Long residential feeder [RE-wrenches]

[Drake Chamberlin]

A Colorado inspector told me to size the feeder for the load.  He stated that performance issues were between the customer and myself.  Different inspectors might have a different take on this. Certainly head room should be left for future expansion.   



On long runs, I'm in favor of running conductors in parallel.  You will use less metal to achieve the desired VD, and the pulling will be a lot easier.



-Drake 



----------------------------------------



				From: William Miller <wrmiller at charter.net>

Sent: Thursday, January 04, 2007 10:37 AM

To: RE-wrenches at topica.com

Subject: Long residential feeder [RE-wrenches] 



Colleagues:



I wanted to see if there is a consensus on the subject of sizing long 

residential feeders.  I have some off-grid jobs coming up with feeders 

anywhere from 350 to 530 conduit feet and I need to specify feeder 

sizes.  Here's the philosophy I have been using, I'd be curious if anyone 

disagrees:



NEC 215.2 A (4) specifies feeders to not exceed 3% VD.  I agree this is 

appropriate for considering VD for the maximum draw I might 

expect.  Furthermore, I imagine that peak current draw will occur 

infrequently (or these customers are going to exceed the capability of 

their systems on a regular basis).



I base my calculations on a maximum draw of 50 amps for the larger off-grid 

residences I am now designing for.  If the VD approaches 3% at 50 amps, it 

is not much above 1% for 30 amp draws.  I figure staying in this range is safe.



Comments from this group are always greatly appreciated.



William Miller



__________________________________________________________________

William Miller

Miller Power and Communications

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