Yet another compressor wiring question

[gatorgrabber]

I've been reading over the other threads but still have a question. I have a 5-hp Leeson 120554 that I just installed on an 80 gallon CH compressor. I'm running a dedicated circuit from my sub-panel that's about 8' away. My plan was to run a 30A breaker and 10AWG wire (in conduit) to a box next to the compressor. From there, perhaps a switch (still weighing a magnetic switch) and some armored cable to the compressor. I was thinking 10AWG (which I have on-hand) was fine but now have second thoughts.

Any advice?

 

[warren57]

I've been reading over the other threads but still have a question. I have a 5-hp Leeson 120554 that I just installed on an 80 gallon CH compressor. I'm running a dedicated circuit from my sub-panel that's about 8' away. My plan was to run a 30A breaker and 10AWG wire (in conduit) to a box next to the compressor. From there, perhaps a switch (still weighing a magnetic switch) and some armored cable to the compressor. I was thinking 10AWG (which I have on-hand) was fine but now have second thoughts.

Any advice?

What is the motor nameplate amps? I have a 5 hp 220 v motor on mine and I am about 10' from the panel. Piped in 3/4 conduit to the starter, then water tight flex from the starter to the motor. I used a 30 amp breaker and 10 ga. Copper wire. As I recall, my motor pulled around 22 amps. Should be about the same for any 5 hp motor (but you should verify yours). So a 30 amp circuit is more than enough. Mine has been running fine for several years.

 

[gatorgrabber]

It shows 20.8 FL Amps on the plate. Is what you're calling the starter actually the relay, or do you have a magnetic starter? Thanks!

FWIW, here's the motor info.

 

[pattenp]

If the HP on the motor data label is 5, to be wired to comply with NEC the circuit conductors need to be #8. NEC says 5HP FLA is 28A, so 28A x 1.25 = 35A. This is to comply with electrical code, I'm sure it will work fine on #10 with a 30A breaker if you don't care about wiring to code.

 

[gatorgrabber]

That's just it, I'm not one to cut corners. My motor plate states FLA is 20.8. So that times 1.25 equals 26A. I'm guessing this is one of the "5HP in name only" motors. So where does this leave me?

 

[pattenp]

What is listed in the HP space on the motor label? The FLA of 20.8 amps calculates to be a 5HP motor. But, the NEC table says to use 28A for 5HP when sizing conductors.

 

[gatorgrabber]

5 HP. Here's a link to the photo: https://www.dropbox.com/s/72tgbrclhajk0ho/2014-11-14 23.12.50.jpg?dl=0

 

[pattenp]

Technically by code because the HP is listed on the label, you need to calculate the conductor size using 5HP as 28 amps from table 430.248 even thought the data label on the motor says 20.8 amps. The thing is the motor would do fine with #10 on a 30A breaker, but I will only advise to wire it per NEC.

 

[gatorgrabber]

Understood, thanks for the clarification!

 

[Aceman]

If the HP on the motor data label is 5, to be wired to comply with NEC the circuit conductors need to be #8. NEC says 5HP FLA is 28A, so 28A x 1.25 = 35A. This is to comply with electrical code, I'm sure it will work fine on #10 with a 30A breaker if you don't care about wiring to code.

You're on the right track, but you have to remember that a 75 degree #10 wire is good for 35 amps in a motor application. So THHN or MC cable rated at 75 degrees would be just fine. Romex would still require #8 being it's a 60 degree cable.

For breaker sizing, the NEC would allow anything from a 35-70 amp breaker.

 

[gatorgrabber]

Are those degrees F or C?

 

[Aceman]

Celcius

 

[gatorgrabber]

Thanks

 

[pattenp]

You're on the right track, but you have to remember that a 75 degree #10 wire is good for 35 amps in a motor application. So THHN or MC cable rated at 75 degrees would be just fine. Romex would still require #8 being it's a 60 degree cable.

For breaker sizing, the NEC would allow anything from a 35-70 amp breaker.

Correct. I had tunnel vision and thinking of #10 NM being used and limited to 30A. Didn't come to mind that THHN @ 75C is good to 35A and the OP did say he was running conduit.

 

[gatorgrabber]

What I have on hand is 10/2 Romex and 3/4" conduit; so where does this leave me?

 

[pattenp]

What I have on hand is 10/2 Romex and 3/4" conduit; so where does this leave me?

First off, you can put romex in conduit, but it's a pain in the *** to pull. You really shouldn't put romex in conduit as a normal practice. You should use individual THHN wire. The other issue is the romex needs to be #8 to meet code. Don't you just love this!

Edit: Seeing that it's a short run just go buy some #10 THHN. Get Black for the hots and a green for your ground. If you want to be fancy get red for one of the hots and black for the other hot.

 

[gatorgrabber]

Lots of fun! It's only an 8' run with one 90° sweep, so that's not too bad. Let me dig and see if I have any #8 wire hiding somewhere...

 

[pattenp]

If you do use romex remember to re-identify the white as red or black by marking or taping the ends at the termination points.

 

[gatorgrabber]

Got my colored tape standing by. Still digging in the 'misc dept' for #8. Just to be clear, still use a 30A breaker??

 

[pattenp]

Got my colored tape standing by. Still digging in the 'misc dept' for #8. Just to be clear, still use a 30A breaker??

You can if you have a 30A on hand. If the compressor happens to trip it, which I don't think will happen, you can step it up to a 40A breaker. If you have to buy a breaker just get a 40A.

 

[gatorgrabber]

What do you know...I found three pieces of #8 THHN (green, black and red) that are 12' long! That doesn't happen very often. This will get me from the panel to the junction box next to the compressor. I still will need to buy wire from the box to the pressure switch, but that's only 3' and I'd like to have that armored. I'll assume, also #8? What about the wire from the pressure switch to the motor itself? #8 seems like overkill.

 

[600SL]

If you need to go out and purchase new wire I would keep it at 2 #8 and 1 #10 ground otherwise #10 should be fine. Any of these combinations should thread into 1/2" flex conduit. If you look inside the motor box you will find that you are probably connecting to #14's or #12's.