What size circuit for a 5 HP air compressor?

[Van Huskey]

Good point but I've never seen an IR compressor w/o overload protection on the motor. I'm sure that they exist though.

I would actually be surprised if any IR compressors lack overload protection, however I said it mainly since someone may read the thread with a low end cheapo compressor and might make a poor decision.

[Kevin W Johnson]

I guess I'll have to spend the $30 for a 20 amp locking plug and receptacle then. I was really hoping to avoid that expense. I have no idea why they would have put a 15 amp plug on something that draws a full 15 amp. It is a molded cordset so nobody replaced the plug. The darn thing is I think I have 20 amp locking receptacle somewhere, but it isn't in my box of electrical stuff.

I was looking at some Leeson motors and most of their 3 HP motors show 13 amps full load. It is really hard to know how many amps a "real" 5 HP motor should draw. All I know is this motor is not a full 5 HP if it draws only 15 amps.

Do you have a clamp meter? Or access to one? I'd be curious what the actual amp draw is.

[Rick Fisher]

Compressor manufacturers do that all the time.. its a price point thing .. As someone said, a typical 3hp motor will draw 13-18 amps.. Its a 3hp motor. Typically the motor will run 65% of FLA .. maybe a bit more ..

If the stock cord is a factory cord, just use it .. Its fine..

We see lots of woodworking machinery with actual 5hp motors and spindly little cords because the actual cord is very short..

The other thing compressor manufacturers lie about is CFM .. developed or delivered.. Generally an advertised 12 cfm compressor will actually only deliver 9 cfm .. Its a sleazy business..

[Rod Sheridan]

I guess I'll have to spend the $30 for a 20 amp locking plug and receptacle then. I was really hoping to avoid that expense. I have no idea why they would have put a 15 amp plug on something that draws a full 15 amp. It is a molded cordset so nobody replaced the plug. The darn thing is I think I have 20 amp locking receptacle somewhere, but it isn't in my box of electrical stuff.

I was looking at some Leeson motors and most of their 3 HP motors show 13 amps full load. It is really hard to know how many amps a "real" 5 HP motor should draw. All I know is this motor is not a full 5 HP if it draws only 15 amps.

Brian, just buy a straight blade receptacle and cap unless you have a need for a locking receptacle such as a cord hanging from a ceiling..........Rod.

[Van Huskey]

If the stock cord is a factory cord, just use it .. Its fine..



..

That was/is my opinion.

[Bob Coleman]

You can put a 15A receptacle on a 20A circuit as long as its not the only receptacle, and a duplex receptacle counts as two (this is not true for circuits higher than 20A). 15A receptacles are rated for 20A pass-through. Like Van said, as long as the plug will fit in the receptacle you are fine (and someone like my house's previous owner didn't do a hatchet job on it)

I almost certain there's no distinction here for 120V vs 240V, but if there is someone please correct me.

[Brian Elfert]

You can put a 15A receptacle on a 20A circuit as long as its not the only receptacle, and a duplex receptacle counts as two (this is not true for circuits higher than 20A). 15A receptacles are rated for 20A pass-through. Like Van said, as long as the plug will fit in the receptacle you are fine (and someone like my house's previous owner didn't do a hatchet job on it)

The thing is, this will be the only receptacle on this circuit.

I think I am probably going to spend the extra money on the locking plug and receptacle. The locking stuff is so much more substantial. A regular 20A 250V plug isn't much more than a regular 115 volt plug with a prong turned 90 degrees.

[Kevin W Johnson]

You can put a 15A receptacle on a 20A circuit as long as its not the only receptacle,

Something about that seems wrong to me. That would allow someone to pull 20A thru a single 15A receptacle.

[Matt Marsh]

Something about that seems wrong to me. That would allow someone to pull 20A thru a single 15A receptacle.

If everything is sized correctly, any tool or appliance with a 15 amp cord and plug installed is limited to 12 amps max, as per table 210.21(B)(2) of the 2011 NEC. Tools or appliances with 20 amp cord and plugs are limited to 16 amps. Again if everything is sized according to NEC requirements, any appliance or tool with a 15 amp cord and plug installed should never draw more than 12 amps maximum. If a particular appliance or tool draws greater than 12 amps, but no more than 16 amps, this code section requires that it have a 20 amp plug configuration installed. Inversely, the only times that you need a 20 amp receptacle installed on a 20 amp circuit is when your appliance or tool has a 20 amp cord and plug installed, or if as stated earlier, the 20 amp circuit circuit only supplies one single receptacle.

Article 210.21(B)(3) of the 2011 NEC allows installation of 15 or 20 amp receptacles on a 20 amp circuit, as long as the circuit supplies two or more receptacles. As someone stated earlier, a duplex receptacle counts as two receptacles.

[Mark Norman]

Do the math.

1 HP = 746 watts.

5 HP X 746 watts = 3730watts /220v = 16.95 amps. Twice that many on a 110 outlet, that would be 33.9 amps. It would pop a 20 amp breaker every time it was turned on.

Not just sometimes, but every time.

The difference is; a motor seldom produces more power than is needed at any given time. So an electric motor capable of 5 HP will almost never see a 5 HP load.

A motor with 5 HP on the nameplate will be happy as a clam producing 2 HP all day long and have no problem on a 110 volt 20 amp breaker.

