Hi William, Yes, the bulletin I attached was just an example of a 100% rated disconnect (which happened to be DC since that's the one I had handy!). My understanding is that most of the NON-fused Square D switches are rated for 100%.
See this FAQ from the manufacturer: https://www.schneider-electric.us/en/faqs/FA237949/, quoted below: > *Resolution:*All General Duty, Heavy Duty or Double Throw Safety Switches > maximum current rating, either 80% or 100% of the nameplate rating, depends > on if the switch is Fusible or NON-Fusible. > > - Fusible switches are rated to carry up to 80% of the amp rating of > the fuses installed in the switch > > > - Non-fusible (unfused) switches are rated to carry 100% of the switch > nameplate ampere rating > > Regarding this point: > If, hypothetically, you could find a 30A disconnect that was continuous > duty rated, if it is fed by a 40 Amp breaker, as I believe would be > required, then the 30 Amp disconnect is still not suitable. You can not > feed a 30 Amp rated device with more than 30 Amps. I believe the original poster was asking about a 6000W inverter with 25A max output. So in that case you could use a 100% rated non-fusible disconnect, because the max current is only 25A. (The required 40A breaker is sized larger because commonly available breakers are only 80% rated, not 100%. But the max current is still only 25A.) See 690.8(A) for calculation of maximum circuit current, specifically section (3) for inverters: "The maximum current shall be the inverter continuous output current rating." (Not "the inverter continuous output current multiplied by 1.25.") Best, Blake On Wed, Aug 21, 2019 at 10:59 PM William Miller <will...@millersolar.com> wrote: > Blake: > > > > Thanks for sharing the data sheet. The document applies to DC PV systems, > however, and I believe the discussion pertains to the AC inverter output. > Therefore the bulletin you attached does not apply here. > > > > (Note also that this data sheet indicates you need to use two poles for > any application, ungrounded or grounded. I believe that requirement was > usurped later on for Square D Heavy Duty switches, but again, that is for a > different application.) > > > > I looked again at Square D general and heavy duty safety switches rated at > 30 Amps and I could not find any reference that these switches are > continuous duty rated. I still believe that for the application described, > the 125% rating has to be applied. > > > > If, hypothetically, you could find a 30A disconnect that was continuous > duty rated, if it is fed by a 40 Amp breaker, as I believe would be > required, then the 30 Amp disconnect is still not suitable. You can not > feed a 30 Amp rated device with more than 30 Amps. > > > > Bottom line, a 30 Amp disconnect will not meet code on the described > project. > > > > William Miller > > > > > > > > Miller Solar > > 17395 Oak Road, Atascadero, CA 93422 > > 805-438-5600 > > www.millersolar.com > > CA Lic. 773985 > > > > Quote of the month: “As they age, batteries transition from energy > > storage devices to energy consuming devices.“ W. Miller > > > > *From:* RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org] *On > Behalf Of *Blake Gleason > *Sent:* Wednesday, August 21, 2019 4:20 PM > *To:* RE-wrenches > *Subject:* Re: [RE-wrenches] 30 amp disconnect/40 amp breaker > > > > Typically a fused disconnect can only handle 80% of it's nominal current > on a continuous basis. Unfused disconnects are often 100% rated. For > example, see attached Square D bulletin #3110DB0401R0410. > > > > So, a 100% rated (unfused) 30A disconnect (at least, from Square D) should > be fine here, as long as your OCPD is provided elsewhere (eg, the breaker > you mentioned). > > > > NEC 690.8(B)(1)(Exception) explicitly allows a 100%-rated device to be > used without multiplying the inverter output current by 125%. > > > > > > On Wed, Aug 21, 2019 at 3:22 PM Greg <g...@remotepowerinc.com> wrote: > > Fellow Wrenches, I'm having a discussion with a utility engineer > regarding the following situation: > > Installing a 6kW inverter that has a full rated output of 25 amps. 80% of > 30 is 24. That means to me I need to go up to a 40 amp breaker. I'm > running #8 (continuous load 25 x 1.25 etc.) > The engineer believes I should use a 60 amp disco since it's on a 40 amp > breaker. My thinking is I can use a 30 amp disco since it can not produce > more than 25 amps ever. > > Do any of you have a reference that shows what I'm doing is okay? Not > okay? > > Thanks again, > Greg Egan > Remote Power Inc. > > _______________________________________________ > List sponsored by Redwood Alliance > > 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 > > List-Archive: > http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > www.members.re-wrenches.org > > > > > -- > > > > > > *Blake Gleason, PE* | Employee-Owner | > > *Director of Innovation & Technical Excellence* > > > 510.845.2997 x128 > > Follow us on Facebook > <https://www.facebook.com/pages/Sun-Light-Power/119675658118322?ref=hl>, > LinkedIn <https://www.linkedin.com/company/sun-light-and-power> or our > website <https://sunlightandpower.com/>. > > > _______________________________________________ > List sponsored by Redwood Alliance > > 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 > > List-Archive: > http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > www.members.re-wrenches.org > > -- *Blake Gleason, PE* | Employee-Owner | *Director of Innovation & Technical Excellence* 510.845.2997 x128 Follow us on Facebook <https://www.facebook.com/pages/Sun-Light-Power/119675658118322?ref=hl>, LinkedIn <https://www.linkedin.com/company/sun-light-and-power> or our website <https://sunlightandpower.com/>.
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