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# 10 AWG for a 120 foot run?

#1
08-18-15, 08:43 PM
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10 AWG for a 120 foot run?

I am planning on running electrical from my breaker panel at the house to a garage. The total run will be about 120 feet. The garage has a refrigerator and a freezer in it, as well as a few lights.

About 20% of the way down the 120 foot run, I want to put an outlet for outdoor use (lights, maybe an electric smoker in the future, etc.)

The 120 foot run will be in conduit and I plan on using outdoor rated wire. The question is, should I use 10 AWG or is 12 AWG sufficient? If I use 10 AWG, what size breaker should I use?

I was thinking about running the 120 foot run as one run, and then doing a separate run along side it for the outlet about 30 feet down the line. Can I connect them both to the same breaker?

#2
08-18-15, 08:51 PM
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#12 should be enough but you may want to consider a multiwire circuit. Put refrigerator and freezer on one side and receptacles and lights on the other.

#3
08-19-15, 01:19 AM
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Regardless of the length of the run any circuit supplying general purpose 120 volt receptacles is limited to a 20 ampere circuit breaker.

#4
08-19-15, 04:10 AM
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You can use #10 to compensate for any voltage drop at the garage, but as Furd posted, you are limited to 20 amps.

I agree with Ray, run a multiwire circuit. The electric smoker will draw about 12 amps alone.

#5
08-19-15, 08:20 AM
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The 10 gauge wire in a 120 volt only circuit (e.g. black, white, green THWN) will support 15 amps before the voltage drop becomes too great in this example.

I suggest running at least 8 gauge wire as a combination 120/240 volt circuit (a multiwire branch circuit) that will give you 120 volt and 240 volt usage up to the equivalent of 40 amps at 240 volts. A garage is large enough that someone someday is going to want to use more than 20 amps @ 120 volts and since you are digging the trench to bury the line now, you might as well plan for the future.

For now you can attach 12 gauge wire scraps (pigtails) to the 8 gauge wires entering the house panel (1) to fit into a 20 amp breaker set and (2) to let others know that the circuit is now limited to 20 amps (on each side if MWBC), and (3) to share the breaker with another branch circuit (q.v. below) and you will not need to install a subpanel in the garage yet.

Twelve gauge pigtails at the breaker, upstream of the 8 or 6 gauge run to the garage will not impair the performance of the fatter wire making the majority of the run length.

You may run a separate 12 gauge line to the outdoor receptacle 30 feet away. You may tie it into the same 20 amp breaker. If this is a 120 volt only circuit it would be preferable to give it a separate breaker.

Last edited by AllanJ; 08-19-15 at 08:36 AM.
#6
08-19-15, 08:35 AM
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Allan, Not sure what numbers you are using for the voltage drop calculations but this is what I got using 12.5 amps for the load (1500 watts):

1 conductors per phase utilizing a #10 Copper conductor will limit the voltage drop to 2.63% or less when supplying 12.5 amps for 120 feet on a 120 volt system.

#8 is overkill IMO

#7
08-19-15, 08:40 AM
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Ten gauge wire has 1.2 ohms per 1000 feet or about 0.3 ohms for 240 feet round trip.

Losing 4 volts (slightly more than 3%) in the wires, we divide 4 by 0.3 ohms to get slightly less than 15 amps.

With a 10 gauge MWBC you get about 25 amps on each side with 3% voltage drop with the sides reasonably balanced.

#8
08-19-15, 12:40 PM
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Thank you for all of the replies! Luckily the garage is very small (would barely fit a car), and I mostly use it to house a refrigerator and freezer for overflow purposes, so I don't foresee a need to have anything at 240V. I am going to price out the #8 wire for the 120' run. Otherwise maybe I'll run two sets of #10, and a third for the outdoor outlet for the smoker and give it another breaker just in case.

#9
08-19-15, 01:54 PM
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Otherwise maybe I'll run two sets of #10
No reason to run two sets. Just run a multiwire, two hots and a neutral.
I don't foresee a need to have anything at 240V.
If you are reffing to the multiwire it is two 120 volt circuits.
Otherwise maybe I'll run two sets of #10, and a third for the outdoor outlet for the smoker and give it another breaker just in case.
You can only have one source of power to the garage so you can't run two circuits to the garage. That is why I suggested a multi wire circuit. It provides two 20 amp 120v feeds but only counts as one circuit.

