William, Put the inverters at the array. Run the AC underground. If the AC feeder gets dug up by some rowdy backhoe operator in the future, the breaker (or series of breakers) will open, de-energizing the circuit immediately (and maybe the main to the residence at the same time). If you are dead-set on putting the inverters in the pump shed, put any combiner(s) at the inverters. This affords the maximum overcurrent protection for the underground feeders. Install DC disconnecting means in each string before leaving the array if you go this route. For maximum protection of conductors and to minimize arc hazards, The SAFEST location for a combiner is ALWAYS at the inverter. All conductors on the inverter (load) side of a fused combiner are unprotected by anything other than their ampacity rating. If a fault occurs on the load side of a combiner, it will burn until it clears or welds to a dead short. Cheers, Matt Lafferty
_____ From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of William Miller Sent: Sunday, December 20, 2009 11:02 AM To: RE-wrenches Subject: [RE-wrenches] DC disconnect placement Friends: I am embarking on a 10 Kw ground mount grid-tie installation. The client prepared for this installation some time ago by stubbing a PVC conduit underground towards the future location of the PV array. Prior to beginning this job, an excavation contractor intercepted the empty conduit with a backhoe. No harm was done because this conduit was empty. Had this conduit been filled with PV feeders, it would have been very necessary to be able to disconnect the PV arrays, both for safety and to prevent a brush fire in our very dry climate. The inverters will be located in a pump house about 130 feet from the PV arrays. I would not normally put disconnects at the array and they are not required. This scenario, however, has caused me to reconsider. The design now calls for a disconnect at each row of modules. I feel that it would not be prudent to delete this important safety item. I wish there were a better selection of compact, low profile disconnects suitable for a roof-top installation. I have put external handle disconnects on roof but they look terrible. I may specify touch-safe fuse holders inside of a Sola Deck for future comp roof jobs. I am not sure what we will do with tile roofs. It seems to me that every source of power should have a means of disconnection as close to the source as possible. This is just common sense. William Miller Please note new e-mail address and domain: William Miller Miller Solar Voice :805-438-5600 email: will...@millersolar.com http://millersolar.com <http://millersolar.com/> License No. C-10-773985
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