Friends:
One of my favorite things about this list-service: The minute I think I have posted something really stupid, someone agrees with me. What a self-esteem builder! Thanks, Bradley! Here are two conclusions I think I am arriving at with this discussion: 1. The language in the 2017 NEC is pretty vague on the issue. Hopefully this improves over time. 2. The point is really open to interpretation. If you can convince your building department that RSS is not required on a ground mount array, I think it is entirely safe to omit the RSS. This is a reasonable case to make if one goes on the assumption the intent is to protect firefighters on roofs. Thanks for the lively discussion. The points we are all thoughtfully presented. William Miller Solar 17395 Oak Road, Atascadero, CA 93422 805-438-5600 www.millersolar.com CA Lic. 773985 *From:* Bradley Bassett [mailto:bbasse...@gmail.com] *Sent:* Tuesday, February 1, 2022 2:15 PM *To:* RE-wrenches *Cc:* William Miller *Subject:* Re: [RE-wrenches] Rapid Shutdown for Off-grid systems "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 On Tue, Feb 1, 2022 at 11:23 AM Brian Mehalic <br...@solarenergy.org> wrote: Sorry, forgot to state my previous comment was in regards to a ground-mount. Brian On Feb 1, 2022, at 12:19 PM, William Miller <will...@millersolar.com> wrote: 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 CA Lic. 773985 *From:* RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *Ray *Sent:* Tuesday, February 1, 2022 10:11 AM *To:* re-wrenches@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: Jay: Here is the text from 2017: *690.12 Rapid Shutdown of PV Systems on Buildings. PV* *system circuits installed on or in buildings shall include a rapid* *shutdown function to reduce shock hazard for emergency* *responders in accordance with 690.12(A) through (D).* *Exception: Ground mounted PV system circuits that enter buildings, of* *which the sole purpose is to house PV system equipment, shall not be* *required to comply with 690.12.* The wording is interesting. The requirement is directed at “PV system circuits…”, not PV arrays. The passage does not specify where the PV feeding those circuits is located, it just addresses where the circuits are, specifically “in or on a building.” The only circuits that are exempt are those feeding a building that serves only one purpose, to house PV equipment. For circuits that enter building with other uses—homes, garages, barns, workshops, etc.-- it would seem there is a requirement to have rapid shutdown systems (RSS). Reading through the rest of the section, I don’t see any language that gets us out of the requirement to reduce voltages to less than 80 volts within 30 seconds inside the array boundary, as in module level shutdown, regardless of roof-top or ground-mount. Although the 2020 code includes some differing language, I don’t see it as exempting ground mount systems. The moral of the story is this: For ground-mounts: either install RSS or put your equipment (inverters, charge controllers, batteries, BOS) in a separate building housing only that equipment. I don’t necessarily like the requirement, but I think it exists. Jay, or anyone, please, please tell me I am reading this incorrectly. By the way, regarding battery circuits, here is a quote from a post by Bill Brooks on March 16, 2016: *In the 2017 NEC, we were very careful to carve out all batteries and loads,* *that were previously part of PV systems, and place them in their own* *articles.* I have not read through the battery sections of the code to verify this, I am taking Bill at his word. William Miller Miller Solar 17395 Oak Road, Atascadero, CA 93422 805-438-5600 www.millersolar.com CA Lic. 773985 *From:* Jay [mailto:jay.pe...@gmail.com] *Sent:* Tuesday, February 1, 2022 6:07 AM *To:* will...@millersolar.com; RE-wrenches *Subject:* Re: [RE-wrenches] Rapid Shutdown for Off-grid systems 2017 code has a specific exception/clarification for ground mount solar that it does not need RS. It’s in the first line after 690.12 Jay On Feb 1, 2022, at 12:13 AM, William Miller <will...@millersolar.com> wrote: Jerry: Yes it is required. Rapid Shutdown: NEC 690.12. All buildings except dedicated solar buildings. Read it and weep. William Miller Solar 17395 Oak Road, Atascadero, CA 93422 805-438-5600 www.millersolar.com CA Lic. 773985 *From:* Jerry Shafer [mailto:jerrysgarag...@gmail.com] *Sent:* Monday, January 31, 2022 7:21 PM *To:* William Miller; RE-wrenches *Subject:* Re: [RE-wrenches] Rapid Shutdown for Off-grid systems William Are you sure RSD is required on a non habitable building, historically its not required. Now that being said we use fire raptor with the best results, yes it takes an extra conduite and might require a button and power supply depending on inverter application. Jerry On Mon, Jan 31, 2022, 9:57 AM William Miller <will...@millersolar.com> wrote: Friends: It is quite rare for us to install off-grid systems on roof-tops. We have one coming up with about 20kW on a large barn roof. This will be our first off-grid with a module-level rapid shutdown requirement. I see no exemptions from RSS for off-grid systems in the code. I have looked at the options and this is what I have found: 1. Fire Raptor 2. Tigo TS4-F 3. AC coupling with micro-inverters or optimizers No one of these approaches seems ideal. The fire raptor requires extra wiring for control leads. The Tigo requires a wireless control system which worries me about reliability. With AC Coupling systems floating the proposed AGM batteries may be awkward. Furthermore, with AC coupled systems one cannot charge batteries unless the mini-grid is operational, a big problem. Have any of you implemented module-level RSS on a battery-based inverter system? I looked in the archives and found no threads that apply. Thank in advance. William Miller _______________________________________________ List sponsored by Redwood Alliance Pay optional member dues here: http://re-wrenches.org List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org There are two list archives for searching. 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