PV disconnect questions

[hubbs1982]

Good evening!

I am planning out my solar system for a new construction house. It will be roof mounted with 3 strings of 11 Longi 355W panels feeding a EG4 18kpv.

I had my electrician run 1-1/4” PVC conduit in the attic from 3 different roof locations that terminate in the garage. Before we insulate an Sheetrock, I want to locate the PV disconnect.

My current thoughts are to use a 6”x6”x4” junction box in the wall and have the conduit terminate in the box. I will then mount a PV disconnect on the exterior wall butted up to the junction box - does this sound feasible?

For the disconnect, I am looking at this unit from IMO https://imoautomation.com/imo_us_usd_view/enclosed-dc-switch-ip66-6249fb33691e8.html or this from Siemens https://mall.industry.siemens.com/mall/EN/US/Catalog/Product/?mlfb=US2:HNF361RPV

These seem roughly the same price, is one better than the other?

Does this from MidNite https://www.solar-electric.com/mnde...Wp4f5piR34ahvNgnTC0wf2FqhAOLlB7gaApwvEALw_wcB provide any additional benefit?

Also, I am using Tigo optimizers with the CCA, how does it integrate with disconnect?

Lastly, what is the best way to incorporate RSD?

Many thanks!

 

[zanydroid]

For the disconnect, I am looking at this unit from IMO https://imoautomation.com/imo_us_usd_view/enclosed-dc-switch-ip66-6249fb33691e8.html or this from Siemens https://mall.industry.siemens.com/mall/EN/US/Catalog/Product/?mlfb=US2:HNF361RPV

These are quite apples to oranges. Why did you put the Siemens in the same story? I believe that one can only disconnect one string. You have to disconnect + and - for ungrounded solar. Everything residential is ungrounded these days and you can confirm in your inverter manual that the strings must be ungrounded. And I mean the frames are grounded but neither + nor - CCC are grounded. That Siemens disconnects 3 wires. With ungrounded solar you can successfully use 2 of those leaving the third impotent. With the almost never seen in residential grounded solar you can indeed use this.

RSD is somewhat independent of disconnect. The canonical way is to connect shutdown of inverter to the keep alive signal. By tying the power supply of CCA to an inverter AC or DC output. I say somewhat independent bc throwing the disconnect will also trigger RSD on some RSD systems based on PLC. But it will not do this on the CCA! Because the CCA is a wireless signaling system. Sure you have to wire CCA up to the roof but this is just the wired backhaul.

So in your hardware choice disconnect is rather independent of RSD

(You seem to have asked the same RSD question in two ways)

 

[wpns]

Well, first, check with your AHJ for their requirements, if (for instance) they require metallic conduit you need to know that before you start closing up.

Second, check with your AHJ for RSD requirements, most places now require it for solar panels on roofs. I'd recommend RSD even if they don't require it, it's _much_ safer for you to work on and the RSD switch can be https://www.amazon.com/gp/product/B0BL34P2NT which shuts down my panels, inverters, and batteries from a single location.

Not sure I'd bother with the optimizers, it's not clear how much if any benefit they add, at the expense of significantly more complexity. just put a Tigo RSD box on each panel and you're done.

 

[zanydroid]

Oof I missed that PVC in attic thing. That is likely a must-redo

 

[hubbs1982]

These are quite apples to oranges. Why did you put the Siemens in the same story? I believe that one can only disconnect one string. You have to disconnect + and - for ungrounded solar. Everything residential is ungrounded these days and you can confirm in your inverter manual that the strings must be ungrounded. And I mean the frames are grounded but neither + nor - CCC are grounded. That Siemens disconnects 3 wires. With ungrounded solar you can successfully use 2 of those leaving the third impotent. With the almost never seen in residential grounded solar you can indeed use this.

RSD is somewhat independent of disconnect. The canonical way is to connect shutdown of inverter to the keep alive signal. By tying the power supply of CCA to an inverter AC or DC output. I say somewhat independent bc throwing the disconnect will also trigger RSD on some RSD systems based on PLC. But it will not do this on the CCA! Because the CCA is a wireless signaling system. Sure you have to wire CCA up to the roof but this is just the wired backhaul.

So in your hardware choice disconnect is rather independent of RSD

(You seem to have asked the same RSD question in two ways)

I was looking at the Siemens as I thought it could handle 3 strings. I guess I was mistaken.

Looks like I have some more reading to do.

 

[hubbs1982]

Oof I missed that PVC in attic thing. That is likely a must-redo

I spoke with the chief electrical inspector for the AHJ who told me PVC is fine in the attic/walls as long as it is not plenum space.

 

[zanydroid]

I spoke with the chief electrical inspector for the AHJ who told me PVC is fine in the attic/walls as long as it is not plenum space.

Did you get that in writing or verify that you have a local amendment? BC I thought Article 690 was pretty specific about this

There could also be a misunderstanding on their part of the project or of code. Since this 690 is PV specific. And this metallic conduit rule within 690 is even more specific — DC PV circuits

EDIT: so I would say there is some risk here even with written dispensation unless the writing is very specific