How many Amps does a 5 HP motor need?

[Bob Slater]

I will be Hooking my compressor up to my fuse panel and need to buy a circuit breaker. It is a 5.0 HP 230 Volt single phase motor. I phoned customer support from the mfg, but am not convinced I got the right answer. They said to use a 40 amp breaker. The motor draws 22 amps from what I can see on the website. Just a gut feeling a 30 amp circuit is the right one. Anyone know for sure?

[Dennis Ford]

Hi Bob
Use a 40 amp like they recommended if at all possible. The motor is probably rated for 22 amp continuous and will pull a lot more during starting. You might get by with a 30 amp breaker with only occasional trouble but why hassle with it?

[Mike Henderson]

Remember that the breaker is to protect the wiring so if you're going to use a 40 amp breaker, make sure your wire in the circuit will handle 40 amps.

Mike

[Doug Shepard]

40A and 8 ga wire was what the folks at the elec supply house said to use for the contactor switch & breaker when I wired up my 5HP ClearVue cyclone.

[Andrew Nemeth]

Doug, How long was your run? I know you have to upsize wire for longer runs.

[Jim O'Dell]

My 5hp Clear Vue is on 10 guage and 30 amp breaker. Never a problem. In fact, that was what Leeson recommended for the motor, IIRC. My run is only about 14' max from the breaker. Jim.

[Von Bickley]

My 5hp Clear Vue is on 10 guage and 30 amp breaker. Never a problem. In fact, that was what Leeson recommended for the motor, IIRC. My run is only about 14' max from the breaker. Jim.

I agree with Jim......
I would think #10 on double 30's would be fine.

[Bob Slater]

I am pretty sure I ran 30 Amp Wire under the drywall, so I guess I better not go bigger than a 30 amp breaker. Will double check the wire tomorrow. Thanks for the replies. My table saw is also a 5 HP General and it is running fine on twin 20 amps breakers.

[Doug Shepard]

Doug, How long was your run? I know you have to upsize wire for longer runs.

From the breaker box to the motor only about 20-22 ft. When the supply house consulted some tables and the info from the motor, they said I could go with 30A but said it was only about 2A from potentially popping the breaker. I'm no electrician and went with their recommendation. I think it was startup current draw they said might pop the breaker IIRC, not the normal operating current.

[Bruce Page]

I run my 5hp Woodmaster sander on 30amp/10ga without any problems but I would run a 5hp compressor on a 40amp/8ga due to the higher loads, particularly on startup.

[Tom Veatch]

...It is a 5.0 HP 230 Volt single phase motor. ...

A 30a circuit is fine for a 5HP motor. Unless you've got an extraordinarily long wire run 10ga wiring is also fine. The start surge on a 22 FLA motor won't trip a properly functioning 30a breaker unless the motor is locked up, otherwise defective, or is trying to start under a high static load. Modern compressors have unloader valves that reduce the startup loads so that it should be no harder starting than an equivalent motor spinning up a heavy blower wheel in a DC/cyclone.

[Rod Sheridan]

I will be Hooking my compressor up to my fuse panel and need to buy a circuit breaker. It is a 5.0 HP 230 Volt single phase motor. I phoned customer support from the mfg, but am not convinced I got the right answer. They said to use a 40 amp breaker. The motor draws 22 amps from what I can see on the website. Just a gut feeling a 30 amp circuit is the right one. Anyone know for sure?

Hi Bob, check the motor nameplate for full load current, don't rely on the web site. You never know if the motor is a different model/manufacturer from the "typical" information presented on the site.

Unless your motor is substantially different from what you said, a 30 Ampere breaker is the correct choice.

Regards, Rod.

P.S Asking how many amps a 5 HP motor needs isn't a question that can be answered. A high quality high power factor/high efficiency 5HP motor may be as low as 18 amperes, or as high as 28 if it's a low efficiency/low power factor motor. That's why you need to obtain the motor full load current from the motor nameplate....Regards, Rod.

[Chris Damm]

A compressor has a much higher starting load unless it is empty. If it restarts under partial pressure you will want a 40 amp breaker and 8ga. wire. Why would you doubt the manufacturers recommendation??????

[Chris Friesen]

I run my 5hp Woodmaster sander on 30amp/10ga without any problems but I would run a 5hp compressor on a 40amp/8ga due to the higher loads, particularly on startup.

