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My garage is between 80 & 100 ft. from the main panel . In the garage will be 2-3 flourecent lights , a 17,000 btu 240 volt heater , eventually a welding machine (either 240 volt or a 120 volt inverter , have not decided yet ) let`s go with 240 volt for this question , and 4 120 volt outlets . what size wire should I run to the garage and from what size breaker off the main ?

  • Depends on how much you're willing to spend. I usually recommend 60 amperes for a garage, but for a bit more money you could go up to 100 amperes. What size service feeds the house? See also this answer – Tester101 Apr 10 '16 at 15:36
  • It's not as easy as simply asking what size wire. Asking what size feeder is first and foremost. That heater alone is good for 20A @ 240V. A welder is potentially 30-50A @ 240V. Just calling it a "welding machine" doesn't tell us much. A smaller mig will be in the 20-30A draw @ 240V. A tiny unit could be 20A @ 120V. The lights and general receptacles are almost incidental and will not really affect the feeder size. I'd agree with Tester and say 50-60A minimum, with a 90/100A feeder being optimal. What kind of wire were you thinking? Are you running conduit? How is access to the main panel? – Speedy Petey Apr 10 '16 at 18:13
  • the " welder " is a Lincoln 220 amp , 240 volt . My house panel is 100 amp, my sub panel is 100 amp but I could drop the amperage on that , the breaker off the house panel is 50 amp , but that can also be changed if need be . And the heater is 240 volt . After measuring , the distance is almost 80 ft. – M . Forrester Apr 10 '16 at 19:27
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The 225A welder would draw 50A @ 240V on it's maximum setting. The 17,000 BTU/hr heater is electrically equivalent to 5kW, so about 21A @ 240V. If you want to operate both simultaneously plus lights (not much power required for those, however), you need a 100A subfeed to your garage.. 60A will not cut it.

A 100A subfeed to the garage requires 3/3 AWG NMD if the garage is attached and the cable is protected and not in a wet location. If the garage is separate, then you're looking at running conduit, with 3 AWG RWU90 line and neutral conductors, (minimum 6 AWG neutral conductor if your locality lets you run a reduced neutral), and a 4 AWG ground.

The breaker would be 100A, unless you can find one that's larger than 70A but less than 100 A. You will likely want to upgrade your service to 200A (Imagine someone using the stove and electric clothes dryer while you weld in your heated garage…) In my jurisdiction, a load calculation would result in a 200A service being required.

  • +1 However, conduit is one option but direct burial cable could also be used for a detached garage. Circuit breaker sizes step by 10's from 40 to 110 so 80, 90, or 100 are standard sizes but the most popular is 100. If the OP has gas appliances a 200 amp service upgrade may be un-necessary. (The OP didn't say what the appliances were.) So, depending on the size of the house, the load calculation may still result in a 100 amp service. – ArchonOSX Jun 21 '16 at 1:46
  • Agree. Direct burial of the appropriate NMW or SE (with appropriate protection, as required) or even TECK cable is also an option. In my jurisdiction, a range and dryer are included in the load calculation whether or not they exist, or are gas or electric. These are considered "basic loads" because the next home occupant could choose to have all-electric appliances, and the CEC wants to ensure the electric system is properly sized in any reasonable case. – AndyW Jun 21 '16 at 15:51

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