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#193720 - 04/15/10 12:04 PM Roof top disco for solar PV
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9012
Loc: Estero,Fl,usa
Currently the NEC does not require a roof top disconnect for solar panels. Should it?
There is a story out of California of a fire that could not be put out until someone with the proper PPE could cut the wires on the roof.
This does not seem to be addressed in the accepted changes to the 2011 either.
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#193843 - 04/22/10 08:18 PM Re: Roof top disco for solar PV [Re: gfretwell]
Yoopersup Offline
Member

Registered: 03/04/03
Posts: 826
Loc: Michigan
I really think thats not gonna work out on a 4/12 pitch house roof.

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#193849 - 04/23/10 01:34 AM Re: Roof top disco for solar PV [Re: Yoopersup]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9012
Loc: Estero,Fl,usa
Why not?
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#193853 - 04/23/10 10:55 AM Re: Roof top disco for solar PV [Re: gfretwell]
Yoopersup Offline
Member

Registered: 03/04/03
Posts: 826
Loc: Michigan
I suppose you could build a Unistrut rack up there or mount it on the side of the Chimmey, Then since its the ist disconnect should be readily accessable so put a latter going to it.
Most have conduit on outside of house down to an accesible one at ground level.
Sometimes common sense has to enter into the picture.

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#193854 - 04/23/10 11:13 AM Re: Roof top disco for solar PV [Re: Yoopersup]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9012
Loc: Estero,Fl,usa
Since these things are producing pretty modest power I would think a DC rated snap switch in a bell box would do the trick, particularly if you had one per array.
Maybe a contactor with a switch at ground level would work better tho.
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#193857 - 04/23/10 12:53 PM Re: Roof top disco for solar PV [Re: gfretwell]
HotLine1 Offline

Member

Registered: 04/03/02
Posts: 6785
Loc: Brick, NJ USA
I seem to have heard somewhere that turnout gear and a fire ax worked well.

Another was to cover the solar panels with a tarp!
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#193890 - 04/26/10 10:45 AM Re: Roof top disco for solar PV [Re: HotLine1]
harold endean Offline
Member

Registered: 02/16/02
Posts: 2248
Loc: Boonton, NJ
Greg,


I have read several stories about fireman getting zapped from a PV system while they are fighting a fire. I have also seen a new PV system where the converter is right on the roof. It sends down AC power and it has overcurrent protection. This way you can use regular NM wire in the walls which helps to protect the cable from sunlight and damage. Also it helps when you lose AC from the grid, the DC stops on the roof and doesn't continue down like the normal PV systems do.

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#193898 - 04/26/10 08:35 PM Re: Roof top disco for solar PV [Re: harold endean]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9012
Loc: Estero,Fl,usa
When you put the inverter on the roof you invoke 690.14(D)
Quote:

(D) Utility-Interactive Inverters Mounted in Not-Readily-Accessible Locations. Utility-interactive inverters shall be permitted to be mounted on roofs or other exterior areas that are not readily accessible. These installations shall comply with (1) through (4):
(1) A direct-current photovoltaic disconnecting means shall be mounted within sight of or in the inverter.
(2) An alternating-current disconnecting means shall be mounted within sight of or in the inverter.
The requirements in 690.14(D)(1) and (D)(2) provide for servicing disconnects at the inverter.
(3) The alternating-current output conductors from the inverter and an additional alternating-current disconnecting means for the inverter shall comply with 690.14(C)(1).
The disconnect required by 690.14(C)(1) allows the inverter(s) and the circuit to it (them) to be de-energized from a readily accessible location.
(4) A plaque shall be installed in accordance with 705.10.


italics indicates handbook commentary

The disconnect referenced in 690.14(C) is the building disconnect and follows the basic rules of a service disconnect. Obviously the folks who wrote this do not think the DC side is worth worrying about and they are not particularly interested in anything outside the building beyond the serviceability of the inverter.

I think that ignores the danger of high voltage, high current DC but nobody asked me. All I can say is be careful up there.
If nothing else, take off your jewelry wink
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#193901 - 04/27/10 01:58 AM Re: Roof top disco for solar PV [Re: gfretwell]
Wolfgang Offline
Member

Registered: 09/25/05
Posts: 154
Loc: the very West of Germany
Moeller Germany("an EATON brand" now) is just promoting a "firemen disconnect" for pv installations with DC capabilities up to 1kV in a variety of forms.

If actuated it shortens the dc part, so no dangerous voltage shall be present. I think they are not yet available in numbers but might be sold with you quickly if there is a real demand in the market.

Didn't find an English description. Maybe to be sold in the US not as "Moeller" but directly as "Eaton". Btw, also here the standards are behind reality.

Here a link to a German descrpition on www.moeller.net with some photos:
http://www.moeller.net/binary/presse/publications/de_special_09_09.pdf

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#193902 - 04/27/10 02:34 AM Re: Roof top disco for solar PV [Re: Wolfgang]
frenchelectrican Offline

Member

Registered: 02/06/03
Posts: 938
Loc: Wi/ Paris France { France for ...
Greg.,

IIRC the NEC code commite did talk about the PV DC disconnection but it seems they never get to the moot point for safety issue and what I am aware with roof top photocell array they should have DC disconnect switch and I did see at least two did not have proper disconnect switch on the roof top set up the other issue is voltage class that something I know it will cross the line here.

I am not suprised with solar panels can crank pretty serious voltage I know the last one I did couple quick repairs the DC solar panels there were running about 370 or so Volt DC so that one reason why I feel it allready cross the line for safety on resdential area.

Wolfgang I did see the link about the solar disconnect switch device that look good.

I will dig up and find our verison { France } and compared to the USA verison as well.

Merci,Marc
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