Voltage Drop

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jeff43222

Senior Member
Location
Minneapolis, Minnesota
I have a customer who wants me to run a new feeder circuit to her detached garage. The previous owner used NM and direct-buried it several millimeters below grade, and sure enough, it got chewed up in the garden.

She is looking to keep costs low, so she wants it done without any frills. The garage is a single-car, with a few lights, garage-door opener, and a couple of general-use receptacles. My thinking was to direct-bury 14-2 UF, but then I got to thinking about voltage drop, since the total distance from the panel to the garage will be about 100'.

Should I go with #12 wire, or is voltage drop not something I need to concern myself with on this one?
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
Considering the labor involved I can not imagine running less than 12 AWG.

And really I would probably be running a 3 wire so you can provide two circuits with less voltage drop.

But 14/2 would light the lights and run the door opener.
 
C

cpal

Senior Member
Location
MA
Bob has delivered some good advice

circuit length is critical to voltage drop. a rule of thumb albiet not cast in concrete is

Th ampacities listed in table 310.16 work for a distance point to point (not total circuit lenght) that mirrors the voltage.
Or point A to point B 12 gage for 20 Amps 125volts 125 feet or 12 gage at 20 Amps at 250 Volts for 250 feet.

this is ok to give you a heads up to crunch the numbers.

Voltage drop = Amps X twice the length X K / CMA
CMA = cir mil area
K = Specific res per cir mil foot at a given temp
Copper at 20 Deg C is approx 10.4

If the formular is wrong someone will correct it and there other methods

Charlie
 
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