Guidance on electrical wiring for new air compressor requested

16259 Views 14 Replies 9 Participants Last post by emtnut, Feb 10, 2016

damiencurrier

Discussion Starter · Feb 8, 2016

Hello,

New member here. I recently purchased a Porter Cable 60-gallon stationary air compressor (PXCMLC3706056) for use in my garage. The primary function will be to drive a rivet gun (and various other aircraft building tools) during my RV8 build project. I was given some advice by another RV8 builder to purchase a dryer cord and run the compressor from the same outlet my clothes dryer runs from since that's already wired for 240V. (The compressor is 230V / 15 AMP, according to the serial plate).

However, I think I would like to run a new line from my home panel in conduit to the garage so that I can also add a disconnect switch in the garage next to the compressor for safety. I don't know "a lot" about electrical wiring, but I would say I know enough to be dangerous?
My questions are:
1) What kind of breakers do I need to add to my panel?
2) What kind of wire to I need to buy? I'm guessing [email protected] 14-guage wires?
3) Do I only need 2 wires? There are only 2 terminals inside the pressure switch to wire to, so I think there is no ground required?
4) What kind of disconnect box should I get?
5) Depending on the size of the wire, is 1/2" conduit sufficient? The conduit will be run along the outside of the house attached near the bottom of the wall with straps screwed into stucco. I measured and the route I plan to take is 45 feet.

Thanks, in advance.

1 - 15 of 15 Posts

joed

· #2 · Feb 8, 2016

1. A double pole 15 amp breaker that matches your panel.
2. 14/2 cable will be fine you don't need a neutral so the white can recoloured to black.
3. Yes only two wires are needed plus ground.
4. Does the compressor have a plug? That is all you need.
5. 1/2" will be fine for #14. You will want THWN wire not cable in the conduit. Get enough black for both runs or a red and black. You can't use white in this case.

brric

· #3 · Feb 8, 2016

You will need three conductors to the disconnect unless you are using metallic conduit from the house panel to the disconnect.
Two-pole 15 amp circuit breaker. two black, one green 14 guage THHN/THWN conductors. Two pole 30 amp disconnect, fused or unfused.
I am relatively sure there is a grounding location on the pressure switch.
Liquid-tite or MC cable from the disco to the pressure switch.

dmxtothemax

· #4 · Feb 8, 2016

Is the compressor the only thing you want to run in there ?
I would consider using larger wire and running 4 wires,
2 x hots, 1 x neutral & 1 x earth.
That way you can add at a later date without
having to change/re-run your main feed.
Future proofing so to speak.

Reactions: 1

al_smelter

· #5 · Feb 8, 2016

dmxtothemax said:
Is the compressor the only thing you want to run in there ?
I would consider using larger wire and running 4 wires,
2 x hots, 1 x neutral & 1 x earth.
That way you can add at a later date without
having to change/re-run your main feed.
Future proofing so to speak.

The best advice is above:

But if not for the future, I would at least keep it off the edge. A 15 amp name plate, #14 wire, and 15 amp breaker is asking for trouble. It will cost very little more to do it right. I would upsize at the very least to #12 wire. I would also up size the OCPD to counter the locked rotor starting current. If you use, say, #12, you could upsize to at least a 30 amp OCPD. At 15 amps (sounds like you have 2-3 HP) FLA name plate, starting the compressor with a 15 amp OCPD could give nuisance trips.

I ended up installing an automatic drain valve on my big upright, and I have a small 240 volt air dryer as well. The neutral came in pretty handy for the drain valve.

Reactions: 1

joed

· #6 · Feb 9, 2016

If it's a 15 amp name plate then a 15 amp circuit is probably too small. I thought you meant the unit required a 15 amp circuit. What does install directions say for circuit size?

Reactions: 1

MrElectricianTV

· #7 · Feb 9, 2016

damiencurrier said:
Hello,

New member here. I recently purchased a Porter Cable 60-gallon stationary air compressor (PXCMLC3706056) for use in my garage. The primary function will be to drive a rivet gun (and various other aircraft building tools) during my RV8 build project. I was given some advice by another RV8 builder to purchase a dryer cord and run the compressor from the same outlet my clothes dryer runs from since that's already wired for 240V. (The compressor is 230V / 15 AMP, according to the serial plate).

However, I think I would like to run a new line from my home panel in conduit to the garage so that I can also add a disconnect switch in the garage next to the compressor for safety. I don't know "a lot" about electrical wiring, but I would say I know enough to be dangerous?
My questions are:
1) What kind of breakers do I need to add to my panel?
2) What kind of wire to I need to buy? I'm guessing [email protected] 14-guage wires?
3) Do I only need 2 wires? There are only 2 terminals inside the pressure switch to wire to, so I think there is no ground required?
4) What kind of disconnect box should I get?
5) Depending on the size of the wire, is 1/2" conduit sufficient? The conduit will be run along the outside of the house attached near the bottom of the wall with straps screwed into stucco. I measured and the route I plan to take is 45 feet.

