[Coco] Powering a computer room/ham shack?

[Frank Swygert]

Running a 20A 220 circuit on 12 AWG is fine (two hots and one neutral). That's really all you need to worry about. Run the 20A 220 to a small sub panel. You'll only find 125A sub panels at Lowe's and such, but again, that's not a problem. I don't know how many circuits you can run, but as long as you don't exceed the 20A draw you're fine. Most sub panels are run with a 30A or higher breaker, but they are run with more draw in mind than what you have. I have a six breaker sub panel run in my house but with a 50A 220V breaker in the box. I have 5 20A and 1 15A breaker in the sub panel. This is just to divide lighting and zone the outlets. The 15A breaker is for the lights, probably no more than 1A draw with just over 100 watts of lights -- compact fluorescents -- and that's if all are on at the same time... well, cut the ceiling fan on and it might pull 2-3A. I don't know what the percentage over the main breaker for the sub panel is (in your case a 20A), but I know it's at least twice the amount. If you're just putting 2-3 15A breakers and 15A outlets in you're more than covered. 

You might want to just run 1 220V receptacle in a box with the spare circuit until the inspector leaves. Then replace the receptacle and box with a sub panel and 3-4 15A outlets, either each on their own breaker or a pair on each breaker. I'm not recommending you do something unsafe, as the 20A breaker will blow if you overload. It just makes it easier for you to do without explaining anything. The inspectors usually take the tack of "if you sell the house the new owners won't know and might just stick a bigger breaker in." My thought is if they're that stupid they're likely to screw something else up and burn the house down too, you can't idiot proof everything! 

Most just don't run less than 30A to a sub panel, but your idea is more to spread the load around, not put more than a 20A load on it. You'll only have a problem if you start tripping the 20A 220V breaker. No electric heaters down there!! Legally, you can work on your own wiring, just not if it is a rental or commercial space (at least in most states). 

#12 wire is good for 20A. http://www.electrical-online.com/cableandwire.htm

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Date: Tue, 29 Sep 2009 19:28:02 -0500
From: "John E. Malmberg" <wb8tyw at qsl.net>

I am trying to set up a workshop where I may be able to play with my 
COCOs and other toys again, so this is not totally off topic.

Unfortunately the builder of my house, while putting in the plumbing for 
downstairs bathroom, only put one spare power cable, a 12 AWG with 3 
insulted wires and a ground.  That would be good for 2 20 A split 
neutral circuits.

This is in addition to the required single 20 A circuit in the basement 
that is currently active.  Combined that gives me a total of 60 A in the 
  basement.

The resulting 60 Amps is more than sufficient for powering the expected 
TVs, Ham Radios, and computers, and workbench tools.

I would prefer though to have a sub-panel with multiple circuits, where 
each circuit would just be 15 A, for the computers and the Ham Radios 
and TVs.

I have not been able to find a strong reference as to if this would pass 
   a housing inspection.

All the references on the Internet I have seen is using 30A dual 
breakers and 10 AWG feeders to a sub panel.  Putting in the 10 AWG 
feeder would be difficult as there is no good path from the main panel 
in the garage to the basement.  I would likely have to run visible 
conduit on the outside of the dry-wall.  As such, I would probably have 
to get a professional to install that.

The NEC does seem to have tables indicating that a 20 A feed is allowed, 
as long as 20 A ganged breakers are used to protect it.



-- 
Frank Swygert
Publisher, "American Motors Cars" 
Magazine (AMC)
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