wiring air compressor

[bobj49f2]

I have an air compressor with a 7 hp motor, the info tag says it draws 16.3 amps. I've been running it on an outlet that is about a foot away from the breaker box. The outlet was in the pole building when I bought it. I moved the compressor to a mezzanine in the back of the shop, about 40 feet away from the breaker box. The original outlet was wired to a 20 amp breaker using 10 ga wire. I didn't look in the box before running 12 ga. armored cable (BX) to the new location. I am using the original circuit breaker in the box. The amp charts I looked at said 12 ga. is good for 20 amps. I ran the compressor on the 12 ga. today and monitored if the wire got warm and I couldn't feel anything. Am I good with the 12 ga.? The compressor will be the only device run on this circuit.

 

[bobj49f2]

OK, I've been surfing the web for information on the motor on this compressor. I couldn't find the HP rating on the info tag, just the amperage. The tank under the compressor states 7hp. but this doesn't seem right. If it was it should be popping the breaker every time it starts up. Again, the breaker is 20 amps, from what I've been reading a 7 hp draws something like 30 amps. I'll look at it again tomorrow.

 

[OccupantRJ]

Around 746 Watts per hp. Amps x volts = Watts, so 16.3x220=3,586 watts. 3,586 watts/746= 4.80, so about 5 hp, by that calculation. Some manufacturers love to inflate hp figures. I would have used #10 wire to offset voltage drop, but you may be ok with the 12 as long as it fires right up. A motor 3 hp or larger should be hard wired with no plug, from my understanding. If out of sight of the panel, a disconnect should be used for servicing the unit. An AC disconnect will work.

 

[exranger06]

Do you have a brand and model # for the compressor?

 

[wyliesdiesels]

Around 746 Watts per hp. Amps x volts = Watts, so 16.3x220=3,586 watts. 3,586 watts/746= 4.80, so about 5 hp, by that calculation. Some manufacturers love to inflate hp figures. I would have used #10 wire to offset voltage drop, but you may be ok with the 12 as long as it fires right up. A motor 3 hp or larger should be hard wired with no plug, from my understanding. If out of sight of the panel, a disconnect should be used for servicing the unit. An AC disconnect will work.

Nominal voltage is 240 not 220

 

[bobj49f2]

I must have been half asleep last night when I posted. We were working out in cold all day insulating the pole building.

Anyways, the motor hp rating is listed as "SPL". I did a little searching and I think this might indicate the motor is 3-31/2 hp? We put it up in the mezzanine yesterday and I don't have good lighting up there yet. I replaced this more some years back and didn't remember what size it was. It's running a Campbell Hausfeld tri head compressor on a 60 gallon tank.

I drained the tank completely empty before moving it to the mezzanine. Once I had it up on the mezzanine I ran it full cycle to fill it and it seemed to work fine. Filled up at the normal rate. And and again, the 12 wire at the circuit breaker didn't show any sign of warmth.

BTW, the compressor came from the factory with a 220V plug, I've never had it hard wired into a disconnect.


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[alfredeneuman]

Around 746 Watts per hp.

That assumes 100% efficiency, and no motors on Earth are 100% efficient.

 

[Bert_]

Around 746 Watts per hp. Amps x volts = Watts, so 16.3x220=3,586 watts. 3,586 watts/746= 4.80, so about 5 hp, by that calculation. Some manufacturers love to inflate hp figures. I would have used #10 wire to offset voltage drop, but you may be ok with the 12 as long as it fires right up. A motor 3 hp or larger should be hard wired with no plug, from my understanding. If out of sight of the panel, a disconnect should be used for servicing the unit. An AC disconnect will work.

Also need to factor that a motor this size is probably 80% efficient. That makes it about 3-4 hp

Nominal voltage is 240 not 220

I think we need to use 230V since that is the rating on the nameplate.

 

[bobj49f2]

What does SPL, I think I read it means "split power load", mean? It seems it's a term used mainly for compressor motors. What do they rate them this way?

 

[alfredeneuman]

What does SPL, I think I read it means "split power load", mean?

It means "special", and it's a way of grossly inflating horsepower claims.

 

[Bert_]

I'm pretty sure it just means "Special"

The motor is not really 7hp so the manufacturer leaves it blank or SPL, then the compressor company can market it how they want.

 

[bobj49f2]

I can guess why they do it, to make their product look stronger, but is this a compressor manufacturer thing? I've never seen this on other motors. I have wired up a lot of pump and conveyor motors and never seen this.

 

[Bert_]

It is common on low - mid grade consumer items.

Stuff made for industry doesn't lie because they have a name to uphold and cheaply built / undersized equipment will cause problems when it get's used heavily.

 

[bobj49f2]

Yeah, I understand that. The original motor burned out about four years ago. A good replacement cost as much as a new compressor. I called the manufacturer and they gave me a name of a local parts distributor and got a replacement motor for $150~. It's been working OK so far.

My main concern was the wire from the box to the outlet.

 

[TRWham]

I can guess why they do it, to make their product look stronger, but is this a compressor manufacturer thing? I've never seen this on other motors. I have wired up a lot of pump and conveyor motors and never seen this.

Apparently you have never seen a vacuum cleaner. I have a 6 hp Ridgid with a NEMA 5-15 plug.

 

[bobj49f2]

Never dug into too alliances, I know they're usually cheaply built.