I currently have my electric clothes dryer hooked up in my garage and it's a standard 3 prong 240v plug. I am looking to buy a 60 gallon air compressor that runs on 230v single phase and am hoping that although it wants to be hard wired I can wire up a plug and just swap out the dryer and compressor when I need to use one or the other. I'd love to wire up a dedicated run from the main breaker box but I have maxed it out already with 3 120v circuits added when I expanded the garage almost 2 years ago. Would there be a safety concern in wiring things up this way or should I get someone in to pull another feed from wherever (back of the meter?) to another circuit breaker box and then run a new line over to where I'd have the compressor set up?

8/27/2010 5:35:35 PM

What's the breaker size for the dryer?

Depending how much current the compressor draws, switching between the dryer and the air compressor shouldn't be a problem.

You might want to consider feeding a small sub panel off of your main breaker box. You just need to be careful that you aren't overloading the main box.

8/27/2010 7:01:36 PM

dryer is on it's own 30 amp 2 pole off the main box in the house. I have a run (60 amp 2 pole) going from that box down to a second box in the garage, which has 4 20 amp single pole circuits (smoke detector, garage door and overhead lights, 2 runs for wall outlets). I have no unused spots in the main box so I'm kind of at a loss in terms of what to do outside of the swapping plugs between the dryer and compressor at this point, and even if I could do some mini breakers I still don't have 30 amps to spare off the main house breakers.

Compressor is in the 15 amp range according to all details I'm seeing online. 3-4hp motor.

[Edited on August 27, 2010 at 8:09 PM. Reason : f]

8/27/2010 8:03:55 PM

You might be able to get away with using another 30/2 breaker because lots of the items on your main box aren't always on items. Most of them are receptacles or lights. Even so, the breaker size isn't indicative of the actual load on that circuit (e.g. You could have 2 duplexes on a 20/1 circuit that only pull 0.4 KVA when its full load capacity is 1.6 KVA).

Is your house using a 200A main panel? Also, how many pulls is the panel?

8/27/2010 9:57:48 PM

200 amp main, yes. 20 spots for breakers. Adding up all of the individual breakers I have 405A. I was told the wire being used for the dryer drop is at it's limit for the run/amp/voltage so there's no using it to add a junction box for the compressor.

It's an older house that is wired very oddly in the fact that some circuits are way under-utilized and others have random outlets/switches on them and are near the limit when I'm running things in the living room. Add in the fact that a couple years after the house was built they added a small storage area downstairs and borrowed off other stuff for the outlets and did that too-small-for-todays-code wiring job and when I expanded it to become a full garage I had to work around all of those problems when doing the other wiring, while also having to meet the newer building codes out here at the beach.

8/27/2010 10:40:07 PM

There's no way that breaker box is pushing 60 amps with 4 20/1 breakers. You could probably replace it with a 10 pull panel and put your 30/2 dedicated circuit on it.

Even if 20/1 breakers were "full", you would be pulling about 1.92 KVA per circuit (so 7.68 KVA total).

With an 80% safety factor, you can pull 48 amps through that 60/2 breaker. Multiply by .240 and you get 11.52 KVA total. So that would leave you with 3.84 KVA to play around with (this is all worst case scenario, too).

15 amp compressor x .240 = 3.6 KVA. That might seem like you are "pushing it", but there is no way a receptacle/light circuit is pulling 1.92 KVA for any amount of time. In all likelyhood, they are pulling 0.5 KVA or nothing at any given moment.

Personally, I think the new panel is the least invasive solution. It makes sense to replace that breaker box with the panel just because whoever put a 60/2 breaker on that box must've anticipated significantly higher power requirements on that box. Since there aren't, it saves you the trouble of having to buy a large breaker and large copper cable.


[Edited on August 28, 2010 at 2:03 PM. Reason : Residential uses 120/240, not 120/208]

8/28/2010 1:56:38 PM

Quote :

"I can wire up a plug and just swap out the dryer and compressor when I need to use one or the other."

This will be fine if you don't mind swapping plugs.

8/28/2010 5:40:28 PM