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Hi,The manual of my welder recommend a 50 amp circuit on a AWG 12/3 wire and 90 ft max.I would like to set my things up in a shed at around 150 ft of my main circuit box. I already have a 15 amp circuit on an AWG 10/3 underground cable. What are my options? Running another bigger gauge cable from my main box?All the best,Sam
Reply:Sam, from the NCE.50 amps to 150 feet120 v, #2 145 ft; #1/0 230 ft.240v,  #6 105 ft; #4 182 ft.Now that takes care of the welder. What about lights, coffee pot, etc.?I think you’re looking at a 80 amp 240/120 panel minimum using #2 four conductor cable.
Reply:Originally Posted by samueltcHi,The manual of my welder recommend a 50 amp circuit on a AWG 12/3 wire and 90 ft max.
Reply:Keep in mind the duty cycle "derating" is only for the welders dedicated circuit. If you are running anything else on the same circuit (lights, compressor, fans etc.), forget the derating factor for the feed to the shed.That being said, I screwed up when I wired my shop. I'm running a 100 amp sub panel fed from the house with #4 copper. I should have used #2. Where I made my mistake was a misinterpretation of the NEC. I used the 90 degree C rating of the wire instead of the 75. (Your circuit should be rated for the weakest link, and my panel and breakers are only 75 degree C rated, therefore the wire is too small.) I've checked temperatures inside my panels at the screw terminals of the breaker feeding the shop while running my 250 amp TIG machine, and haven't seen any heat buildup.It's still wrong, and it will bother me till I fix it. The lesson is, make sure you know what your doing, or consult someone who does and do it right the first time. I'm going to end up with about 400 feet of used #4 copper that will have to be replaced with #2 at todays copper prices, instead of what it cost back in 1997. I might actually have to dig up and replace the conduit buried 24" down, as I don't think I sized it big enough for 4 runs of #2.Which brings up my own question for the experts: At the time I built my shop, it was my understanding because it was a sub panel, I had to run a ground circuit back to the main. (Something about all grounds having to be tied to the same point to avoid possible voltage potentials between them.) Is/was this true, or can I ground the shop separately and just run the two hots and a neutral between the shop and the house?Miller Thunderbolt AC/DC (Sold)Miller Dialarc 250HFMiller MM251Miller MM200 (Sold)Miller MM130Miller Spot WelderVictor O/A rigMiller Spoolmatic 1 (Sold)