[RE-wrenches] DC disconnect placement

[Matt Lafferty]

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-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at 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: william at millersolar.com
http://millersolar.com <http://millersolar.com/> 
License No. C-10-773985


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