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wire size #173977 01/24/08 02:35 PM
Joined: Jan 2007
Posts: 59
dilydalyer Offline OP
I am doing a job for a guy at church.He has a shed 169 ft from his house.He has a few flourescent lights and a welder 21 amps.Me and a buddy have done the calculations but I wanted your opinion.Not taking the future into account,which the owner says don't worry about(:)),should I not pull 10 to save him money?Also,not downsize nuetral?

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Re: wire size [Re: dilydalyer] #173978 01/24/08 03:31 PM
Joined: Jul 2004
Posts: 625
SolarPowered Offline
I'm not sure if the Code will allow this, but I would want to run two lines out there, one for the welder, and one for everything else, so that you don't have the lights dimming up and down (as much) from the welder.

Re: wire size [Re: dilydalyer] #173979 01/24/08 03:37 PM
Joined: Dec 2003
Posts: 751
earlydean Offline
assuming 240 volts, 3% VD would be 7.2 volts
VD = 2 x I x L x R / 1,000, using the R per 1,000 feet in Table 8, Chapter 9.
Transposing: max R = 1,000 x 7.2 volts / 2 x I x L
L = 169 feet
I = 21 amps (or 25 amps with lights?)

so max R would be 1.1 to .85 ohm which means a #8 copper conductor would be required. (.809 ohm per 1,000 feet)
Neutral could be downsized for 240 volt load.

If you are running 120 volts, then maximum VD would be 3.6 volts.
and max R would = 1,000 x 3.6 / 2 x 25 x 169 = .42 ohm, which corresponds to a #4 copper conductor.

If you run less, you risk low voltage to appliances. Problem??? maybe, maybe not.

Re: wire size [Re: earlydean] #173985 01/24/08 06:34 PM
Joined: Jan 2007
Posts: 59
dilydalyer Offline OP
As usual,I left out info:(..The welder is 230 volt,3 prong outlet(I am pulling 2 hots,nuetraland ground....thks

Re: wire size [Re: dilydalyer] #173989 01/24/08 08:05 PM
Joined: Jan 2003
Posts: 1,429
LK Offline
I am trying to figure how you are going to same him money, he needs a 18 in deep trench and a lot of PVC and wire, hope he is getting a permit for this, if the job is done shabby and it leaks current to the neighbors property watch out. I would not even be a thing of saving money, but doing it right.

Re: wire size [Re: LK] #174001 01/24/08 09:52 PM
Joined: Jan 2007
Posts: 59
dilydalyer Offline OP

yeah,LK,WE have a permit and there is an existing conduit.1000' no 8 270.oo,1000 no 10 140.oo.I intended to pull 8 from the start but thought I'd discuss the load and wire size among friends....Leaking current???????????

Re: wire size [Re: dilydalyer] #174003 01/24/08 10:19 PM
Joined: Jul 2004
Posts: 9,554
gfretwell Offline
I think the welder is such intermittent service I would not get too crazy about it. When you have your mask down you won't see the light dim anyway. If he really thinks he will be adding a lot more load, then go with the #8 but 10 should be fine.

Greg Fretwell
Re: wire size [Re: gfretwell] #174004 01/24/08 10:31 PM
Joined: Dec 2002
Posts: 228
JCooper Offline
I would really consider a second circuit for the light, if he runs the welder too long and pops the breaker, he will be in the dark with a really hot piece of metal in front of him.

Re: wire size [Re: gfretwell] #174006 01/24/08 10:37 PM
Joined: Jul 2007
Posts: 265
wire_twister Offline
Whatever you do he Will outgrow it, like a gold fish people expand to fit the size of their surroundings, I would present him with the prices and lrt him make the call. Personally I feel bigger is better, I would try to sell him some 6awg wire just to have the headroom. Greg is right on the nose with the welder, I have one that Hobart says needs a 50a breaker to run, been running it on a 30 for 3 years and never had a problem. Low amps and light duty cycle equals low required current.


Life is tough, Life is tougher when you are stupid
Re: wire size [Re: dilydalyer] #174054 01/25/08 07:06 PM
Joined: Jan 2003
Posts: 1,429
LK Offline
Leaking current better known as stray, comes from various sources, poor substation grounding, bad power distribution designs, shabby underground work.

Every year we get calls I am getting a shock when I walk in the back yard, or when I touch the chain link fence, usually when we get to the job we may find a backyard shed that has been wired by a DIYer, and it usually had shabby wiring with faults causing us to get stray readings.

Hope this helps you understand, leaking current.

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