upgrade garage electric, is it possible?

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  #1  
Old 12-19-12, 04:18 PM
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upgrade garage electric, is it possible?

Hey everyone,

Long time lurker and first time poster. I have a small glass studio in my detached garage and I would like to upgrade my electric. Its time to step up to a larger 240v kiln and replace the 120v I have now.

The garage-shop is currently fed from the house by a 20amp breaker from the main panel in the house. My current kiln runs about 14amps. My ventilation, lights, the occasional power tool, and in the summer my 42" big air fan all run with no problems.

All of the new kilns I'm looking into are in the 14-20amp @ 240v range. The kilns are digitally controlled and run at full load for about 30-45 minutes and then cycle on and off throughout the work day, about 6-7 sec on and 2-3sec off.

My main panel is 100amp service. The panel currently contains;
4 20amp
4 15amp
1 double pole 50amp
1double pole 35amp

The 50amp connects to sub panel Marked "range" which contains 2 more double pole 50 amp breakers. One which controls the range and the other...I really don't know what it does...they are both connected to really heAvy gauge wire but I can only trace one back to the main panel.

I need to run about 70' of wire, and in the end only really need 2 circuits in the garage, a 120v 20amp and a 20amp 220v that will only run the new kiln. I'd like to be able to run the old 14amp 120v as needed if I have another artist or need to fire decals etc. Since the current setup all runs off of a 20amp I can't see needing anymore than the 2 circuits.

In the summer with laundry, stove, central air, and the shop cranking at full I haven't had any problems with electricity.

I've been told run a 60amp sub panel and I've also been told just to run a 10/3 underground burial cable from a double pole 20amp out to the shop in a new trench.

I have a journeyman electrician who I'm trading skill/knowledge with to help with the install.

Is it possible? Up to code? Legal? Upgrading to 200amp is not an option until we find a new home.

I appreciate all advice and will try to answer questions as quickly as I can. I came out better than expected this year and can afford to do some upgrading but want to make sure that the upgrade to 240v is even possible before ordering new equipment.

Thanks and happy holidays.
 
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Old 12-19-12, 04:33 PM
ray2047's Avatar
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I've been told run a 60amp sub panel
A 30 amp subpanel should be more then enough. You would either use 10-3 UF cable buried 24 inches or conduit buried 18" with four #10 THWN wires. I would suggest conduit because it would be easy to increase your power should you ever want a bigger kiln.

While you said you wanted only two circuits it would be almost as cheap to go with a 100 amp main breaker panel for you subpanel and that would give you plenty of future proofing. You would need to add a ground bar (sold separately) to the panel and you would need a ground rod at your shop. The100 amp main breaker that comes with the panel would serve as the code required disconnect.

It would be best to come off the main panel. You would need a 30amp 2-pole breaker.

The existing 20 amp feed would have to be abandoned because code does not permit two feeds to the building. That would free up one of the two spaces you would need for the new breaker.

For a little more you could go to 40 amps using #8 and a 40 amp breaker at the house. That would give you a decent fudge factor.
 
  #3  
Old 12-19-12, 06:52 PM
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To add to Rays comments. You can only have one circuit or feeder to the outbuilding. Since you want both a 120 and a 240 volt circuit at the garage you will need to run a feeder and install a subpanel.

If you run a oversized conduit between the panels you could upgrade the wiring at a later date. I think I would run at least a 40 amp feeder in a 1" conduit.
 
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