How to add a 240V line for an air compressor.

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Old 06-21-05, 03:44 PM
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How to add a 240V line for an air compressor.

Iím buying an air compressor needing 240V that I will put in the basement. There is no other appliance in the basement that uses 240V except I found a junction box near the furnace that runs outside to the A/C unit which I assume is a 240V line. Since running a new circuit for the compressor from the breaker box is out of the question, can I just tap into that junction box for the compressor? I guess I would have to check the specs on all items involved such as the amps rating for the compressor, A/C unit and circuit breaker etc. but even if the compressor would add too much of a load to the circuit, I could always make sure the A/C was off whenever I plan to use the compressor. Any suggestions?
 
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Old 06-21-05, 04:04 PM
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Originally Posted by atikovi
Since running a new circuit for the compressor from the breaker box is out of the question, can I just tap into that junction box for the compressor?
No way. Running a new circuit has to be in the question. Tapping in to the A/C circuit would dangerously overload that circuit. The air conditioner is run on a special type of circuit designed for a single motor. Connecting a second motor (i.e. your new compressor) to the circuit will cause a severe overload. At best this would pop the breaker constantly. At worst, it will ruin your A/C and air compressor and catch fire.

Why is running a new circuit such a problem? There are many, many options for fishing wire through walls, popping outside with a conduit, adding a subpanel, using tandem breakers, etc.
 
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Old 06-21-05, 04:05 PM
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It is unlikely that you can safely tap into the A/C circuit. If running a new circuit is truly out of the question (which is hard to believe), then you may need a 120-volt compressor (which might need a new circuit too).
 
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Old 06-21-05, 04:28 PM
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I HAD a 120V compressor which often kept tripping the basement breaker if I had the lights on at the same time. A real PITA to drag out an extension cord from the next floor to power a floor lamp just to see what I was doing whenever I used my sandblasting cabinet. If I didnít have the lights on the compressor would run fine. Why canít I do the same for this 240V A/C line? I.E. keep the A/C off whenever I want to use the compressor. Running a new circuit would require tearing up walls and ceilings as the breaker box is on another floor on the other side of the house.
 
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Old 06-22-05, 09:20 AM
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What it sounds like is that you need a lot more power in the basement workshop than you currently have available. A workshop subpanel could be a good option; you'd only have to install the feeder wire from the main once. With the right cable route, ceiling repair could be minimal. Perhaps you could run a conduit outside the house along the foundation to the basement workshop. After a sub is installed, you could put many new circuits in for the workshop.

I'm not saying that you couldn't hook the compressor up to the A/C line and only run one at a time. That would work, but the issue is really safety. The codes are written to prevent fires and electrocution; in this case it's fire. Just because something works doesn't mean it's safe.

One more point. If you did accidentally turn both on at the same time, the voltage drop and subsequent current increase could very well be severe enough to burn out both the air compressor and air conditioner motors depending on where the OCPD devices are.
 
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