Can I run a 5HP machine on this circuit?

[Brian W Evans]

When I bought my current house, the garage had been used as a woodshop at some point in the past. It has a separate electrical subpanel with a couple of 220V circuits, which are, according to the breaker switches, 40 amp circuits. Is there any way of knowing, based on this information, whether I can run a 5HP machine on these circuits? I believe I need 10ga wire, correct?

Thanks for any guidance you could offer. I am, as you can tell, electrically challenged.

[Brad Sperr]

I know there are some calculations you can do, but I've heard 5 amps current draw per horsepower at 240v is a good rule of thumb. I think a 40amp breaker should be more than enough to power your table saw, assuming that you don't have any other big loads on the circuit.

[Howard Norman]

Yes, I believe that you will be OK running a 5HP machine on a 40amp 220 volt circuit. I have always used #8 wire for 40 amps myself and #10 for 30 amp circuits.

[Kendall Landry]

The owners manual will tell you what size circuit to use. If it were me, I'd put at most a 30amp breaker and at least 10ga wire and 30amp recepticle/plug for a 5hp motor unless the manufacturer says otherwise.

[Sam Layton]

Hi Brian,

You need a 30 amp circuit with a 10 ga wire, for a 5 hp machine. You say you have a 40 amp circuit. That will run your 5 hp machine just fine. However, that 40 amp circuit will require an 8 ga (I think 8 ga) wire. If your 40 amp circuit does not have an 8 ga wire you will need to change out the circuit breaker. 30 amp is 10 ga, 20 amp is 12 ga, and 15 amp is 14 ga.

I use 30 amp 10 ga for my 5 hp machines, and 20 amp 12 ga for 3 hp machines.

Sam

[Rod Sheridan]

Brian, the circuit size will depend upon the motor full load current, not the motor horsepower.

Check your motor nameplate for more information.

A 40 ampere circuit is larger than you need, you might consider using it to supply a small distribution panel to power a couple of circuits.

Regards, Rod.

[Brian W Evans]

Thanks for all the help. It seems like I've got what I need to run the 5HP motor, and then some.

[Chris Padilla]

For the future, you can do a simple calculation based on Ohm's Law:

Power (watts) = Current (amps) * Voltage (volts)

There are 745.7 watts per horsepower. 5 hp = 3728.5 W

Current = 3728.5 W / 240 V = 15.5 A

This will get you started but as Rod stated, you need to look at the motor's faceplate for more definitive information.

As Sam stated, for most cases, 5 hp motors on 240 V/30 A circuits work just fine and in a fair number of cases, it'll work just fine on 240 V/20 A circuits, too. It all depends on the motor.

[Chris Friesen]

For the future, you can do a simple calculation based on Ohm's Law:

Power (watts) = Current (amps) * Voltage (volts)
There are 745.7 watts per horsepower. 5 hp = 3728.5 W
Current = 3728.5 W / 240 V = 15.5 A

You forgot to include efficiency and power factor in your formula. In real life, a good rule of thumb is 5A per HP at 240V. More efficient motors will draw less than this, and some will draw more, but this will get you into the ballpark. Then round up to the nearest standard circuit current rating.

Generally speaking, a 15A circuit will do 2HP, a 20A circuit will do 3HP, and for 5HP you need a 30A circuit. (All at 240V of course.)

[Gary Radice]

Your question has been answered but I'm curious: what machine do you have that runs a 5 hp motor?