Running electrical 250'

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rpdwyer

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Hi All.

I want to run 30 amps to my work shed about 250 feet from my house panel. It currently has a 60 AMP subpanel that I usually power with a generator. I've got an electric heater in there and some power tools including a wood lathe, saws, bench drill and bench grinders. I believe I can run two hot legs to it via 6 AWG, correct? Would you recommend a larger gauge wire? In addition to the two hot legs the neutral and the ground both need to be the same gauge as the hot legs, correct?

My original goal was to shoot for 60 amps so I could potentially power a Lincoln sticker welder but guage wire needed to do that seemed prohibitively expensive.

Thanks in advance.

--Rick
 
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Dana

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Hi All.

I want to run 30 amps to my work shed about 250 feet from my house panel. It currently has a 60 AMP subpanel that I usually power with a generator. I've got an electric heater in there and some power tools including a wood lathe, saws, bench drill and bench grinders. I believe I can run two hot legs to it via 6 AWG, correct? Would you recommend a larger gauge wire? In addition to the two hot legs the neutral and the ground both need to be the same gauge as the hot legs, correct?

My original goal was to shoot for 60 amps so I could potentially power a Lincoln sticker welder but guage wire needed to do that seemed prohibitively expensive.

Thanks in advance.

--Rick

Yes, the neutrals need to have the same capacity as the the supply.

Limiting it to a 2% voltage drop at 30A across 250' of wire takes #1 AWG wire. If you can tolerate a 5% drop @ 30A it takes 4AWG as a single wire.

A pair of #6AWG wires at (15A + 15A=) 30A would deliver a 4% drop in voltage at 250'. Play around with this freebie online calculator and this one bit.

You may want to bump that to a pair of #4AWG if there are any big motor-loads on that equipment. Split capacitor AC motors draw substantially more on startup than their normal current under load. Typically it takes wire ampacity 25-35% greater than the steady state load to guarantee good starting characteristics for motors. If it's marginal it can overheat & burn up the motors under worst-case conditions.
 

wwhitney

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Yes, the neutrals need to have the same capacity as the the supply.
I don't agree, for a feeder, the neutral just needs to have sufficient size for the calculated neutral load, and be at least as large as the minimum size EGC allowed.

Why not use something like 2-2-2-4 Al mobile home feeder cable? You could put that on a 50A breaker and comply with the EGC "upsized for voltage drop" rule. Or you could jump up to 1/0, 2/0, or 4/0. I'm assuming you're burying the feeder; PVC conduit is likely worth it rather than depending on direct burial.

Cheers, Wayne
 

Reach4

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Limiting it to a 2% voltage drop at 30A across 250' of wire takes #1 AWG wire. If you can tolerate a 5% drop @ 30A it takes 4AWG as a single wire.
More often than not, my power company voltage is more than 5% above nominal to start with.
 

rpdwyer

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Why not use something like 2-2-2-4 Al mobile home feeder cable?
Cheers, Wayne

I will more accurately measure the distance but it appears that if I'm around 250', using feeder cable I can get at least 2 legs of #2 30 Amp, a #2 neutral and a #4 ground. Does this sound correct? I wanted 50 or 60 amps so I could run a welder but it looks like i would have to go with copper for that and that stuff is $$$.
 

wwhitney

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The calculators Dana pointed us toward are giving me slightly different answers than Southwire's calculator https://www.southwire.com/calculator-vdrop

But for 2-2-2-4 Al, you could definitely draw 40 amps with only a 3% voltage drop. You could put it on a 50A or 60A breaker because you wouldn't actually be drawing over 40A very often (if ever) and your loads may be able to tolerate a larger voltage drop when you do. Or you could bump up to 1/0-1/0-1/0-2 Al and a 60A breaker.

A couple things to be aware of: If you get a cable that is only listed as URD (and not dual listed as XHHW or RHW), then the cable is not actually allowed to enter either building, it needs to stay outside. And depending on the breaker size, the breaker may not accept #2 or #1/0 conductors. A solution to both problems is to plan on a splice box on the outside of each building, where you transition from an indoor wiring method to the outdoor Al feeder, and also transition sizing as required for the breakers.

Cheers< Wayne
 

rpdwyer

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The calculators Dana pointed us toward are giving me slightly different answers than Southwire's calculator https://www.southwire.com/calculator-vdrop

But for 2-2-2-4 Al, you could definitely draw 40 amps with only a 3% voltage drop. You could put it on a 50A or 60A breaker because you wouldn't actually be drawing over 40A very often (if ever) and your loads may be able to tolerate a larger voltage drop when you do. Or you could bump up to 1/0-1/0-1/0-2 Al and a 60A breaker.

A couple things to be aware of: If you get a cable that is only listed as URD (and not dual listed as XHHW or RHW), then the cable is not actually allowed to enter either building, it needs to stay outside. And depending on the breaker size, the breaker may not accept #2 or #1/0 conductors. A solution to both problems is to plan on a splice box on the outside of each building, where you transition from an indoor wiring method to the outdoor Al feeder, and also transition sizing as required for the breakers.

Cheers< Wayne

Cable like this qualifies to enter both premises?
1/0,1/0,1/0 & #2 Notre Dame Underground Secondary Distribution Cable
 

wwhitney

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I've not used it myself, but my information is that some is URD only (outside only), some is dual listed URD and RHW (or URD and XHHW). If dual listed, it would need to be in conduit inside. Outside, it can be direct buried (with just the emergences to grade sleeved in conduit) or run in buried conduit (which has advantages). So you need to read the print on the cable itself, or determine the manufacturer and check the data sheet. If you go with junction boxes on the outside of the structures, type SER cable would be a good option to transition to, if you don't want to run conduit inside.

Pay attention also to the minimum cover requirements in NEC Table 300.5 (cover requirements, so 18" cover for a 2" OD conduit requires a minimum 20" deep trench).

Cheers< Wayne
 
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