Wire Gauge for Motor Starter

[exranger06]

Back with yet another compressor wiring question - I plan on adding a starter/contactor to my compressor when I get it hooked up. I want to add a remote switch to switch the contactor on and off from the garage (compressor and starter are in another room). What gauge wire should I use for the switch? Do I have to use the same gauge wire as the motor (I'll be using 10 gauge THHN)? Since it'll have only a small amount of current to energize the coil, can it be smaller gauge? This is the starter I was going to buy: https://www.amazon.com/dp/B01MTS46KC/_encoding=UTF8?coliid=I1578QQWVCSU5&colid=38XAXG6RZ11QD

 

[Stuart in MN]

Tell us what kind of compressor you're talking about and the motor size, or at least provide a link to your previous question.

 

[exranger06]

I don't see how the compressor model is relevant to this question, but OK. The OP of this thread has the same compressor as me and I asked a bunch of questions in that thread: http://www.garagejournal.com/forum/showthread.php?t=353669

 

[donpauli2]

To put a switch and use 120 volts or 240 since you're activating only the contractor coil, 14 is sufficient but not to operate the motor itself


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[alfredeneuman]

Motor Control Conductors are addressed in NEC table 430.72(B) and the breaker (or fuse) size will control the size of the control wires if tapped directly from the circuit feeding the motor.
Since the control circuit is going to extend beyond the enclosure........

If the breaker is no larger than 45Amps you can use a #14
If no larger than 60Amps you will need a #12
Up to 90 amps a #10

Edit: Since the recommended C/B size is 50 Amps, then a #12

 

[alfredeneuman]

To put a switch and use 120 volts or 240 since you're activating only the contractor coil, 14 is sufficient but not to operate the motor itself

1 problem is that the disconnect is required to shut off ALL conductors to the motor; even the control wires and you would need a fused control transformer or if tapped off of the main conductors, a fuse in the control circuit

 

[exranger06]

The disconnect will shut off all conductors. I was going to simply wire the pressure switch and the remote toggle switch in series to the coil of the contactor. You're saying I'd need a fuse for that? I wouldn't have to do that if I was using just the pressure switch. I don't see how adding another switch changes that. I also don't see the need for a transformer?

 

[matt_i]

The electrical load due to energizing the coil is milliamps usually. Good to follow the code but something like a 100va dry transformer would probably work if you ran a 120vac control voltage. And that's good for ~1 amp....

 

[exranger06]

I'm having a hard time understanding why I need a transformer. If I didn't have the remote switch, I'd just have the pressure switch wired directly to the coil without any transformer. All I'm doing is adding a second switch in series with the pressure switch. Why can't I just do that?

Is the transformer to bring the voltage to the coil down (the coil is rated for 240V so that's probably not it), or is it so the wiring to the remote switch is low voltage? (I'm guessing that's it) I'm already running high voltage to the compressor, so one more set of high voltage wires isn't a big deal.

 

[1500hd]

You are correct, just need to wire a switch in series with the pressure switch. Most starters have L2 jumpered to A2 of the coil. Switch the L1 line from pressure switch with #14 wire.

 

[alfredeneuman]

You don't need a fuse OR a transformer. That was in response to donpauli2's post (#4)
All you need is #12 (NOT #14)to the remote switch since the suggested breaker size is 50Amp
Reread post#5.
It's in the NEC

 

[exranger06]

I'm actually using a 40 amp breaker per wyliesdiesels recommendation in the other thread. I suppose I can run 12 gauge anyway in case I need to upsize the breaker to 50 amps.

Most of my wiring will be in conduit, but there is a section where I will have 8/2 Romex spliced to the #10 THHN to power the compressor. I assume 12/2 Romex spliced to #12 THHN is fine for the control wiring?

 

[alfredeneuman]

12/2 NM would be fine for the control wiring as long as it is protected from physical damage.
...but Quincy recommends a 50 Amp breaker in their specs!

 

[wyliesdiesels]

You don't need a fuse OR a transformer. That was in response to donpauli2's post (#4)
All you need is #12 (NOT #14)to the remote switch since the suggested breaker size is 50Amp
Reread post#5.
It's in the NEC

I'm actually using a 40 amp breaker per wyliesdiesels recommendation in the other thread. I suppose I can run 12 gauge anyway in case I need to upsize the breaker to 50 amps.

Most of my wiring will be in conduit, but there is a section where I will have 8/2 Romex spliced to the #10 THHN to power the compressor. I assume 12/2 Romex spliced to #12 THHN is fine for the control wiring?

12/2 NM would be fine for the control wiring as long as it is protected from physical damage.
...but Quincy recommends a 50 Amp breaker in their specs!

Where do you see 50a recommended by quincy?

The only time i see that is on the distributors site.

I searched quincy's manuals and couldnt find a recommended breaker...

 

[matt_i]

I'm having a hard time understanding why I need a transformer.

You don't. My example of a 100va transformer was to show how low the current requirement would be.

If you do use a "wall switch" I would carefully label it inside and out, that it switches 240vac. Someone in the future will greatly appreciate that.

 

[alfredeneuman]

Where do you see 50a recommended by quincy?

The only time i see that is on the distributors site.

I searched quincy's manuals and couldnt find a recommended breaker...

It IS on the distributor's site under SPECS
aircompressorsdirect.com/Quincy-2V41C60VC-Air-Compressor/p855.html?gclid=CLSsqs3NndICFRNWDQod3t4J3A

Do you suppose it's the wrong info and the info that YOU gave was correct?

 

[wyliesdiesels]

You don't. My example of a 100va transformer was to show how low the current requirement would be.

If you do use a "wall switch" I would carefully label it inside and out, that it switches 240vac. Someone in the future will greatly appreciate that.

You really dont need to switch both sides of the coil. One side is sufficient.

It IS on the distributor's site under SPECS
aircompressorsdirect.com/Quincy-2V41C60VC-Air-Compressor/p855.html?gclid=CLSsqs3NndICFRNWDQod3t4J3A

Do you suppose it's the wrong info and the info that YOU gave was correct?

I was only pointing out how the manufacturer doesnt list this in any manual that i read available on their site. I was hoping to find it somewhere...