#10
08-19-15, 02:07 PM
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Ok that makes sense. So at the garage I will wire the fridge/freezer outlets with one of the hots and the lights with the other?

#11
08-19-15, 03:11 PM
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So at the garage I will wire the fridge/freezer outlets with one of the hots and the lights with the other?
Yes. You could also use the other hot for an outside receptacle.
About 20% of the way down the 120 foot run, I want to put an outlet for outdoor use (lights, maybe an electric smoker in the future, etc.)
You could split the multiwire at that point and continue on to the garage with a single 120v 20a circuit. If only a freezer, refrigerator and lights a single 20 amp circuit should be enough for the garage. You would only need #12 to the garage but #10 would give you a bit of a margin. Run conduit with individual conductors not cable and you will be future proofed should you ever need more power.

#12
08-19-15, 03:46 PM
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That's what I'll do! Thank you so much for your help!

#13
08-19-15, 05:44 PM
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Twelve gauge wire to the garage as a single 120 volt circuit will allow about 8 amps at about 3% (recommended maximum) voltage drop or about 10 amps at 4% voltage drop.

#14
08-19-15, 06:24 PM
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My thought was #10 to the outdoor receptacle where it splits off then #12 from there. The calculator I uses show a 4.9% drop for a 15 amp load using #12 and assuming 100 feet. Source: http://www.electrician2.com/calculat...r_initial.html

#15
08-19-15, 07:18 PM
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From my post #6:
1 conductors per phase utilizing a #10 Copper conductor will limit the voltage drop to 2.63% or less when supplying 12.5 amps for 120 feet on a 120 volt system.
This calculation was done using this calculator: Voltage Drop Calculator Note it says "cable run", you do not double the length. I get the same results using this calculator as well: http://www.calculator.net/voltage-dr...12.5&x=67&y=11

I was suggesting running #10 for the whole run to the garage. The OP could just run 1 #12 to the short receptacle for the smoker since it is only about 25' down the line, and then 2 #10's for the other hot, neutral, and of course, ground.

#16
08-19-15, 08:41 PM
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Sf23103, please follow Tolyn's or Allan's suggestions. They are better than mine.

#17
08-20-15, 12:48 AM
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Tolyn Ironhand, I am planning on running #12 to the outdoor outlet and #10/3 to the garage. Are you suggesting running two separate #10's to the garage?

#18
08-20-15, 04:26 AM
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You never did say how (wiring method) you were going to run it, but it might be just as easy to run two circuits if you plan to run UF cable. One to the outdoor outlet, one to the garage.

If you plan to run PVC conduit it would might be easier to loop it through the outdoor outlet. You still can run two circuits (4 wires) as long as you still only have one feed to the garage.

Now to get creative: I would run a 3 #10 wires (plus a ground) for a multiwire circuit from the panel to the outdoor outlet. Tap off one of the hots and neutral for the outlet, and continue all three wires of the circuit to the garage. That way you would have double the capacity in the garage for future use. You would also have 240 volt there if ever needed. All you would need in the garage is a two pole disconnect (two pole switch or A/C pullout)

Whatever you choose, if you use a multiwire circuit you need to install a two pole breaker in the panel, as apposed to 2 single pole breakers if running two separate circuits.

#19
08-20-15, 04:55 AM
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... 1 conductors per phase utilizing a #10 Copper conductor will limit the voltage drop to 2.63% or less when supplying 12.5 amps for 120 feet on a 120 volt system. ...
Correct.

When the draw gets up to 15 amps the voltage drop will be somewhere around 3%.

Running the multiwire branch circuit to the garage actually allows more than twice the amperes (both legs combined) compared with (hypothetically) running two completely separate circuits! With the MWBC, you plug 240 volts into the voltage drop calculator instead of 120 volts.

There may be a derating rule in the NEC for voltage drop on general purpose MWBCs compared with straight 240 volt circuits to account for idiosyncrasies when the load on both sides is or is not balanced, but I am not aware of such a rule.

Last edited by AllanJ; 08-20-15 at 05:11 AM.
#20
08-20-15, 06:33 PM
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The NEC has no requirement regarding voltage drop. It is only an informational note.