Reply by William Shelley

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William Shelley

595 posts in 1672 days

#1 posted 08-14-2017 05:57 PM

Need advice on power amperage. Planning on purchasing new Sawstop 3 hp rated at 220v 15 amps. My shop is primarily wired with 220v 50 amp outlets for welders. Can i run my 220v 15 amp equipment on a 220v 50 amp circuit without any problems? I have been running a 220v 15amp air compressor on the 50amp circuit without any apparent issues. Just want to make surethis wold not harm the electricmotors

- Rolle2259

It will certainly run it and no, it wont hurt the motors. The issue is having 50 amps of power available to a machine that is rated for 15. No, it wont hurt it in a sense of “overdoing it” as the amperage suggest, and yes you might have to change the plug to get the machine and the outlet compatible….but, there is a reason they rate electrical devices with an “operational” figure. If the saw is 15 amp rated you should not deliver more than required. It may be confusing because while the saw, when operating properly will only draw what it needs all is well and it wouldn t matter if you had it on a 200 amp circuit {in theory} it will still draw probably 9-10 on start up and 3-4 while running. Now, throw in a problem, like a short in the motor or switch and instead of tripping a breaker at 15 amps and stopping everything you still have 35 amps more before it trips…..what does all this mean? Well, you can start one heck of a fire and burn down the neighborhood with the extra amps now being delivered to the machine. You could also get shocked. You don t want to get hit with 220 anyway, but 15 amps or less is better than 50 for sure. It could also mean the difference between jamming the saw and tripping the proper breaker with no damage {15 amp breaker trips} or jamming the saw and blowing it up, getting you shocked and starting a fire {not tripping at 45 amps because you have a 50 amp breaker}.
For safety sake you really should run the proper rated circuits, you are not going to do that anyway, it cost money, I get it. I would suggest that you at least install the proper rated breakers.

- msinc

I m an electrical contractor and msinc summed it up perfectly! It s usually not that hard to do it the right way and you ll never have problems and have to worry about what could go wrong

- chrisirving

With all due respect, this is hogwash. I’ll explain:

The circuit breaker protects the wire.

The Motor must be protected by either a thermal breaker integral to the motor, or an external starting relay with an overload heater coil.

Even a 2HP motor on a 15A or 20A circuit is not “protected” by the circuit. It’s possible for an unprotected motor to be in a minor or moderate overload state for an extended period, without tripping the circuit breaker in the load center panel. This won’t make the motor catch fire right away, but it can rapidly degrade the winding insulation = dead motor.

-- Woodworking from an engineer's perspective

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