Wiring 220V Compressor

[adam1961]

Jeff,
I misspoke, I am renovating and was sitting here looking at the 40A line stubbed out for a cook top. Yes, a dryer is typically 30A
My smaller 5hp compressor draws 21.8A running, and does fine on a 30A line.

Do they enforce the line of sight disconnects in a residential application in AZ? Here, it is only enforced in commercial / industrial applications. It is common sense though and a good safety factor.
We also only have to size a circuit based on 125% of the load if the load is continuous. I forget what the definition of continuous is with respect to the code. Is is 4 hrs? Again, this is what is enforced. I always set up my circuits to never be loaded at more than 80%. Any time I have doubts, I am on good terms with the electrical contractor that we use at work and often get a lot of advice and they make sure I am safe.

Adam

[jeff-register]

Adam,
I go by the national electric code. If an inspector disagrees he or she MUST prove you wrong in the NEC book. Your 5hp compressor you forgot to tell me what voltage you are running at so no calcs can be made. Let’s assume 120vac. At 120 volts your compressor draws 27.25 amperes@125% Now you have a 30 ampere service & by code should use no more than 80% which is 24 amperes. You are overloaded by 3.25 amperes. Do you have a clip on ampmeter to check actual current draw? I have two to check one against the other. A guy can never tell when a tool goes south so a second meter is good to have away from the shop. Now if you are running 240 volts calculate it again please. Have you ever worked with a delta wye config? It has a delta config but two wires are 120 to ground, The third wire is 240 to ground. That form of three phase was used here in Arizona to get hermetic type compressors started easier. I have repaired air conditioning by using a bag of ice. The compressors have a thermo switch on the tops of the compressors. I cooled off the compressor with a bag of ice till the thermo switch closed again & we had air conditioning again. It was a very hot 118 degree day that summer. A few summers back the airport stopped flights. THe density of the air went off the charts & the controllers could not calculate the lift of the wings to get them to fly out & drop like a rock coming in. WE pay very close to the temps here in Phoenix.
I have gone too far not talking about marine stuff so lets go to e mail.
Jeff

[Doug Wilson]

Have to agree with what Jeff, said not an electrician but an engineer. Think if it was me would
run a dedicated circuit for the compressor and put a disconnect on the wall beside it better safe than
sorry. Besides will not stop your wife from doing laundry.
Doug

Doug

how is it motors multiply when the garage lights get
turned off?

[jeff-register]

Be sure to put the guard over the pullys to keep little fingers from getting inside. At TRW we had machines built by us with all the protection required.
Next thing we knew someone was pushing buttons & hurting others. We were all adults too.

[slim60]

I agree with Jeff and ddwilson. Be safe. Run conduit from service panel to compressor. You can mount a disconnect there close by. That’s the way it would be done to code in a commercial building. Again, be safe. This is your home. And family. A compressor is a valuable piece of equipment in any shop. Have fun with it.

[Mumbles]

The 220 compressor I have in the garage isn’t hard wired in but has a cable rolled up on it which plugs into the 50 amp welder outlet at the opposite end of the garage. Inside the switch box on the compressor are two 35 amp fuses which do blow occasionally on start up if it’s really cold.

---

Attachments:

[jeff-register]

Mumbles,
I’ll look in my pile of fuses. I have many left overs from my business. I will send you some that will work. SEE everyone why we rate the compressor at 125%. Jim needs dual element slow blow fuses maybe or the cap start may be failing. The cap injects voltage at start up at 45 degrees electrical degrees to get it spinning. If the cap is weak it will blow fuses. Remember I called for a 50 amp service fused down in my post guys? A three phase system is light years better as it has 120 degrees & power at every phase to get it started. Send me an E Mail @ jeff.50@cox.net..
Jeff

[Mumbles]

Thanks, but that’s OK Jeff. I can get the fuses at Home Depot around the corner.

[vintin]

Is the service entrance in the basement? If so, could the compressor be placed near it? Putting in a separate receptacle and breaker for it wouldn’t take much drywall work. You could then run air lines where you wanted.

Plugging and unplugging 240v is a pain plus can be a bit of a hazard. You know you will forget sometime and leave the wife having to do it. Leaning over a metal dryer tugging on a 240v plug can be a hard pull. One touch of the hot is all it takes.

[jeff-register]

No need for a plug & recept. Using the fusable disconnect is your means of disconnect. Just get a one armed disconnect to pull down to disconnect power with the cover closed, Very safe. The circuit breaker is the disconnect for the wire run. Keep it simple & cheap too. A 50 amp 250 volt recept will cost around $50.00 & the cord cap is the same. Save the $100 & use a 60 amp nema 1 disconnect fusable box & run S.O. cord to the compressor motor. Much less money too!

[Author]

Posts