Air compress 240v question

[dcf1999]

I've searched everywhere and cannot fine a good answer. I just bought a 80 gallon 240v compressor and now I'm Running the electrical. I installed a 30 amp double pole breaker with 10 gauge wire to the outlet.

My question is with making the "power cord" for the compressor. Since I ran 10 gauge wire on the 30 amp breaker, I would assume I would use 10/3 SJOOW wire. The motor's plate says the amp rating is 22 amps. However when looking at the factory wiring between the motor and the pressure switch (I guess that would be considered the motor's power cord) it's 12 gauge wire. I would have thought for a 22 amp motor, they would have used 10 gauge. Why is it they used 12 gauge instead of 10? Because of this, can I use 12/3 SJOOW wire for the power cord? I have both 10 and 12 SJOOW gauge wire on hand and know the logical solution is to just use the 10 gauge but I guess I'm more so curious if i'm allowed to use it (the 12 gauge that is). It seems If the motor manufacturer can use 12 gauge for a power cable on their 22 amp motor, why couldn't I use it?

The receptacle on the wall and the plug are rated for 30 amps

 

[Jadnashua]

The wire's length affects its resistance. Inside of a device, the design engineer can calculate what that resistance is, how hot the wire will get based on the actual load, and can optimize the costs and performance. Anything outside of the device is out of the picture...it assumes it will have full voltage. Substituting smaller wire than it is designed for can mean less voltage, more heat, and improper operation.

Use whatever size wire they call for to supply the device to ensure it doesn't get too hot and the supply voltage is not restricted.

 

[Sponsor]

 

[DonL]

I would guess that you may have a 5 HP motor for a 80 Gal compressor, and it is 2 stage.

I would use the biggest wire in a Appliance Pigtail that will fit your outlet.

As Jim says, It is wire length that matters.

I would use at least a #10 , 6 foot pigtail, For a motor like that. That motor requires a Lot of power to get it started, and a lot when the tank gets near full.

I installed a Blower on the head of my 80 Gal, because it does get Hot when you get to 160 psi or so. The Flywheel does not cool the head enough for my liking.

Bigger wire does not hurt anything.


Good Luck on your project.

 

[dcf1999]

I did use 10 gauge because, like said above, you can't go wrong with bigger wire. I also used a twist lock type plug because i like being able to lock the plug into te socket.

I was just wondering why the motor maker decided to go with a smaller wire but I understand the reasoning now.

Thank you guys.

 

[Jadnashua]

Basically, bigger wire costs more, and when you can use a smaller one without compromising operation, the things are usually built to minimize costs. It also may require the whole chassis or internal wire passages to be larger when it isn't desired. Sometimes, they get it wrong, but to pass UL, etc. testing, it is usually correct.

 

[DonL]

30 Amp Appliance Pigtails are normally 10 Gauge.

That pressure switch should work with 10 Gauge no problem.

Using smaller wire to save cost is just plain dumb I think.

If the wire is to big for the hole, Well Don't you just drill a bigger hole ? lol


dcf1999 did Good.

 

[Jadnashua]

Using smaller wire to save cost is just plain dumb I think.

If the wire is to big for the hole, Well Don't you just drill a bigger hole ?

The comment about smaller wire was in the manufacturing of the device...not running power to the device, which is out of the design parameters...it expects code compliant supply wiring...what's inside is up to the designer. The user's manual will indicate the required supply wiring, and you can go bigger that specified, you can never go smaller.

 

[DonL]

The comment about smaller wire was in the manufacturing of the device...not running power to the device, which is out of the design parameters...it expects code compliant supply wiring...what's inside is up to the designer. The user's manual will indicate the required supply wiring, and you can go bigger that specified, you can never go smaller.

Like you said the length of the wire is what is important for Voltage Drop.

Kind of sad that the NEC does not require a bigger conductor for longer wire runs. Why is that ?

You can do better and safer than NEC requirements.


NASA taught me a bit, and experience taught me a Lot.

 

[Vegas_sparky]

NEC does require adjustments in wire size to compensate for voltage drop. You're supposed to stay within 3% of your service voltage for branch circuits, when under load.

Also, the factory conductors inside the equipment typically have a higher temperature rating than the conductors run through the building that feed them. Because of their relatively short length, and different type of insulation, they perform reliably at higher temperatures.

 

[JWelectric]

Voltage drop is not an NEC issue. The NEC only recommends a three percent and does not mandate anything concerning voltage drop.

The voltage delivered by the utility can vary more than three percent.

Look at your range if you have an electric range. It is supplied with at least a 40 amp circuit but the wiring inside is 12

 

[ActionDave]

NEC does require adjustments in wire size to compensate for voltage drop. You're supposed to stay within 3% of your service voltage for branch circuits, when under load....

That is not true, with the exception of one rule that I can think of for fire pumps, the NEC has zero requirements for VD.

I just hooked up a circuit for a lamp post 420' from a house, used 12 AWG wire, tested open circuit voltage and voltage under load, 123V and 113V respectively; do I concern myself with this at all? No. That light is going to be as happy as cat with a clean litter box.