Thanks, in advance.

How many horsepower is the motor on the compressor?

damiencurrier

Discussion Starter · #8 · Feb 9, 2016

dmxtothemax said:
Is the compressor the only thing you want to run in there ?
I would consider using larger wire and running 4 wires,
2 x hots, 1 x neutral & 1 x earth.
That way you can add at a later date without
having to change/re-run your main feed.
Future proofing so to speak.

Yes, the air compressor is the only thing I want to run there. It needs a dedicated circuit. There are other normal outlets in the garage i can use for smaller / non-pneumatic tools.

damiencurrier

Discussion Starter · #9 · Feb 9, 2016

MrElectricianTV said:
How many horsepower is the motor on the compressor?

The motor is rated at 3.7 HP

damiencurrier

Discussion Starter · #10 · Feb 9, 2016

joed said:
If it's a 15 amp name plate then a 15 amp circuit is probably too small. I thought you meant the unit required a 15 amp circuit. What does install directions say for circuit size?

I am also worried the 15 amp is too small... the instructions dont give much guidance other than "ask a licensed electrician".

It does say the motor will draw several times the rated amount when it first starts up and recommends a time-delay fuse if fuses are used. Not sure the difference between a fuse and a breaker beyond a fuse being a one-time burn out thing and a breaker being reuseable after it is tripped...

Any suggestion on sizing the circuit? The compressor is 230V, 15 amp, single phase rated with a 3.7 HP motor. The wire distance from the unit to the panel is roughly 45 feet.

MrElectricianTV

· #11 · Feb 9, 2016

damiencurrier said:
I am also worried the 15 amp is too small... the instructions dont give much guidance other than "ask a licensed electrician". It does say the motor will draw several times the rated amount when it first starts up and recommends a time-delay fuse if fuses are used. Not sure the difference between a fuse and a breaker beyond a fuse being a one-time burn out thing and a breaker being reuseable after it is tripped...

Any suggestion on sizing the circuit? The compressor is 230V, 15 amp, single phase rated with a 3.7 HP motor. The wire distance from the unit to the panel is roughly 45 feet.

At least #12 wire should be used, but I think a #10 would be better considering the starting load. A circuit breaker has a built-in time delay. You might want to install a manual motor starter to protect the motor from overload.

Oso954

· #12 · Feb 9, 2016

the instructions dont give much guidance other than "ask a licensed electrician"

No, what the instructions say is:

"Ensure that all wiring is done by a licensed electrician, in accordance with the National Electrical Code.. "

micromind

· #13 · Feb 10, 2016 (Edited)

Code requires a minimum #12 wire and a maximum 45 amp breaker for a 3HP single phase motor operating on 230 volts.

If it were mine, I'd use #10 and a 30 amp breaker. If it trips on starting, go with a 40 and keep the #10s.

The reason for using #10 is because it is a 3.7HP motor. #12 may very well be compliant, I'm too tired and lazy to figure it exactly.

Lol.

Rob

al_smelter

· #14 · Feb 10, 2016

If your nameplate FLA is actually 15 amps, you must have one of those creative "peak" horsepower rated motors. A single phase 2 Hp is rated @12 amps; 3Hp is rated @17 amps (@230 VAC). It is unlikely to be almost 4 true horsepower.

Read post #5 and #13 again. And I still maintain that a neutral will come in handy someday, especially after you have to lay on the floor to drain the tank multiple times (you WILL drain the water out won't you?).

http://www.amazon.com/iiMash®-AC110...id=1455073076&sr=1-3&keywords=automatic+drain

Just an example.

Reactions: 1

emtnut

· #15 · Feb 10, 2016

damiencurrier said:
Hello,

I think I would like to run a new line from my home panel in conduit to the garage so that I can also add a disconnect switch in the garage next to the compressor for safety. I don't know "a lot" about electrical wiring, but I would say I know enough to be dangerous?
My questions are:
1) What kind of breakers do I need to add to my panel?
2) What kind of wire to I need to buy? I'm guessing [email protected] 14-guage wires?
3) Do I only need 2 wires? There are only 2 terminals inside the pressure switch to wire to, so I think there is no ground required?
4) What kind of disconnect box should I get?
5) Depending on the size of the wire, is 1/2" conduit sufficient?
Thanks, in advance.

I installed the same setup (Dewalt, but same compressor)for a guys home garage.
Calculations came up as
20A ocpd , #12 wire
Home depot has a cheap disconnect, about $25. 30A. Use 30A slow blow fuses.

1 - 15 of 15 Posts

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