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| Subject - Garage Service | |
| daustin | I am helping out a rural family whose husband/father/handyman recently passed. His project was running electricity to a detached garage. The house panel is maxed out, but there is a pole on their property requiring a run of 425' to service the garage. The oldest son is in a vocational school welding program and will need a 220v 50 amp line in the garage. 100 amp service total. The owner had purchased 3/0 alum service cable for the hook up. I am used to using copper cable, though alum is common as service cable in this area. I am worried that this may not be sized large enough, creating excessive voltage drop. The family is short of cash, but I may be able to get some others to help out and get the approipriate cable. Pls advise as to your thoughts as what would be optimum, and also acceptable. I am a government electrician on a federal installation. I usually work on ship board systems. Thanks for your thoughts. |
| Mike Delaney | The voltage drop calc goes like this.. K * I * L * 2 / VD k = 21 (for aluminum), I = Load Amps, L = Length, * 2 = there and back, VD = Voltage drop 21 * 100 * 425' * 2 / 7.2 247,916 CM which means you would need 250 alm, 2 wire sizes bigger than 3/0. Your load amps is not necissarily 100 amps, that is your service size, you may only draw 75 amps total in which case you could pull 4/0 alm. Aluminum is fine for service entrance conductors, and also more cost effective. |
| JimmyDee | Just to add my 2 cents here, I ran a #6 cable for my welder many years ago with the belief that the welding company was correct in their figures as to the input amperage of my welder. I already had a 2 pole 30 amp breaker installed and thought I'd use it until the next payday when I could get a 50 amp one. I had a small welding job to do so I fired it up. Breaker didn't trip. Since that time, I've cranked it right up to max for cutting and heavy welding with out tripping. I would say I've been running on the 30 amp for over 20 years and when I replaced my panel a few years back, I rewired it to a 30. So what am I saying? If you have the 3/0, I'd go ahead and install it and never look back. The 50 amps is probably never going to be reached unless you are using a commercial welder and going to be doing welding with 3/16 rod. And even then, so what if you drop a few volts, just crank the welder up a bit and it will compensate for it. Jim |
| Pierre Belarge | Jimmy Was your run 425 feet? Pierre |
| daustin | Yes the run is 425 feet. Thanks to all for the information. I enjoy reading this site, now directly benifiting from it. |
| JimmyDee | quote: Nope, but the point I was making is estimating the voltage drop on 50 amps for a welder that is not a big commercial rig that is being used for welding truck beams is not a realistic amperage. Power company will run runs like this with smaller than 3/0. The 200 amp service on had on my original house that was total electric, was fed underground by 1/0 and that was well over 200". I'm not saying the installation will meet any type of voltage drop standard but if I had a coil of 3/0 AL in my garage, you can bet I'd be using it for that type of load with no worries. Jim |