Compressor Electrical Wiring

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Old 06-23-19, 05:04 PM
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Compressor Electrical Wiring

Hi all, I have a Campbell Hausfeld 60 gallon, 5 HP, 230 volt, 15 amp air compressor, and the wiring diagram on the electric motor (see attached photo) shows two methods of wiring (115v or 230v).

I'm going to hard wire it to a junction box with an on/off switch. My question is which method should I use (115v or 230v)?

The electrical circuit that the compressor will be tied into at the very end, has a 30 amp breaker with white romex. In fact, the entire house uses white romex, which is a little troubling to me because in my mind yellow would be the minimum for the house, and orange or black would be the most appropriate minimum for a garage where you would likely have many lights and power tools, etc..

Anyway, I'd like to know which method of wiring would be best for the compressor to work most effeciently, and how my electric bill be affected by each method (in other words, would wiring the compressor up using 230v be best for the compressor but higher electric bill, or would both be noticeably identical)?

Thanks
 
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Old 06-23-19, 05:43 PM
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You can not rely on the colour of the NM cable to indicate the gauge. It used to all be white. Check the actual cable gauge. Either measure it or check the cable casing. It will be stamped on it.

Voltage does not affect the power used. It does affect the amp draw allowing smaller gauge cable to be used at 240 volts.
 
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Old 06-23-19, 07:21 PM
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I wondered about the white cable, so I will check for stamping. The house was built (and wired) in the 80's.

I sort of comprehend your comment regarding voltage allowing amp draws through smaller gauge wire, but can you please elaborate further as to how it can be used advantageously in my situation?
 
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Old 06-23-19, 07:25 PM
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The motor is rated for 24 amp at 120 volts. That would require a 30 amp breaker and #10 cable.
At 240 volts it draws 12 amps which could be done with #14 cable. So If your existing cable is less than #10 you could run the compressor at 240 without changing the cable.
Lower amps draw also results in lower voltage drop. If the run is long that could be a significant issue.
 
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Old 06-23-19, 07:38 PM
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Exactly what all does the electrical wiring now in place serve? Normally with a 30 ampere circuit breaker this would need to be a #10 cable BUT under some circumstances it could be a smaller gauge (larger number) IF it supplied a device or appliance with an electric motor.

For a non-heating appliance the general rule of thumb is that doubling the voltage from 120 to 240 will halve the required amperage; reducing the amperage reduces the necessary size of the wiring to avoid voltage drop issues.

If that is the motor nameplate on the proposed air compressor note well that it is NOT a "5 horsepower" compressor. Air compressors, especially for home-shop usage are notoriously given ludicrously high "horsepower" ratings. I know of no reason for this other than advertising.

Notice on that nameplate the motor will draw a full-load amperage of 24 at 115 volts while only drawing 12 amperes at 230 volts. At 120 volts you would need #10 conductors to adequately supply enough electricity to properly operate this motor whereas at 240 volts it could be done using #14 conductors.
 
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Old 06-24-19, 05:30 AM
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For motor wiring you use the HP off the motor data plate and use the NEC table 430.248 for amps X 125% to size the conductors. It so happens the data plate amp agrees with the NEC table, sometimes they don't.
 
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Old 06-24-19, 02:10 PM
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That's great information, thanks!

The cable is marked "12-2 with ground".

The garage has two circuits, let's call them front and back.

The front is on a 20A breaker, and has 4 outlets, feeding 2 garage door openers, a video doorbell and a wi-fi range extender.

The back is on a 30A breaker, and has 8 outlets, a porch light, 2 shop lights and a small Wyze USB video camera.

The compressor would reside at the very end of either run, and there would be over 30' of cable between the box and the compressor. The front circuit is the shorter of the 2.

It sounds to me like I'd be better off (and perhaps necessary) to wire the compressor with 230V. If so, am I correct that i'd need to switch one of the breakers from a 120V to a 230V? Also, I can't run any outlets or other items which are not 230V on that same circuit?

