In 2008, we have had to replace our standard Sq. D HU361RB used since our beginnings, with the Sq. D H361RB (U stands for unfused). Was there some sort of code change NEC or CBC maybe that made most jurisdictions in So Cal suddenly start requiring fused DC disconnects? Typically, we fill the fused Sq. D. box with 15A 5" fuses. Peter D.
_____ From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of William Miller Sent: Friday, November 21, 2008 9:43 AM To: RE-wrenches Subject: Re: [RE-wrenches] DC Rating of Disconnects Peter: I am resending, the first version inexplicably deleted some text: An arc is created in the process of disconnecting any current under load. DC circuits have an enhanced ability to sustain that arc. PV circuits exacerbate this problem as a short or load is disconnected because they can sustain a short but the voltage rises drastically as a circuit is disconnected. This all justifies the added expense of a DC rated disconnect. We use the Square D HU361 without hesitation. There are few alternatives available and none with any significant cost savings. In selecting a disconnect, a design-build contractor must use the highest Voc possible. Make sure you are entering the 690.7 table with the record low temperature for the location. If we used a disconnect without the correct rating we would open ourselves to unacceptable liability exposure and, worse yet, would not experience that pleasant feeling one gets when you know you've done the job right. William Miller At 09:11 AM 11/21/2008, you wrote: _____ From: Peter Parrish [mailto:[EMAIL PROTECTED] Sent: Friday, November 21, 2008 9:10 AM To: 'RE-wrenches' Cc: 'Peter Parrish' Subject: DC Rating of Disconnects I am looking into using the PV Powered PVP2000 inverter for some small, low voltage designs. The string Voc will be around 200 Vdc, worst case. Since the PVP2000 doesnt come with a DC disconnect, I am wondered what other wrenches who install the PVP2000 have been doing about this. I hate to spend $150 on a 600 V AC/DC disco such as the SD HU361RB to provide the means of disconnection. I believe that the 240 V AC discos such as the SD DU221RB have no DC rating. >From an academic point of view, I wonder why the smaller discos are not dual rated, since we all know that the real-time voltage difference in a 240 V AC system can be 41% greater than 240 V. In any event, any Code-compliant solutions would be greatly appreciated. - Peter Peter T. Parrish, President
_______________________________________________ List sponsored by Home Power magazine List Address: [email protected] Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
