Help choosing a contactor

[ALinCarolina]

My air compressor is in the basement of my shop which has worked out well for noise, etc. When I was building the shop I had the foresight to run 14 ga wire from a switch by the front door down to the compressor site, planning on installing a contactor/relay to be able to turn the compressor off and on without going down to the basement. I'm ready to do that now but want to be sure I get the right size and type of contactor and the choices are bewildering.

The compressor is a big one. Duplex with two 7.5 hp motors supplied with 4 ga from an 80 amp breaker. Can anyone give me a model # or link to an appropriate contactor for this beast with a 120V control side? Hoping this is a reasonable thing to do.
Please ignore my previous post. Auto correct changed it to contractor which is totally different subject

 

[ddawg16]

240 VAc or 3ph 480?

The contactor size is based on HP and voltage.

Eaton and Allen Bradly are your known names. For that size, I would hesitate to use some off brand.

You will also find two different styles, NEC and IEC styles. IEC style is going to be cheaper, but you have to make sure you get the right size. NEC styles are a bit more forgiving.

How do you turn it on and off now, at the breaker or with a disconnect handle?

If you are just using a disconnect handle, I think I'd be going with a combo starter with fuses. It would have start/stop buttons, a disconnect and a way to remotely start and stop it.

 

[ALinCarolina]

Single phase 240. At this stage I rarely turn it off so it runs here and there due to the timer drains and inevitable small leaks hence why I am looking to hook up the contactor. I turn it now with the switches on the outside of the control box

 

[454ragtop]

Does it have a pressure switch to turn the "control box" on and off now? If yes, put your switch in series with one of the wires from the pressure switch.

 

[ALinCarolina]

Thanks. So the two pressure switches use 120V I assume? Also, I double checked the wiring we ran from the wall switch by the door to the basement and it is 12 ga instead of 14, not that makes a difference.

 

[ddawg16]

You already have what you need.

Put a light switch inline with the pressure switch.

If that 14g had been a 3 cond, you could have wired up as a 3-way....turn it on or off from 2 diff locations.

 

[ALinCarolina]

That all makes sense about the pressure switches and a switch in series. I was under the impression that the pressure switches would have been 240 also and my wall switch may not be rated for it. Thanks for the suggestions.

 

[RoyArms]

Thanks. So the two pressure switches use 120V I assume? Also, I double checked the wiring we ran from the wall switch by the door to the basement and it is 12 ga instead of 14, not that makes a difference.

I agree, use the existing contactors and modify the control circuitry. Post a wiring diagram if you have one and need help. Those 2 terminals on the left side look interesting as it looks like there is a jumper between them, maybe a safety circuit you could wire a switch in there. Or looks like the pressure switch is the two colored wires. Hard to tell from your picture so if you don't know what you are doing, post more info preferably a wiring diagram.

The switch you have installed already, is it just wires from the switch to the control box? Or is it connected to a 120V circuit? Do you have 2 wires (black/white?, romex?) from the switch to the basement control box?

 

[matt_i]

What the strategy here, does the 2nd motor just back up the first one if pressure continues to drop after the 1st motor is engaged, or is there a "toggle" to equalize wear? Is there a control transformer or do the controls run at 240vac?

You need to fully understand the factory wiring first. You might be able to use a simple ice cube relay if there truly is 120vac control voltage, or even 240vac for that matter. You're just going to want to inhibit the pressure switch (or anywhere in the series chain of press sw...coil...overload) and not the incoming power....but to figure out a rock solid solution you're going to need a diagram.

 

[ddawg16]

That Eaton Easy512 is actually a programmable relay. It almost looks like a rebranded AB PicoRelay. I don't see a neut or 24 Vdc power supply, so I'm assuming the pressure switch has 240Vac going through it. For a relay, this is no issue. The Eaton module will work off 120 or 240Vac.

If you don't mind running 240Vac up to a light switch (make sure it's rated for 240 Vac), then a switch will work. If you want to keep it to 120, then install a 120Vac relay in the box. The coil is wired to your light switch and the pressure switch across the NO contacts.

That Eaton module is using low current inputs so you don't have to worry about current loads.

 

[ALinCarolina]

I'll go through my paperwork tomorrow and find a wiring diagram if possible. I took the cover off one of the pressure switches and got 122V from one side to ground. Plus there are only two wires in each switch (single pole I think it is called) so must be 120

The control box alternates between the two motors on startup and if the pressure is extra low it will also then start the second motor so both run at the same time if needed.