Electrical Circuit Breaker Question

[John Pahl]

Switches intended for motor control are rated for a maximum HP (inductive load) as well as maximum amperage. The HP rating is usually the more restrictive of the two values due to the tendency to arc across the contacts when breaking an inductive load. Note the HP ratings in the description of this switch.

Tom,
Thanks for the link. All My wire nuts are tight and all the connections to the outlets and plugs are tight so I've decided to replace the switch and breakers. Now I'm going to hijack my own thread....(kind of like steeling your own car). Do I buy a switch that is rated for the advertised HP of the motor or do I use ohm's law and covert to HP to get a real reading?

[Mike SoRelle]

Tom,
Thanks for the link. All My wire nuts are tight and all the connections to the outlets and plugs are tight so I've decided to replace the switch and breakers. Now I'm going to hijack my own thread....(kind of like steeling your own car). Do I buy a switch that is rated for the advertised HP of the motor or do I use ohm's law and covert to HP to get a real reading?

I tend to err on the side of caution and base switch selection on the motor nameplate, even if I know the thing will never perform at that rating. The obvious exception to that is the truly inflated specifications (think 12 'hp' shop vacs). Also make sure you take into account any other parts of the equipment (besides the motor) that will be operating at the same time.

Mike


Mike

[Rod Sheridan]

Greg and Sam sounds right the rating on the tools are RUN Amps that is approx 80% of the startup requirements (if it s a 10amp motor you will need a 12 amps (15 amp breaker) and FYI breakers will get weak with time or use so i would test them (fire + woodworking shop = one lost mind)

Actually, startup current on a motor will be in the 5 to 10 times full load current range, (or higher) depending upon supply impedance and the motor locked rotor current rating..........Regards, Rod.

[Travis Lavallee]

I would size the switch to be protected by the breaker on the circuit.

[Chris Padilla]

Regarding start-up current, try this:

My remote for turning my DC off and on decided to stop working on me and is stuck permanently in the ON position. This means the breaker becomes my switch. Well, the DC breaker is at the main panel of my house and the meter is right there. You should see how FAST that meter wheel spins when I fire up the DC! It perhaps jumps 1/2-3/4 revolution like a bat outa heck before slowing down to regular draw! LOL!

I agree with Travis on the size of the switch...just match it to the breaker protection rating.