Breaker capacity

[Wes Billups]

I just purchased a new 5 hp tablesaw and the motor is rated at 19.8 amps. The current wiring is 12 gauge on a 20 amp breaker. Will this be sufficient to start this tablesaw?

I wasn't sure if the in-rush of power needed to start the saw will trip the breaker. If I need to correct the wiring I'd rather do it now than down the line.

Thanks,
Wes

[Rod Sheridan]

Hi Wes, unless the line voltage drop is excessive, you should be OK.

If it starts, you're fine, and for home use I wouldn't bother going to a higher capacity circuit.

Regards, Rod.

[Prashun Patel]

Um, is that 19.8A at 220v? If yes, then you'll need to rewire yr feeder from the box. 5hps running 110v I think'd be a rare thing...

[Chris Padilla]

Breakers are designed to not trip with "start up" or "inrush" high current situations. The large current draw lasts for a very short period of time (less than a second, usually) and that isn't long enough to heat up the circuit breaker thus causing it to trip.

I'm with Rod, try it out first and see how it goes.

[Wes Billups]

I used 12/3 when I wired the shop. I'm only 8' from the subpanel so based on Rod's comments I think I'll go with what I've got.

Thanks,
Wes

[Chris Padilla]

Wes,

Shawn has a good point: is this 20 A circuit 240 V or 120 V? Still, give it the old college try and see how it goes.

[Jim O'Dell]

I've always heard that 5hp 220 motors need 10/2 wiring on a 30 amp (25 would work if it's available)breaker. Don't have a clue how the NEC reads for 5 hp motors. Jim.

[Von Bickley]

Wes,

For a 5 HP saw, you need to run #10 copper on 30 amp breakers... (Retired Electrician)

[Chris Damm]

"If it starts, you're fine, and for home use I wouldn't bother going to a higher capacity circuit."
Electricity is not something to play with. Switch to a 30 amp breaker and #10 copper wire!

[Tom Veatch]

...
I wasn't sure if the in-rush of power needed to start the saw will trip the breaker. If I need to correct the wiring I'd rather do it now than down the line...

As others have said, table saws are easy starting and the startup load is normally of such a short duration that you're not likely to have any problem with nuisance trips from that cause.

The FLA of the motor, 19.8 amps, is awfully close to the breaker rating, but you should be OK since you're not likely to be using the full 5HP for any extended period in a hobbiest application. If you do start making heavy cuts that use the saw's full power, then you might start seeing some nuisance tripping, but if you take it easy with the saw, you should be fine.

I'm assuming that you'll be plugging the saw into an existing branch circuit. If you're hardwiring the saw into a dedicated motor circuit, I'd expect the local jurisdiction and inspectors to insist on a 30 amp circuit based on the saw's maximum HP rating.

[Rod Sheridan]

"If it starts, you're fine, and for home use I wouldn't bother going to a higher capacity circuit."
Electricity is not something to play with. Switch to a 30 amp breaker and #10 copper wire!

That wasn't a sentence based upon no understanding of electricity. I'm an Electrical Technologist.

A 30 ampere circuit is not needed for a motor with a load profile like a home table saw.

If the 20 ampere circuit will start the motor reliably, the user is fine.

Regards, Rod.

[Bill Brady]

A 20 amp circuit is only to be loaded to 16 amps, this is to protect the wire from intermitent spokes in current such as the starting current of a motor. I would change to a 30 amp curcuit with #10 wire.

[Rick Christopherson]

A 20 amp circuit is only to be loaded to 16 amps, this is to protect the wire from intermitent spokes in current such as the starting current of a motor. I would change to a 30 amp curcuit with #10 wire.

No. That's not what code states, and the rationale you listed is also incorrect. A circuit can be loaded to 100% of its rating with non-continuous loads. This is a design issue behind the code so that you don't deliberately load a circuit breaker to 100% capacity continuously. However, if the circuit breaker is listed for 100% capacity, then you are permitted to load it to 100% for its entire life. The circuit breaker is there to protect the wire, and the thermal trip curves take into account the applicable heating aspects of the wire so that it will always trip before the wire exceeds its thermal rating.

Furthermore, a tablesaw is not considered continuous, and moreover, even when it is running, it rarely sees its full rated load.

[Bob Slater]

That wasn't a sentence based upon no understanding of electricity. I'm an Electrical Technologist.

A 30 ampere circuit is not needed for a motor with a load profile like a home table saw.

If the 20 ampere circuit will start the motor reliably, the user is fine.

Regards, Rod.

My 5HP General seems to run fine on it's 20 amp 220 circuit.

[David G Baker]

I agree with Von on the #10 wire and 30 Amp breaker. I try to add that little margin for protection against error. If the breaker is only 8 feet from the tool why not just change the wiring and breaker unless it is a major amount of work. I also have a tendency to agree with folks that have been in the trade (retired electrician) and have had the experience.