DC Disconnect with 6 poles ( for lack of better term)
- Thread starter aelectricalman
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ControlFreak
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- Location
- Asheville, NC
http://www.cooperbussmann.com/pdf/403fe732-43a6-4835-ba55-fd51dc53f45b.pdf
Here you go. See page 77, maybe?
aelectricalman
Senior Member
- Location
- KY
Thats how it was specd. I hate it.
- Location
- Connecticut
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- Engineer
Not rated for DC. It doesn't appear any of their 6 pole switches are DC rated.
- Location
- Massachusetts
In that case it seems that part of the 'specifiers' job would be to specify the switch.
Perfect time to use an official RFI.
Can't blame you at all, it does sound stupid.
dbuckley
Senior Member
- Location
- Canterbury, New Zealand
Oops, you'd still need two switches for the six inverters. My bad.
How could we possibly know this from the info given?
We can't.
Depending on the load a rotary disconect switch may be what you need.
Bob, when you work on your truck do you disconnect BOTH cables from the battery?
Unless the inverters are connected to the DC side in some sort of series arrangement, interrupting one lead from the DC will adequately disconnect them from the PV panels.
And for single phase circuits, do you open the neutral to work on it? Same principle IMHO.
I do agree that full info wasn't given , but c'mon this is not rocket science. :grin:
Not sure if it's legal but don't see why you would need to.
I do, but again, why bother?
Are ANY of the positives or negatives tied together? If not, then opening one leg for each array will safely disconnect the arrays.
Not impossible, use a pair of 3-pole switches with a mechanical linkage and you've got all six arrays with one handle pull.
But even with only two switches to be pulled it would still meet NEC disconnect requirements as it is far less that the six throws of the hand rule.
And as eprice pointed out, can the inspector produce a written reference for his requirement? If not, tell him politely where to stuff it. No inspector is allowed to make things up just because that's what he personally wants. If that was the case I would ban MWBC's. :grin:
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RETRAINDAILY
Senior Member
- Location
- PHX, arizona
Not a bad idea, but why over-engineer this thing?
And I believe the OP mentioned it cannot rely on contactors of any kind.
Two 3-pole disconnects with a simple mechanical linkage is simple, cheap, reliable and will do the job.
BillK-AZ
Senior Member
- Location
- Mesa Arizona
DC Disconnect with 6 poles
DC Disconnect with 6 poles
I did not see how many PV modules are involved.
An alternative is to use micro inverters such as Enphase (www.enphaseenergy.com). The output is 240 VAC, 1A per module, limit of 15 inverters per string. Really no need for a roof disconnect, if the AC line to the inverters is switched off, there is no voltage in the AC wiring and only the open circuit voltage of a single module is possible on the roof. Cost on a $/watt basis is only slightly higher than central high DC voltage inverters that you are considering, and lower in a $/watt if you have to use a larger than needed inverter because of size steps (i.e. need a 3000-watt inverter for 2900 watts).
The one PV module string per pole of a safety switch discussed by others is no longer UL listed by Square-D, only "Self-Certified by Schneider Electric". Eaton claims to be developing a Listed 3-pole switch, but it is not yet available.
DC Disconnect with 6 poles
I did not see how many PV modules are involved.
An alternative is to use micro inverters such as Enphase (www.enphaseenergy.com). The output is 240 VAC, 1A per module, limit of 15 inverters per string. Really no need for a roof disconnect, if the AC line to the inverters is switched off, there is no voltage in the AC wiring and only the open circuit voltage of a single module is possible on the roof. Cost on a $/watt basis is only slightly higher than central high DC voltage inverters that you are considering, and lower in a $/watt if you have to use a larger than needed inverter because of size steps (i.e. need a 3000-watt inverter for 2900 watts).
The one PV module string per pole of a safety switch discussed by others is no longer UL listed by Square-D, only "Self-Certified by Schneider Electric". Eaton claims to be developing a Listed 3-pole switch, but it is not yet available.
I are an engineer. I love over-engineering :grin:
12 total poles are required. 2-poles per circuit x 6 circuits. OP stated both legs of the DC had to be cut. I think pulling 12 mechanical legs might be a burden to pull with a single throw.
Frankly this is kind of an expensive proposition when having multiple 2-pole disconnects mounted side-by-side would work fine for the fire fighter. I mean really. Is it that tough for him to pull six levers like that? Who really came up with this requirement?
Could you explain this restriction?
LOL so that explains it.
Where did you see that? Nowhere did the OP state that both legs need to be cut. Again I ask do you pull BOTH cables off your battery when working on your vehicle? :grin: Unless the PV arrays feed the six inverters in some sort of series arrangement disconnecting one leg of the DC WILL cut the power completely.
The OP said the inspector is requiring it. Like I said before, the OP needs to tell the inspector to back it up with a Code or Local Ordinance reference (IN WRITING) or be told to stuff it.
And I totally agree that six standard disconnects mounted side by each would be fully Code Compliant in any event.
Presumably, the bold section says 6x2.
And I agree with you here, hence I asked for a better explanation. Is this just wishful designing on the inspector's part or is there some bizarre local code?
I can't help but think this inspector does residential homes and is looking for the equivalent of a single main breaker for a house.
6-pole DC Disconnect??
6-pole DC Disconnect??
Hi,
I might be late on this discussion but I just want to try to leave this issue clear. When more than two strings are to be connected to one inverter, each string has to go thru an overcurrent protection device, like a fuse. For that you willl need a combienr box with fused inputs and the output from that combiner box is what you will bring to the DC disconect (and interrupt only the unrounded wire).
So, in this case, depending on how many inverters will be handling the 6 strings, you will need to combine all the strings that will go to each inverter into a combiner (if more than 2 or into a splicing box if the total of strigns is equal or less than 2)
If you still wondering about the solution let me know.
6-pole DC Disconnect??
Hi,
I might be late on this discussion but I just want to try to leave this issue clear. When more than two strings are to be connected to one inverter, each string has to go thru an overcurrent protection device, like a fuse. For that you willl need a combienr box with fused inputs and the output from that combiner box is what you will bring to the DC disconect (and interrupt only the unrounded wire).
So, in this case, depending on how many inverters will be handling the 6 strings, you will need to combine all the strings that will go to each inverter into a combiner (if more than 2 or into a splicing box if the total of strigns is equal or less than 2)
If you still wondering about the solution let me know.
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