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Geode · Nov 25, 2007, 09:06 AM

I am planning to add a 220V band saw to my shop (requires 20A circuit), but do not have appropriate circuit in shop. However, in my garage which is adjacent to shop, I have a 220V, 20A outlet for an air compressor. As the outlet is in the common wall between garage and shop, is there any way of rewiring the existing circuit such that it could run through some kind of switch to either an outlet on the shop side or or an outlet on the garage side? The switch (if exists) would guarantee that both outlets could not be used at the same time. Is this crazy? Or should I just buy a new air compressor that runs on 110V, and plug it in elsewhere?

Thank you.

Stratmando · Nov 25, 2007, 09:17 AM

You could use a double pole double throw switch, common(center terminals)would be where you hook up the 2 hots, one side of switch to compressor, other side of switch would go to band saw.
If you have room in panel and wires not difficult to run, may take as much time, this solution, However you could use both at anytime. You may save a lot of running around if on second circuit.

Geode · Nov 25, 2007, 11:55 AM

Originally Posted by Stratmando

You could use a double pole double throw switch, common(center terminals)would be where you hook up the 2 hots, one side of switch to compressor, other side of switch would go to band saw.
If you have room in panel and wires not difficult to run, may take as much time, this solution, However you could use both at anytime. You may save a lot of running around if on second circuit.

I am not terribly familiar with working with 220 (or much other electrical, quite frankly), so please bear with me. Does what you are suggesting first imply that this switch would be located at my main panel? If that is so, I agree with you that I would be doing a lot of running around, and that I was not contemplating doing. I was wondering about a switch of some type near the present outlet end of the circuit (at the shop/garage area). Also, it would be rather difficult for me to run a second line from the panel.

Stratmando · Nov 25, 2007, 06:54 PM

You could have a 220 receptacle and doublepole doublethrow switch in first box, then run from that box to second. That would only have a receptacle.
Then the switch would have 2 hots going to center of the switch. Then top 2 screws go to 2 conductors for the first 220. The bottom 2 poles of switch would go over to second receptacle. Remember to run ground with it.

labman · Nov 25, 2007, 07:30 PM

I don't know you need the switch. Just make sure the air compressor isn't going to kick on when you are using the saw.

Geode · Nov 25, 2007, 08:30 PM

Thank you Stratmando & labman. I will cogitate on your suggestions over a beer tomorrow and consider where I go from there. Stratmando, is there a readily available switch that you are talking about... is it essentially the kind of switch you would use when setting up an alternate power source such as an emergency generator?

Geode

labman · Nov 25, 2007, 09:43 PM

They tend to be heavier duty than you need and expensive. You should be able to find one rated for 240 and 20 amps meant for lighting. Watch, it may not be rated for inductive loads such as a motor.

The beer sounds like a good plan.

Cobraguy · Nov 26, 2007, 05:59 AM

Actually, I can't think of a problem with just installing a 220V plug in your shop opposite of the plug in your garage. Just splice into the existing box (box fill requirements allowing) and install the new plug. Worst case scenario is you would have to switch the compressor off when you're running the saw. If you have 12/2 or larger on a 20A breaker, the circuit is properly protected. This should be no different than having several receptacles in your house on one circuit. We all know you couldn't plug a bunch of hair dryers into one circuit without it tripping. Install the plug and be done with it.

By the way, you may have to have that circuit GFCI protected. I'm in a dispute right now with my AHJ over two 220V circuits in my garage. They want GFCI breakers installed. I'm not sure they're necessary in my application... but they are the final word in the matter.

Geode · Nov 26, 2007, 08:25 AM

With the last two replies, I think I'm convinced to just put the additional outlet in. Costs, availability; and, yes, the saw motor is inductive type (thanks for that tip, labman) weigh in against the switch idea. Cobraguy, your logical argument cements the it... good common sense makes the best case here. I was, perhaps, being overly cautious.

Geode

labman · Nov 26, 2007, 08:44 AM

Fortunately, at least for the time being, I am under the local AHJ's radar. I have one 20 amp, 120 volt circuit with 16 outlets. 8 of them are directly over my work bench. While at times, I may have a half dozen tools plugged in, I am seldom using more than one and the 80 watt shop light. In the next month, I will be plugging in the Christmas light into it. I am conservative enough they may only run about 100 watts. The circuit is wired up with #10.

KISS · Nov 26, 2007, 11:25 AM

Another way, which is complex, but might be worth considering. You can use the bandsaw power (after the switch) to activate a contactor that would turn off the air compressor.

So, if the bandsaw was on the air compressor would turn off.

If you wanted to up the complexity even more, a delay on break timer could delay the transfer of power back to the compressor.

What you would need is a small enclosure containing a DPDT contactor mounted near the air compressor. Power to the compressor would be interrupted by the contactor when the coil is energized. You would nned a small fuse for the relay control circuit.

A cable from the bandsaw to the contactor connected after the switch. If you wanted to use a low voltage control line, then use a 220 to 24 V step down transformer.

If it was too difficult to tap into the bandsaw after the switch, then a current sensor could be used.

They are all ideas and they could be pricey.

Heck, you can even make it simpler. Do the contactor approach and just mount a swich near the bandsaw, so you can disable the air compressor while using the bandsaw.

tkrussell · Nov 26, 2007, 05:07 PM

My vote is for the Center Off Double Pole-Double Throw Maintained Switch, if possible.

One Box, one plate, one switch, three cables into box, three connectors, 6- terminal connections... done

See the attached page for a 30 amp unit rated for 240 volts 2 HP, inductive.

Or a resistive continuous load of 24 amps at 240 volts.

Worth checking the nameplate ratings of the motors.

If the motors are larger, then a simple two contactor system with interlock contacts is doable.