Long residential feeder [RE-wrenches]

[Ray Walters]

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We use Aluminum URD direct burial for long AC runs; the price just can't 
be beat. Much easier than conduit over 200 ft. When sizing, I also look 
at volt drop during starting surges for pumps, power tools, etc. to make 
sure I'm not dropping below the minimum voltage allowed for the 
particular device. I usually keep  it below 6%, though some things can 
stand a drop to 10% for a couple of seconds.
We just ran 2000 ft for a well pump, voltage at startup at the pump was 
235 vac (from pair of SW 4024s), while the generator used previously at 
the well head wa s dragging down to 210 vac.

Ray


>
>
>
>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.   
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>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.
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>-Drake 
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>----------------------------------------
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>
>				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 
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>residential feeders.  I have some off-grid jobs coming up with feeders 
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>anywhere from 350 to 530 conduit feet and I need to specify feeder 
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>sizes.  Here's the philosophy I have been using, I'd be curious if anyone 
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>disagrees:
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>
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>NEC 215.2 A (4) specifies feeders to not exceed 3% VD.  I agree this is 
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>appropriate for considering VD for the maximum draw I might 
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>expect.  Furthermore, I imagine that peak current draw will occur 
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>infrequently (or these customers are going to exceed the capability of 
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>their systems on a regular basis).
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>
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>I base my calculations on a maximum draw of 50 amps for the larger off-grid 
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>residences I am now designing for.  If the VD approaches 3% at 50 amps, it 
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>is not much above 1% for 30 amp draws.  I figure staying in this range is safe.
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>Comments from this group are always greatly appreciated.
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>
>
>William Miller
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>  
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