1 edit | Voltage drop and upsizing wire @150 feet from breaker panel I have a friend who is planning on running two 20 Amp circuits 150 feet from his breaker panel and there is debate as to whether or not he needs to increase the gauge of the wire from 12 gauge to a thicker gauge to account for the resistance of the wire at this distance. Over the years I have read many great posts on this forum from knowledgeable people with years of experience and I was hoping that someone could tell me if he needs to upsize the wires and if so what size wire should he use? |
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iknowPremium
join:2012-03-25 | Re: Voltage drop and upsizing wire @150 from breaker panel said by sneakaround:I have a friend who is planning on running two 20 Amp circuits 150 feet from his breaker panel and there is debate as to whether or not he needs to increase the gauge of the wire from 12 gauge to a thicker gauge to account for the resistance of the wire at this distance. Over the years I have read many great posts on this forum from knowledgeable people with years of experience and I was hoping that someone could tell me if he needs to upsize the wires and if so what size wire should he use?
according to »www.csgnetwork.com/wiresizecalc.html #8 wire |
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 tschmidtPremium,MVM
join:2000-11-12
Milford, NH
kudos:8
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Should limit voltage drop on branch circuits to 3%, less is better.
Here is link to Siemens spread sheet to calculate voltage drop:
»www.google.com/url?sa=t&rct=j&q=···J-N5miEA
/tom |
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JoelC707Premium
join:2002-07-09
West Point, GA
kudos:5 | reply to sneakaround
You'll actually need 6 AWG. The link iknow posted says this as well. I suspect he entered 75 for the "one half total circuit length" field and 150 should have been entered here as well. This is because the circuit also has to travel back to the panel so the actual total circuit length is 300 feet for a 150 ft run.
6 AWG according to the spreadsheet posted will give 2.5% drop or 2.9V drop.
8 AWG would give 3.9% drop or 4.7V.
The "nominal" 12 AWG would give 9.9% drop or 11.9V. |
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 leiboldPremium,MVM
join:2002-07-09
Sunnyvale, CA
kudos:6
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| We don't know what is at the destination of that 150ft run but if it is some kind of structure it makes sense to consider installing a subpanel (for future proofing).
The same #6 120V 20A wires can be used to feed a 240V 40A subpanel and therefore the only additional cost is the subpanel itself and a dual-pole 40A breaker in the main panel. The two 20A breakers for the circuits are needed in either case (the only difference being whether they are installed in the main panel or the subpanel).
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| I like the idea of the sub panel, my friend's original plan was for a sub panel actually. He had gotten some bad advice and wound up installing only a 3/4" conduit underground to his garage.... I believe he should be able to install four 6 gauge wires in that conduit, 2 hot (220), 1 neutral, and 1 ground. His needs are one circuit for a pool pump and another for lights, radio, etc... |
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JoelC707Premium
join:2002-07-09
West Point, GA
kudos:5 | 3/4" EMT/IMC/Galvanized is limited to four 6 AWG THWN/THHN conductors so you just do have enough room in that conduit for that plan. References: »www.westernextralite.com/resourc···p?key=47 »www.elliottelectric.com/StaticPa···ble.aspx |
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 alkizmo
join:2007-06-25
Pierrefonds, QC
kudos:1 | reply to iknow
I'd take the calculator link's answer with a grain of salt.
If you put 30A with 10 feet circuit, it says you can use 14AWG. Sure you can, code won't allow it though.
And my 15A circuits that go 45 feet away from the panel (90 feet full circuit) would require 12AWG according to the calculator. Guess what, 45 feet is not that much when your panel is in the basement and you're supplying bedrooms 2 floors up (With the wires circling around the house, going through the attic, etc). |
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 whizkid3Premium,MVM
join:2002-02-21
Queens, NY
kudos:9 | reply to sneakaround
Re: Voltage drop and upsizing wire @150 feet from breaker panel The answer is yes; the wires should be up-sized. The questions are: what is the load; what type of raceway (i.e. PVC or steel conduit); and what is the power factor of the load? All of these have a bearing on the voltage drop.
