Wire Size Questions for Long Outdoor 10 amp Circuit

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01-03-14, 02:03 PM

SonomaJim

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Wire Size Questions for Long Outdoor 10 amp Circuit

Need to run a 120V/10 amp circuit in 650' of underground conduit. A 5% voltage drop is fine. I am thinking #4 aluminum (USE ??) will do for the two hot conductors. Will #4 work for the neutral conductor as well? Finally, does the equipment ground conductor (assuming I need one) have to be #4 too?

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01-03-14, 02:05 PM

pcboss

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The smallest branch circuit size under the NEC is 15 amps. What are you trying to power? A 120 circuit would only need 1 hot.

01-06-14, 04:12 PM

SonomaJim

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Good catch. I meant #4 for the one hot lead.

I need to power a small motor (< 5 amps).

Same questions then for a 15 amp circuit. #4 for the neutral? What size for the equipment ground conductor? Thanks, jr

01-06-14, 07:24 PM

Tolyn Ironhand

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Using the calculator here: Voltage Drop Calculator

I calculate a VD of 3.75% with #8 copper or 3.88% with #6 aluminum. Your wire size you posted is WAY too big. (calculated using 5 amps)

The ground would also be required to be increased in size.

Last edited by Tolyn Ironhand; 01-06-14 at 07:53 PM.

01-06-14, 07:30 PM

pcboss

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The voltage drop can be figured on the expected load, not necessarily the breaker size. Also be sure to watch whether the calculator asks for the one way or round trip circuit distance.