3.2 % Voltage Drop Calculation

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mphillipps

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I've been invited to bid on a project with a installing a new 50 amp sub panel 250' away from the service entrance. My VD calculation is at 3.2 %.
Do I need to adjust the awg to correct to >3% ?
 
mphillipps said:
I've been invited to bid on a project with a installing a new 50 amp sub panel 250' away from the service entrance. My VD calculation is at 3.2 %.
Do I need to adjust the awg to correct to >3% ?
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IMHO I would bring up the the issue to the owner or engineer on the project and let them decide. If I remember right, the 3% is a fine print note. I know that as electricians we use it all the time but there might not be enough vd on the feeder for the main to effect the 5% over all.
 
Remember voltage drop is a suggestion and not neccisarily enforcable unless you have an engineering spec you are following. I personally would not worry about 3.5% vs 3% and probably not even 5% depending on the type of load. A single 50 amp hard starting motor may cause more than a 19% drop on a #2 AL at that distance.
 
VD recommendations in the NEC are just that, nothing more.

I wouldn't worry about it, on any given day the POCO may be supplying 3.2% overvoltage. :grin:

I know of some 480 volt services that have never been below 500 volts at the service gear.

Roger
 
Follow up detail:
No engineer.
Residential, new construction of small pool house (one room + bath), low voltage land scape lights and pool equipment, pump motor. Heat via propane gas.
 
mphillipps said:
Residential, new construction of small pool house (one room + bath), low voltage land scape lights and pool equipment, pump motor. Heat via propane gas.
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With that being the case, I really wouldn't worry about 3.2%

Roger
 
It doesn't apply in this case, but just so everyone is aware, ASHRAE 90.1 has a mandatory provision that requires that branch circuit voltage drop not exceed 3% and feeder voltage drop not exceed 2%.
 
DetroitEE said:
It doesn't apply in this case, but just so everyone is aware, ASHRAE 90.1 has a mandatory provision that requires that branch circuit voltage drop not exceed 3% and feeder voltage drop not exceed 2%.
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Yup. There are also agencies with their own requirements. I've had to comply with the NIH DRM before - good times!
 
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