If you are talking receptacles (i.e., 15A duplex receptacles), it is common to use 80% of the circuit breaker size in voltage drop calculations, which is 16A. On the other hand, if the 20A circuit is being run to feed a 1/2 hp pump, then the load is small enough that the wiring does not need to be increased to accommodate the voltage drop. In the case of duplex receptacles, using 16A as the load; one would want to upsize the wire to 6 AWG to avoid more than 3% voltage drop.
(While we appreciate the Siemen's voltage drop calculator, tschmidt  , it doesn't allow one to specify the type of conduit, the power factor of the load, nor the desired maximum voltage drop.)
FYI - if this installation is on Staten Island, note that while there is no code requirement for voltage drop in the NEC; the NYC Electrical Code requires a maximum voltage drop of 3% for branch circuits. |
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scooper
join:2000-07-11
Youngsville, NC
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While I respect whizkid's knowledge as a pro electrician - as a pool owner I'd suggest that what the calculator is giving should be considered a minimum as far as the pool pump and related equipment is concerned. Pool pumps are not very tolerant of voltage outside of spec (above or below) and will run hot, if not shutdown due to thermal overload. The AWG 6 is a minimum I would want to use, and make sure your wiring from the subpanel to the pump is also large enough. The good news is that using 240V on your pool pump is definately a plus, as most 1-2 HP pumps will draw from 3-10 Amps on 240v (double the amps if using 120V). |
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alkizmo
join:2007-06-25
Pierrefonds, QC
kudos:1 | said by scooper:While I respect whizkid's knowledge as a pro electrician - as a pool owner I'd suggest that what the calculator is giving should be considered a minimum as far as the pool pump and related equipment is concerned.
Whizkid was saying that there isn't enough info on the load.
A 20A circuit doesn't represent what is the load. |
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 John GaltForward, MarchPremium
join:2004-09-30
Happy Camp
kudos:5 | reply to sneakaround
Sparky uses charts in the NEC...not necessarily what is marked on the motor. |
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whizkid3Premium,MVM
join:2002-02-21
Queens, NY
kudos:9 | reply to scooper
said by scooper:I'd suggest that what the calculator is giving should be considered a minimum as far as the pool pump and related equipment is concerned. Pool pumps are not very tolerant of voltage outside of spec (above or below) and will run hot... The NEC recommended voltage drop (or code mandated voltage drop requirements in some jurisdictions) are only a starting point. Nothing says that a demanding installation doesn't warrant a lower voltage drop. Motors are normally designed for a lower voltage than the nominal voltage to account for this; i.e. 115V for motors on 120V circuits. 230V for use on 240V circuits, etc. If one is going all out, you should do two voltage drop calculations for motors - 15% voltage drop minimum for starting current (don't forget to find out what the power factor is at start-up - it can be 25%); and 5% (total feeder & branch circuit) for running load amps. At least in a home, there often isn't too much 'feeder' voltage drop; and a 3% total voltage drop is really not too shabby. But yeah - feel free to add more copper (or even a buck & boost transformer). 
said by John Galt:Sparky uses charts in the NEC...not necessarily what is marked on the motor. Agreed. Especially considering its a code requirement to use the NEC article 430 tables - not the nameplate. No one knows what kind of crappy motor someone is going to replace it with later. |
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| reply to whizkid3
said by whizkid3:The answer is yes; the wires should be up-sized. The questions are: what is the load; what type of raceway (i.e. PVC or steel conduit); and what is the power factor of the load? All of these have a bearing on the voltage drop.
Thank you everyone for the replies. He is planning on running the circuits in PVC, the current pool pump runs on 120V and he has no plans on replacing it until it dies, the other circuit is a utility circuit for lights radio and occasional tool use.
Based upon the responses so far I will tell him that he should run 6 gauge wire. |
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