240v Air compressor disconnect with 120v switch

[bondsman]

Is this safe or not???

Like my lift and the compressor itself. One of the hot wires going into the motor is run through the upper limit (on the lift) and the pressure switch (on the compressor). When those trip and break the connection, the motor stops.

Now, could I just drop the run by the door and put one of the hot wires on a switch to kill the compressor? Or should I just get a disconnect for it?

 

[Charles (in GA)]

Interrupting one side of the 240v will stop the motor, but it isn't safe. Install a disconnect that interrupts both hots (L1 and L2) to the compressor.

Charles

 

[2LTim]

Bondsman:
Unless your compressor has a "Contactor" (a magnetic relay type device) that actually starts the motor, it would not be considered a "Safe" thing to do using a conventional 110 volt single pole switch to control it. If you have a compressor that draws less than 20 amps, you can run both of the 220 wires through a switch box and install a DPST (Double Pole, Single Throw) switch to kill both legs of the 220. This is acceptable and common practice. DPST switches are available at most big box stores. They are not available in contractor packs that I have seen. And they will usually run you in the neighborhood of $20 to $30.
The reason you do not want to use a 110 switch is this; If you turn the switch off on only one leg of the 220, your compressor will not run, but you may be lulled into a false sense of security in tinkering with the circuit while the entire thing is live with a minimum of 110 volts!! When the comp if not running due to the open switch, it is just a conductor in the circuit, which carries the unswitched 110 line all the way back to the "Load" side of the switch. You will essentially have 220 volts of potential available across your switch in the "Off" position, NOT COOL!!
Hope this helps!
Good luck,
Tim

 

[trythis]

Right now how do you turn it off and on?

 

[bondsman]

There is a contactor with the compressor. The motor draws 25.5 amps. Now that I think of it, I could just tap into the wire from the pressure switch that runs back to the contactor and put a switch. It would be like manually tripping the pressure switch. Does that make sense?
Right now, I don't have the compressor installed. I just picked it up at an estate auction. I am in the process of running the wire, but was planning on using the breaker to turn it off. I don't like the idea of using the breaker to turn it off.

 

[hillbilly1]

There is a contactor with the compressor. The motor draws 25.5 amps. Now that I think of it, I could just tap into the wire from the pressure switch that runs back to the contactor and put a switch. It would be like manually tripping the pressure switch. Does that make sense?
Right now, I don't have the compressor installed. I just picked it up at an estate auction. I am in the process of running the wire, but was planning on using the breaker to turn it off. I don't like the idea of using the breaker to turn it off.

Yes, since it has a starter, just break the pressure switch wire with your switch. You will still need a disconnect, unless it's within sight of the panel. Breakers unless marked "SWD" are not designed to be used as a switch to turn the compressor off and on.

 

[bondsman]

How is this for an idea? Just checked home depot site and there is a double pole 30 amp switch for motors and equipment, could I tap into one of the wires from the switch to the starter and install a light that would indicate whether our not there is power running to the compressor? A visual reminder to turn it of...

 

[Charles (in GA)]

How is this for an idea? Just checked home depot site and there is a double pole 30 amp switch for motors and equipment, could I tap into one of the wires from the switch to the starter and install a light that would indicate whether our not there is power running to the compressor? A visual reminder to turn it of...

So long as its motor rated for the horsepower you intend to run on it, this would serve as a disconnect. As far as running a warning light when its on, you also need a neutral (which you probably do not have on this circuit) or a 240v bulb (which is probably expensive when you do find it)

Tapping into the pressure switch circuit that controls the starter is OK so long as you do not switch it off while it is running. MOST compressors use the pressure switch to operate a valve to dump the head pressure after the pressure switch shuts off the compressor. If you interrupt the circuit while it is running, this won't happen and the next startup will be against head pressure and will trip the breaker.

If you happen to have a compressor with a centrifugal or oil pressure operated head unloader, then this will work just fine with no problems

Charles