How many Amps does a 5 HP motor need?

[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.