LOTO and integrated solar PV systems

[Jraef]

I had an interesting situation posed to me the other day in consulting for a Solar Array company. Someone is installing their solar PV array that is essentially roof tiles with PV cells integrated into them. The wiring is done via a track system that collects the power and penetrates the roof into the attic space in one place. The local Fire Marshal is insisting on a disconnect at the penetration so that his firefighters do not encounter live conductors after killing utility power when they arrive to fight a fire (a reasonable request).

So the installing contractor wants to remotely disconnect the power with a DC contactor mounted inside the attic directly under the penetration because the building owner does not want a big ugly disconnect on the roof or the side of the house. He is saying that he paid extra for the integrated system so that he wouldn't have that aesthetic issue.

I thought that there is another problem not mentioned: LOTO. Although that DC contactor's coil circuit can be locked out via a padlockable control switch, would that really qualify as a valid LOTO system? The issue I see potentially wrong with that is that it is not a positive air-gap system. The contactor could be welded and killing power to the coil would not disconnect the DC power coming from the PV array. I have seen something similar done for very large pump motors however, where installing a local 1200A disconnect switch next to the motor is considered impractical, but in those cases there was another remote disconnect in the switchgear room that could be locked out; it just was not within sight.

Problem is, I don't see this addressed anywhere. NFPA79 would be where I think it would be, but that is for machinery and operation, not electrical isolation of a power generating source. Is this a brave new world issue?

I would like opinions on this or if anyone has had a ruling and knows a code reference, even better.

 

[iwire]

They can not use a control circuit as a disconnecting means.

See NEC 2008 690.17 and 690.13.

 

[SegDog]

safety first

safety first

The very nature of the roof-integrated, attic intrusive set-up brings in a whole new set of concerns. Without knowing the details, having a readily accessible combiner/disconnect with proper signage is the goal.

In practical terms, when the fire truck pulls-up to the house, they need to see a junction box with a lockable switch that effectively isolates the PV strings. Because of the variety of designs, there's no "one size fits all".

Bringing the combiner-box down to ground level will make everyone happy, especially the inspector.

 

[Jraef]

The very nature of the roof-integrated, attic intrusive set-up brings in a whole new set of concerns. Without knowing the details, having a readily accessible combiner/disconnect with proper signage is the goal.

In practical terms, when the fire truck pulls-up to the house, they need to see a junction box with a lockable switch that effectively isolates the PV strings. Because of the variety of designs, there's no "one size fits all".

Bringing the combiner-box down to ground level will make everyone happy, especially the inspector.

No, that's what they have been doing and although the Electrical Inspector is satisfied, the Fire Marshal is insisting on having no conduit runs with live conductors, with the exception of the short piece going into the attic. This is apparently spreading among Fire Marshals as well, they got a third inquiry yesterday.

But it looks as though the LOTO issue is moot, the control circuit lockout will not satisfy it. They were hoping to be able to eliminate the disconnect at the combiner box, but they will not (which is what I told them). So that DC contactor will only be there to satisfy the Fire Marshal, everything else still needs to be there.

 

[SegDog]

combiner box on roof or not...???

combiner box on roof or not...???

I'm not sure about "that's what they have been doing", since the combining of serial strings into parallel is where the danger is. Bringing the serial conductors down to the ground is what I am suggesting. There are certainly other ways. Without sunlight, it is moot.