Most big compressors have a bypass at startup, so they work the hardest when almost full.

[Chris Friesen]

The manufacturer may recommend an oversized breaker just to minimize any hassles--it's no skin off their back if you spend more money than necessary. Also, a larger breaker doesn't necessarily mean a larger conductor.

Note: the following is vastly simplified. Read the NEC for the fine print.

You have two choices. You can treat it as a standard plug-and-cord connected device, in which case you need a conductor of 125% the full-load rating on the nameplate, and a breaker to match. If your motor is rated at 24A or less you can use #10 and a 30A breaker.

Alternately, you can call it a dedicated motor circuit. The conductor ampacity requirement is the same as above. The advantage of calling it a motor circuit is that you're allowed to oversize the breaker to deal with startup surges. The normal limit for an inverse-time breaker is 2.5x the full-load rating, but if necessary this can be increased up to 4x the full-load rating.

Yes, this does mean that the breaker is rated for more current than the conductors, but this is explicitly allowed for motor circuits.

[Bob Slater]

A compressor has a much higher starting load unless it is empty. If it restarts under partial pressure you will want a 40 amp breaker and 8ga. wire. Why would you doubt the manufacturers recommendation??????

I doubted it, because I always double check info I get over the phone. When I was on the phone I went from the secretary to a guy who seemed completely vague about the needs of the compressor. You never know who exactly is answering the customers queries these days..

[Chip Lindley]

For all intents and purposes, your compressor will run fine on 30A/10ga. If your wiring is already buried in the wall, go with the breaker sized for that gauge wiring!! If you are installing NEW, then go 40A / 8ga. *just because*!!

[Derby Matthews]

Mine's also a 5hp 1ph motor rated at 24 amps. When I hook up my fluke inductive ammeter to one of the leads in the service panel the motor draws over 70 amps (inrush amps) at startup (tank nearly full). My run is about 30 ft. It is a dedicated circuit, while the 20 amp circuits in my one man shop are daisy chained for the sub 1 hp loads of most other machines (wired to 220 to run them cooler)

Long and short, I decided to use 10 gauge wire to handle the full load rating of 24 amps, and put in a 40 A breaker to avoid tripping, mentioned above as allowable on a dedicated motor circuit. BTW Every time a magnetic breaker overload trips it becomes fractionally less able to handle overloads without tripping again more and more often. There's no cost savings in frequently replacing a prematurely worn-out breaker - not to mention the potential fire safety issue.

[Eric Gustafson]

Yes, this does mean that the breaker is rated for more current than the conductors, but this is explicitly allowed for motor circuits.

Not challenging you Chris, since I am no where near educated about the subject, but can you give the NEC reference for the allowance?

I have a Clearvue on 10 gauge wire that sometimes trips the 30a breaker, but would want the code, chapter and verse before I go and change anything.

[Derby Matthews]

You can find a current copy of the NEC code book at most good-sized libraries across the US. In mine they wont let you borrow it but will allow photocopying of needed pages for your personal use. Also very helpful is Wiring Simplified" 41st edition (by Richter, Schwann, Hartwell), available at most Home Depot Stores in the Electrical Dept. W.S. will give you the Readers Digest information and refer you to the code in areas where more detail is required, such as the allowable number of wires in a raceway, rules for dedicated motor circuits, etc.
FYI the code is HUGE and in multiple lb. large bound book that can be lain flat for copying. I wouldn't recommend any layperson to attempt purchasing it. The library is your best option IMHO. There's an online version if you dont have library close by, but I find the printed version much easier to access and cross-reference.

[Tom Veatch]

... NEC reference for the allowance...

NEC Article 430 covers motor circuits, which, in my opinion, should never be mentioned in other than dedicated, hardwired, continuous use, industrial/commercial environments.

[Matt Armstrong]

For all intents and purposes, your compressor will run fine on 30A/10ga. If your wiring is already buried in the wall, go with the breaker sized for that gauge wiring!! If you are installing NEW, then go 40A / 8ga. *just because*!!
spoken like a man who hasn't run 8awg in a while, i can tell!

[Mike Hicks]

I would check the motor nameplate to see what it says rather than rely on what some guy in customer service says. It's not his shop that is going to burn down if the wiring overheats and catches fire. Wire the circuit with the gauge appropiate for the current draw of the motor. Wiring is not a place you want to take chances.