Assuming that my statement above is correct, I'd love to simply run a new 230V line straight from the breaker box to the compressor with a new 30A breaker, BUT my breaker box looks completely full.
 

Last edited by Turpy; 06-24-19 at 02:17 PM. Reason: Additional details
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Old 06-24-19, 03:01 PM
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The back is on a 30A breaker, and has 8 outlets, a porch light, 2 shop lights and a small Wyze USB video camera.
This would be a mistake or an error in wiring. A standard receptacle circuit cannot be protected over 20A.

Running that compressor on 240v would be a smart choice. That means you will need an additional circuit just for the compressor.
 
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Old 06-24-19, 03:11 PM
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Then a new separate line it will be.

Should I also replace the 30 amp breaker with a 20 for the back circuit?
 
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Old 06-24-19, 03:33 PM
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Yes replace the 30A breaker with a 20A breaker if the wire is #12.
 
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Old 06-24-19, 04:52 PM
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Nothing in the breaker box is labeled, and when we bought the house we shut them off one by one and made a list. There were 3 breakers that we couldn't find what they fed, two of which were doubles. Today I noticed what looks like a 230v clothes dryer receptacle (see attached) fed by a single line coming out of the side of the breaker box, and sure enough one of the double breakers controls it (I'm guessing that it's the only thing on that circuit). Looks like perhaps they had a clothes dryer in the garage as well as the one in the laundry room which is on it's own circuit which I already tested.

The double breaker controlling it says 50 on each and they're hooked together (attached). The other good news is that the same white cable that feeds this receptacle is only about 8' long, so I could just run new romex from the breaker up through the rafters and down the stud nest to the compressor. I've got a a 250' roll of yellow 12/2, unless I need to use 10/2 instead.

The only other question is should I leave the double 50A breaker (would this be 100A total), or replace it with 2 separate 20A or 30A leaving me with an extra?
 
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Old 06-25-19, 05:20 AM
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To wire that compressor on 240V, you would want to change out the breaker for a 2-pole 20A breaker and use 12-2 cable. Eaton makes exact replacements for Westinghouse/Bryant breakers so you should have no trouble finding one - BR220.

At the compressor motor make sure to follow the "High Voltage" diagram for where to connect the incoming hot lines L1 and L2; and the motor terminal T2 and T3.
 
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Old 06-25-19, 08:45 PM
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A two po!e breaker trips at whatever the panel says, not what both handles.add up to.
 
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Old 06-26-19, 06:42 PM
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Ok, I found and bought the Eaton BR220. I've read about the difference between single-pole & double-pole, and I think that in order to provide 240V I need the double (hence your recommending the BR220 rather than the BD220).

One remaining question, aside from simply connecting the 12/2 wire(s) to the new breaker exactly like the existing one (assuming that the person who originally wired it knew how and did so correctly), how do I connect the 12/2 wire to the BR220 breaker? 12/2 wire has 3 wires right? White, Black and Bare/Ground.

Thank you all for your generous advice and helping me get this done right (and SAFE!). I can't put a price on that!!
 

Last edited by Turpy; 06-26-19 at 06:46 PM. Reason: missplellings
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Old 06-26-19, 06:47 PM
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White and black connect to the breaker and ground connects to the ground bar.
 
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Old 06-26-19, 06:47 PM
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Yes.... it's 12/2 w/ground. The white and black wires connect to the 2P breaker.
The ground goes in the ground bus bar in the panel.
 
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Old 07-06-19, 04:02 PM
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Almost done

Ok, I've got the new breaker installed and the wire ran to the light switch in the junction box. I "think" that I understand how the compressor is and needs to be wired, but I'd really appreciate you all's expert confirmation or correction!

Again, this is the motor wiring diagram:
https://www.doityourself.com/forum/a...1&d=1562453396

Here's how I think it should be:
https://www.doityourself.com/forum/a...1&d=1562453983

Here's the solenoid that controls the motor:
https://www.doityourself.com/forum/a...1&d=1562453749

Do I simply wire up the new supply line the exact same as the existing plug in cord?

Thanks
 
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