[RE-wrenches] Sqd H series disconnects

[Brian Teitelbaum]

Kirk,

Here is the link to the Schneider Square-D white paper on using their HD safety switches in photovoltaic circuits:

http://static.schneider-electric.us/docs/Electrical%20Distribution/Safety%20Switches/Solar%20Disconnect%20Switches/3110DB0401.pdf

Figure "1D" shows the common use of these switches with two poles in series to get the 600VDC and full amperage ratings. If you use the non-fused version of the switches, you only need to multiply the Isc of the array by 125%, so the 30A switch should work for you (22.64A x 1.25 = 28.3A). If you need to use the fused versions, then you will need the 60A switch (22.64A x 1.56 = 35.32A) because the fuses and fuse holders are only rated at 80% duty.

By using two poles in series, you are creating two breaks in the circuit which substantially raises the current-carrying capacity of each pole, at least as far as load-break is concerned.

Also note that using a single pole per string, the non-fused 30A switch is rated at 16A Isc per pole. However, the switches are not UL Listed for that purpose. They are only "Self Certified" by Schneider in that configuration. That may cause some grief with some inspectors.

Brian Teitelbaum
AEE Solar


From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Kirk Herander
Sent: Monday, March 19, 2012 1:41 PM
To: RE-wrenches
Subject: [RE-wrenches] Sqd H series disconnects

Hello,

I am combining -4- series strings at the array in a series-fused combiner. The sum Isc of the four strings is 22.64 adc. I want to use either a HU361(30 amp) or HU362(60 amp) as a disco at the inverter instead of running individual strings a long distance from the arrays to the factory-supplied SMA fused disco. So the Isc rating for the HU361 Is 11.5 amps per pole, the HU362 is 38 amps per pole. Although not clear in the SQD datasheet, I think that if two poles are series together the DC(non-pv dc) rating is a full 30 amps for the HU361, and 60 amps for the 362. But the limiting factor in a PV application is the per-pole Isc rating, regardless of putting 2 poles in series (this does not increase the Isc rating of the respective disconnect), correct? I'm assuming my only choice in this instance is to use the 60 amp disco?

Kirk Herander
VT Solar, LLC
dba Vermont Solar Engineering
NABCEPTM Certified installer Charter Member
NYSERDA-eligible Installer
VT RE Incentive Program Partner
802.863.1202

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