Wiring a compressor

[akpolaris]

I have a new Dewalt compressor that has a 3.5 hp motor and draws 17 amps. It is 220 volts. I believe it needs to be wired into a 2 pole 20 amp breaker. Can I use 12/2 to feed it? The connections show 2 hot wires feeding the motor and there are 2 screws on the plate with ground emblems indicated at each. Do I use 2 hots and a neutral to the plate? This would eliminate the ground from the wiring to the compressor. Then a 20 amp wall plug could function as the disconnect? The owners manual was very vague just directing an electrician do the wiring.

 

[k-os]

Another piece of information people will need to know to answer your question is how long of a run it will be from your breaker to your compressor.

 

[Norcal]

17.5A means 12 AWG is not going to work.

 

[pattenp]

I suggest you wire up a 30A circuit to a A/C disconnect and hardwire the comp to the disconnect. The comp needs 2 hots and a ground. A neutral is not needed.

Such as ....
View media item 16457

 

[akpolaris]

Got it. I figured it would be 30 amp breaker, #10 wire and a disconnect switch. I planned a sub panel where the compressor is going and to run this 1 circuit would be $$ and work that would be torn out when the sub panel goes in later. Guess it is best to temporarily relocate the unit until I am ready for the sub panel

 

[pattenp]

If the sub-panel is going to be close to the comp you can forgo the disconnect switch. Hardwire the comp using a junction box with a cover plate that has a knockout.

 

[wyliesdiesels]

Did this unit come with a cord and plug?

Wiring for motors is sized at 125% of NEC table FLC.

 

[akpolaris]

the unit did not come with any wires or plug

 

[md21722]

The NEC does not have a FLC amperage rating for motors that have SPL listed in the HP box of on the motor data plate. I suspect 3.5 HP is on a label on the compressor somewhere.

Figuring continuous load, 17A x 125% = 21.25A which is suitable for 12/2 wire per the NEC tables that say 12 gauge is good for 25A.

I do think that most folks just use 10 gauge for this application though...

 

[pattenp]

The NEC does not have a FLC amperage rating for motors that have SPL listed in the HP box of on the motor data plate. I suspect 3.5 HP is on a label on the compressor somewhere.

Figuring continuous load, 17A x 125% = 21.25A which is suitable for 12/2 wire per the NEC tables that say 12 gauge is good for 25A.

I do think that most folks just use 10 gauge for this application though...

You need to be clear in what you say. The designation 12/2 is a NM-b identifier and 12/2 NM-b is good to 20A not 25A. #12 THHN is good to 25A. The reason is NM-b is sized by 60deg C whereas THHN is 75deg C.

 

[akpolaris]

I will probably just get a dryer cord and use it

 

[pattenp]

I will probably just get a dryer cord and use it

I hope that was a joke.

 

[wyliesdiesels]

The NEC does not have a FLC amperage rating for motors that have SPL listed in the HP box of on the motor data plate. I suspect 3.5 HP is on a label on the compressor somewhere.

Figuring continuous load, 17A x 125% = 21.25A which is suitable for 12/2 wire per the NEC tables that say 12 gauge is good for 25A.

I do think that most folks just use 10 gauge for this application though...

When that happens, u look at the FLA on the motor nameplate and then correspond that to the NEC FLC tables to figure out what the HP is closest to. 3HP motor has an FLC of 17a.

 

[Norcal]

The NEC does not have a FLC amperage rating for motors that have SPL listed in the HP box of on the motor data plate. I suspect 3.5 HP is on a label on the compressor somewhere.

Figuring continuous load, 17A x 125% = 21.25A which is suitable for 12/2 wire per the NEC tables that say 12 gauge is good for 25A.

I do think that most folks just use 10 gauge for this application though...

12/2 wire would be NM cable "Romex®" and the NEC specifies that the ampacity be sized in the 60° column which limits 12 AWG NM cable to 20A. See 334.80

 

[akpolaris]

I hope that was a joke.

It was. Sometimes I get completely lost with the Code discussion. I can barely find an answer at times.

 

[RacerRick]

I just did a similar compressor - 3.8hp motor on it, on a pretty long run of about 80 feet from the panel.

I used 10/2 AC90 to a disconnect box, then used the cording that came with the compressor from the box to the compressor. The compressor cord is a very flexible stranded copper and the conductor is about twice the size of the 10-2 conductors. Its on its own 20amp breaker and hasn't tripped it yet.

 

[Norcal]

I just did a similar compressor - 3.8hp motor on it, on a pretty long run of about 80 feet from the panel.

I used 10/2 AC90 to a disconnect box, then used the cording that came with the compressor from the box to the compressor. The compressor cord is a very flexible stranded copper and the conductor is about twice the size of the 10-2 conductors. Its on its own 20amp breaker and hasn't tripped it yet.

Using flexible cord without a plug does not comply with the NEC, can't comment about the CEC.