Request from local FD to be able to disconnect DC power produce by Array.

[remillard]

Since I teach PV courses in the area several local FD requested how the DC power produce by the Array can be disconnected when an alarm condition or Fire in the building?
I came up with two options 1) install a DC rated relay w/ proper ampere rating for the system on the roof next to the array and either control it with a shunt trip button next to FA panel or 2) feed the coil of the relay through a aux. contact in FA panel which would deenergize the coil of the relay when the FA panel is in ALARM condition.

Any other suggestions short of covering the array with fire rated blankets?

 

[jaggedben]

Several jurisdictions in our area require a manual DC disconnect on the roof next to the array. That's kind of halfway to what you're talking about, while less expensive and time-consuming to install.

Integrating things into the fire alarm system, if there is one, is not a bad idea.

I hope it's not too hard to find 600V DC rated outdoor relays.

 

[petersonra]

Several jurisdictions in our area require a manual DC disconnect on the roof next to the array. That's kind of halfway to what you're talking about, while less expensive and time-consuming to install.

Integrating things into the fire alarm system, if there is one, is not a bad idea.

I hope it's not too hard to find 600V DC rated outdoor relays.

I have used Siemens 3TC contactors with good service. You would need a box to put them in though. They are not cheap though. I think the 32A ones were almost $200 each.

I have also used a Siemens contactor that is part of their locomotive group that is good up to 2000A IIRC. Took a while for them to get here from Germany though.

 

[ron]

A big blanket over the arrays.

 

[Jraef]

I have used Siemens 3TC contactors with good service. You would need a box to put them in though. They are not cheap though. I think the 32A ones were almost $200 each.

I have also used a Siemens contactor that is part of their locomotive group that is good up to 2000A IIRC. Took a while for them to get here from Germany though.

Yes, there are only a few contactors available that are UL listed for use at 600VDC, the Siemens 3TC is one of them. I used to build them into remote disconnect panels for SunPower as a product they offered with their roof tile systems, because nobody wanted to spend the extra money for the roof tiles and then have a big old ugly disconnect on the roof. What they do is power the coil for the contactor from the utility supply so when the firefighters arrive and kill the utility source, it drops out all the contactors.

ABB has a 600VDC contactor too, I don't remember the series but you have to be careful, some ABB distributors are less than knowledgeable and will pick out the AC only device.

 

[BillK-AZ]

The UL Listing for Siemens 3TC contactors is:
----
PRODUCT COVERED:
USL, CNL - Magnetic Motor Controllers, Type 3TC44 followed by -1,
followed by ?3, -4, -5, -6, -7, -8 or -9 followed by 0A, 4A, 0B, 0C, 0H, 5K,
6M, 7M, 0L or 1L may be followed by suffix letters and/or numbers.
GENERAL:
These devices are open type 2-pole contacts intended to connect dc
motors directly across-the-line. They are provided with an ac or dc coil and
are provided with auxiliary contacts as mentioned in the Nomenclature
Breakdown
----
USL ? Indicates investigated to UL 508, 17th Edition
----

Is there any problem in having AHJs accepting these for PV use as a field installed component?

 

[Jraef]

The UL Listing for Siemens 3TC contactors is:
----
PRODUCT COVERED:
USL, CNL - Magnetic Motor Controllers, Type 3TC44 followed by -1,
followed by ?3, -4, -5, -6, -7, -8 or -9 followed by 0A, 4A, 0B, 0C, 0H, 5K,
6M, 7M, 0L or 1L may be followed by suffix letters and/or numbers.
GENERAL:
These devices are open type 2-pole contacts intended to connect dc
motors directly across-the-line. They are provided with an ac or dc coil and
are provided with auxiliary contacts as mentioned in the Nomenclature
Breakdown
----
USL ? Indicates investigated to UL 508, 17th Edition
----

Is there any problem in having AHJs accepting these for PV use as a field installed component?

They have been doing so for SunPower (the largest solar power supplier in the US) for about 3 years now. Mind you, these contactors are open type and Siemens doesn't offer them in a listed enclosed version, so we had them built into a small Hoffman enclosure with control terminals, which was given an overall UL508A label by a panel builder (my company at the time developed it for them then when the volume increased they took the production to Malaysia or China or somewhere like that, as is per usual in the Solar industry now).