For the record, a circuit breaker is NOT intended to protect the appliance. Its purpose is to protect the circuit up to and including the receptacle except in industrial applications where the appliance is hard wired. In that case, it must have its own service disconnect which may or may not be in the form of a breaker.

Just my 2 cents.

[Matt Marsh]

Do the math.

1 HP = 746 watts.

5 HP X 746 watts = 3730watts /220v = 16.95 amps. Twice that many on a 110 outlet, that would be 33.9 amps. It would pop a 20 amp breaker every time it was turned on.

Not just sometimes, but every time.

The difference is; a motor seldom produces more power than is needed at any given time. So an electric motor capable of 5 HP will almost never see a 5 HP load.

A motor with 5 HP on the nameplate will be happy as a clam producing 2 HP all day long and have no problem on a 110 volt 20 amp breaker.

For the record, a circuit breaker is NOT intended to protect the appliance. Its purpose is to protect the circuit up to and including the receptacle except in industrial applications where the appliance is hard wired. In that case, it must have its own service disconnect which may or may not be in the form of a breaker.

Just my 2 cents.

Mark,

If this were indeed a true 5HP motor, it would draw much more than 16.9 amps @240 volts. It could be as low as around 25 amps for a very expensive premium efficiency model, but more than likely 26-28 amps for something more standard like they would install on this air compressor. The 2011 NEC table 430.248 lists a 5HP single phase motor connected to 230 volts at 28 FLA. If it did not have internal overload protection, you would need to provide external overcurrent protection (heaters), and size the circuit conductors and the short circuit/ground fault protective device according to NEC requirements. This would require you to multiply the FLA value from table 430.248 times 125%, which would give you 35 amps. The 75 degree column of table 310.15(B)(16) list a #10 copper conductor at 35 amps, which would be the minimum size conductor you could use for a true 5HP motor (before any necessary derating is applied). If you were feeding the circuit with a standard inverse time circuit breaker, you could go as large as 250% of 28 FLA, which comes out to 70 amps.

But this motor is obviously not a true 5HP model, and it probably does have internal protection. With a lot of these types of tools, the nameplate data is pretty much useless, and you have to instead go by the manufacturer's recomended circuit size.

[Al Wigfall]

I have a used Ingersoll-Rand air compressor I need to supply power to. It has a true 5 HP motor that says it takes 15 amps 230 volts on the motor data plate. The compressor has a 14 gauge cord with a 15 amp 230 volt plug on the end. (I have no manual and not available online.)

It seems to me that something that takes 15 amps continuous would need a 20 amp circuit. Why the 14 gauge cord and 15 amp plug then? I assume it would be okay by electric code to put a 15 amp receptacle on a 20 amp circuit? I know that putting a larger plug on a smaller circuit would be a violation.

Hi Brian,

I work for Ingersoll Rand and reached out to one of our product support supervisors for his opinion on your question. Here is what he responded with, "Our 5 HP compressor should not be on a plug of any kind. Our manual specifically states, “The electrical installation and service must be performed by a qualified electrician who is familiar with all applicable electrical codes”. The NEC Code 430.52 is dedicated to compressors for proper installation. The running amps or FLA (full load amps) as stated are 22.5 but at start-up, it will spike to 2.5 times the full load amps. Ingersoll Rand strongly advises all customers to hire a licensed commercial electrician."


Hope that helps!

Al Wigfall
Social Media & Digital Leads, Ingersoll Rand

[Chris Friesen]

I work for Ingersoll Rand and reached out to one of our product support supervisors for his opinion on your question. Here is what he responded with, "Our 5 HP compressor should not be on a plug of any kind."

Interesting. I'm curious why he would say this in the context of a home shop. Technically section 430 is for circuits designed from the beginning to supply only motor loads, otherwise Article 210 applies. Also, 430.42 allows motors to be connected to general-purpose circuits via cord-and-plug as long as the device in question (ie the compressor) has built-in overload protection.

These two things taken together explains why most home woodworking equipment (which are arguably motor loads) are normally connected to "regular" branch circuits via cord-and-plug. If section 430 really did apply we could do things like massively oversize the breakers relative to the wiring--but most people don't do that because the next owner will not have any clue what's actually in the walls so it's safer to treat them as "regular" circuits.

[Michael W. Clark]

If this were indeed a true 5HP motor, it would draw much more than 16.9 amps @240 volts. It could be as low as around 25 amps for a very expensive premium efficiency model, but more than likely 26-28 amps for something more standard like they would install on this air compressor.

Matt, is it possible that the 26-28 amps you list already has the efficiency and 25% safety factor in it? A Grizzly 5HP TS recommends a 30A circuit single phase (220-240V).

Mike

[Kirk Poore]

First off, if that is a true 5 hp motor, you need a lot more than 15 amps at 230V to run it. Even a Baldor high efficiency 5 hp motor needs at least 23 amps at 230V.

CPeter

The Baldor 5 hp 1ph motor on my Oneida DC takes 19.5 amps @ 230V. I have it on a 30 amp circuit, and it runs fine. Most circuit breakers will allow a brief overcurrent (up to a certain amount) before they trip to allow for motor starting issues like this. That being said, a compressor may be a harder starting load than a dust collector.

Kirk