the other. So, treating these conductors as highly dangerous service conductors is a bit odd.

Or, you could keep your conductors outside the building by one of the methods in 230.6, but from the roof, this is probably more trouble than it's worth.

IMO, technically speaking, that's what you're supposed to do. But before you do anything, I would get the AHJ's opinion on this, because with the wording and oddities in this article, you're guaranteed to get more than one answer to your question, and their answer is the one that counts. Where are you doing the work?
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Hydro, a word of warning: those panels put out a lot of power any time they are illuminated. Treat them, and their conductors, like you should any hot service feeder.
 
georgestolz said:
Hello, neighbor! :)

This Article in the code is very sloppy, because they use the requirements that apply to service conductors to cover these conductors as well. So, in essence, they expect you to run your conductors along the outside of the house, down the wall to a readily accessible location, so that the DC conductors can be instantly disconnected. Then you proceed to the inverter/batteries.

The utter folly of this is, both sides of the disconnect will still be energized, since you have the sun on one side and the batteries on the other. So, treating these conductors as highly dangerous service conductors is a bit odd.

Or, you could keep your conductors outside the building by one of the methods in 230.6, but from the roof, this is probably more trouble than it's worth.

IMO, technically speaking, that's what you're supposed to do. But before you do anything, I would get the AHJ's opinion on this, because with the wording and oddities in this article, you're guaranteed to get more than one answer to your question, and their answer is the one that counts. Where are you doing the work?
I have had lunch with the AHJ, and they do not know either. In fact, they referred me to this web site to ask the question. I do not know what you mean by IMO...........

Here is the rub.....I already have one main DC disconnect at one "readily accessible location" down by the meter, located within the grid-tie inverter. My question is in regards to another DC disconnect (combination box) wired "upstream" of my main DC disconnect that I would like to keep on the roof.

As you have pointed out, even though you kill the DC feed to the inverter, the line side of this disconnect is still hot, typically with 300+ volts DC. The only way to truely kill the DC power genenerated from the panels is to throw a blanket over them or service them in the dark!

I feel like I have satisfied 690.14(C)(1) through(5) with my main DC disconnect down by the meter with the other disconnects, including the PV AC disconnect feeding the utility power. All disconnects are labeled, grouped, suitable for use, and installed in a readily accessible location. I am just adding one more on the roof. THOUGHTS!!??

P.S. All my work is here in Colorado, including FC.

Mike
 

George Stolz

Moderator
Staff member
If you can disconnect the conductors from your PV panels at grade level, and then they go elsewhere (into the building, inverter, whatever), then you can add switches on the roof until you can't lift your arms anymore, as I read this section.

Sounds like you've got it covered. :D

But unless some more people read this and chime in, then you're gonna have to go back and tell the inspector that some nutjob RW outside his scope of work was the only guy with an opinion. That wouldn't do. :)
 
georgestolz said:
If you can disconnect the conductors from your PV panels at grade level, and then they go elsewhere (into the building, inverter, whatever), then you can add switches on the roof until you can't lift your arms anymore, as I read this section.

Sounds like you've got it covered. :D

But unless some more people read this and chime in, then you're gonna have to go back and tell the inspector that some nutjob RW outside his scope of work was the only guy with an opinion. That wouldn't do. :)
For a nutjob RW, you should be taking your journryman's exam ASAP. Thanks for the help!
 

George Stolz

Moderator
Staff member
Hydro, click here for a related conversation we had on this a year ago.

Don't expect me to show up on the doorstep or anything, but whose jurisdiction you working in on this? The state?
 

peteo

Senior Member
Welcome. Sometimes I can't write anything after a George comment because I'm laughing too hard. :D :D

PV modules, their wiring, and those sections of the NEC I know nothing about. (Amazed to learn that shorting the DC terminals simply reduces current to zero, not exactly intutively obvious.) Found an article from someone who does, however. The references at the end of that article can take you further, if your questions are not addressed directly. The article is here.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
hydroelectric said:
Larry:

Got anything tangible on my question??
If the question in question is whether you can have a not-readily-accessible diconnect in line with a readily-accessible one, I'd say yes.
 
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