By the way, you might be able to buy that assembly from a cooperative SunPower dealer, if they know who to ask for it from. If you are not using a SunPower array, you might have to "conceal the truth" a bit to get them to cooperate. <nudge nudge wink wink> If not, and you need more than one, you could go to a UL508 shop to have it built and labeled.

 

[petersonra]

If not, and you need more than one, you could go to a UL508 shop to have it built and labeled.

I am sure the company I work for would be quite happy to make you as many as you wanted with a nice UL 508 label on them.

We would probably even give you a quantity discount if you wanted to buy 1000 of them.

 

[BillK-AZ]

Therefore the installed item as far as the AHJ is concerned is a UL508 Labeled item, not a Listed contactor.

 

[petersonra]

Therefore the installed item as far as the AHJ is concerned is a UL508 Labeled item, not a Listed contactor.

My personal opinion is it would be better to just put the contactor in a box yourself. As long as you are not assembling a bunch of other compoenents into the box it probably serves no real purpose to list it as an assembly.

 

[Marvin_Hamon]

Unfortunately there are few real options. All the disconnect options most people will talk about only disconnect the PV strings from the rest of the system. The strings are still energized to whatever the string voltage is, up to 600V in most systems, and this is not what the FD really wants when it asks for a way to turn off the array. They want all of the conductors in the system to be de-energized and the only way to come close to doing that is to disconnect the modules at the module junction box. The only reasonable way to do that is to have some control built into the junction box, like a DC/DC converter or a microinverter, that can be controlled from a central location. Even this will leave the individual modules energized if exposed to the sun so the only 100% sure way to remove all voltage potential is to blanket the modules.

 

[ggunn]

Unfortunately there are few real options. All the disconnect options most people will talk about only disconnect the PV strings from the rest of the system. The strings are still energized to whatever the string voltage is, up to 600V in most systems, and this is not what the FD really wants when it asks for a way to turn off the array. They want all of the conductors in the system to be de-energized and the only way to come close to doing that is to disconnect the modules at the module junction box. The only reasonable way to do that is to have some control built into the junction box, like a DC/DC converter or a microinverter, that can be controlled from a central location. Even this will leave the individual modules energized if exposed to the sun so the only 100% sure way to remove all voltage potential is to blanket the modules.

Well, there are combiner boxes with integrated discos. The home runs to the combiners will still be hot, though.

 

[jaggedben]

My impression is that we are talking about adding an additional relay disconnect box somewhere under or very close to the array, such as right next to the combiner.

I think it's basically a good idea, especially on large systems or large buildings where there is already a fire alarm system. When there are long DC conduit runs from array(s) to inverter(s), it makes sense to be able to separate the two in a fire. If the fire just happens to be caused by a fault in the DC conduit somewhere after the relay disconnect, tripping the relay could actually kill the source of the fire and it may burn itself out. If it doesn't burn itself out, firefighters can put it out without it reigniting itself. If the fire isn't caused by the solar system, then tripping the relay prevents the DC wires in the conduit becoming a second source of fire if the conduit is damaged by the fire remotely from the array. It doesn't kill the PV power as completely as blankets, but as a safety measure, it kicks in much, much more quickly and without relying on human comprehension of the situation.

If the fire is in the array itself, that's a whole different ballgame anyway.

I think there is going to be plenty of wishing for additional training of firefighters, both regarding how to fight a fire in the array itself, and how to recognize a fire caused by PV output circuits in a location remote from the array.

 

[Marvin_Hamon]

I have seen systems integrated into fire annunciation panels that control contactors in the PV source circuit combiner boxes. Several DC combiner box manufacturers make combiners with contactors and since they are controlled remotely it is easy to set up a big red button somewhere, or have them automatically operate on loss of AC service, or controlled by the fire panel. They are quite expensive through which leads folks to try to make up their own remote disconnects.

While these will disconnect the DC runs from the combiners to the inverters I still think the ultimate answer is to put the disconnect in each module's junction box. We have the technology today but it adds maybe $30 to the cost of a module and unfortunately increased safety does not always lead to sales when the system price is significantly higher. This is something that will have to be addressed in the code just like arc fault is. Do not be surprised if a future NEC requires module level disconnects on building mounted PV systems. When that is in the code then systems will be built to use it, and since everyone will have to use it the price difference will come down.

That's my take anyway.