[RE-wrenches] DC disconnect placement

Walt Ratterman wratterman at sunenergypower.com
Sun Dec 20 21:49:07 PST 2009


Hello all,

 

While this may be excellent advice, I think it would be good to clarify that this may apply primarily to grid tied systems.  

 

In Off Grid systems we have different considerations, such as (a) we are working with lower voltages and need to limit the size of the wire and the voltage drop, and (b) there IS protection at the equipment room on the homeruns from the combiners to the equipment room (assuming the combiners are at the array) as long as we have individual circuit breakers on the input of each charge controller.

 

Thanks,

 

Walt

 

 

Walt Ratterman

SunEnergy Power International

 

11 Laurel Lane South     Washougal, WA   98671

(360)-837-3680   ▪   fax (360)-837-1315   ▪   Skype  Walt-Mobile

wratterman at SunEPI.org   ▪   www.SunEPI.org <http://www.sunepi.org/> 

 

 

 

 

 

 

From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Matt Lafferty
Sent: Sunday, December 20, 2009 4:10 PM
To: 'RE-wrenches'
Subject: Re: [RE-wrenches] DC disconnect placement

 

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

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org/attachments/20091220/fe66ec60/attachment-0003.html>


More information about the RE-wrenches mailing list