[RE-wrenches] Rapid Shutdown for Off-grid systems

Wed Feb 2 10:55:47 EST 2022

Hey Brad and All,

We've been switching (pun intended:)) from SQ D HU361s to IMO DC 
Isolators <https://www.imopc.com/products/10000000>
with good results.  They make 2,3,4,5,6,8 pole units and that lends 
itself well to actually switching both poles at reasonable cost.

As for the RSS discussion. I'm hearing some others imply that if "any" 
DC circuits from a ground mount are on or in a building that the whole 
array needs RSS?  I don't believe that's what the code intends at all 
and is certainly uncalled for from any safety standpoint.

We've had many inspectors okay a simple PV Disconnect on the DC side of 
a ground mount - either on the house or even at the array - as the RSS 
for DC lines if they do then enter a building - so simply putting an RSS 
sticker on the DC PV disconnect before it enters the building - end of 
story.  That's our common practice on ground mounts.

Hope that helps!

Best,

Jeff

> Bradley Bassett <mailto:bbassett2 at gmail.com>
> February 1, 2022 at 2:14 PM
> "A switch, outside of the building, opening the PV circuit to the 
> power electronics, and functioning as the pv system disco and the 
> rapid shutdown initiation device, should be all that is required."
>
> That is what I have found most inspectors will accept, but not all. A 
> strict reading of the code does come to the same conclusion that 
> William comes to, and some inspectors will require that. The code is 
> not very specific on where the PV system disconnect should go. It 
> seems to be mostly accepted to be on the PV side of the charge 
> control, but when I read the code strictly it seems to me it should be 
> on the battery side of the charge control since it is only a PV 
> device. Fortunately the PV side is more accepted because that makes 
> things much easier.
>
> What I'm still having trouble with is the requirement for 
> breaking both pos and neg legs in the PV system disconnect unless 
> solidly grounded which most systems are not (690.13(E)). I see that 
> most installers do not break both poles, but only the positive leg, 
> which is of course easier and less expensive. I've quoted the use of 
> dual pole breakers when possible, but OutBack does not really call for 
> that always, and if you ask about their 2 pole 300V breakers they (and 
> Carling) don't say they can be used that way. And if you do, you 
> have to run the wires in opposite directions for polarity. I've asked 
> for clarification but have not received it yet. Then there are the 
> high voltage charge controls like Schneider, where often one uses the 
> SqD HU361, which can be wired in various ways to meet the 600V 
> requirement. It can be wired one pole for up to 18A Isc for PV, or up 
> to 30A if two poles in series, or one pos and one neg pole in the 
> circuit. The Schneider RS Disco does break both poles, one of the few 
> devices that make it clear. I'm curious what others are doing.
>
> Brad
>
>
>
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> Brian Mehalic <mailto:brian at solarenergy.org>
> February 1, 2022 at 11:23 AM
> Sorry, forgot to state my previous comment was in regards to a 
> ground-mount.
>
> Brian
>
>
>
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> William Miller <mailto:william at millersolar.com>
> February 1, 2022 at 10:24 AM
>
> Ray:
>
> Thanks for that input.  I was hoping I was wrong.  I looked for that 
> discussion in the archives but could not find it.
>
> William
>
> Miller Solar
>
> 17395 Oak Road, Atascadero, CA 93422
>
> 805-438-5600
>
> www.millersolar.com <http://www.millersolar.com/>
>
> CA Lic. 773985
>
> *From:*RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org 
> <mailto:re-wrenches-bounces at lists.re-wrenches.org>] *On Behalf Of *Ray
> *Sent:* Tuesday, February 1, 2022 10:11 AM
> *To:* re-wrenches at lists.re-wrenches.org 
> <mailto:re-wrenches at lists.re-wrenches.org>
> *Subject:* Re: [RE-wrenches] Rapid Shutdown for Off-grid systems
>
>  Ground mounts do NOT require RSS.  We hashed this out years ago on 
> the Wrenches list, when NEC 2017 came out.
>
> See Figure 690.1(B) Note (2): /" The PV system disconnect in these 
> diagrams separates the PV system from all other systems"./
>
> Thus, the PV disconnect is defined as the transition point from the PV 
> system to all other systems, like battery or inverter systems. The 
> installer/ designer decides where to put that disconnect.  I usually 
> put it on the wall before it goes into the building, and I have never 
> had an inspector question that.
>
> Thanks,
>
> Ray Walters
> Remote Solar
> 303 505-8760
>
> On 2/1/22 10:06 AM, William Miller wrote:
>
>
>
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