Cord connected motor tripping breaker

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Eddie J.

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Elkins, NH USA
Baffled on what to do, Cord connected portable metal chop saw tripping breaker as customer bares down it. Did some field readings on this circuit located in a knife makers shop and everything is fine until he gets into cutting the steal. He needs to cut the steel at 1500 degrees quickly and can only use the abrasive style wheel. Placing the chop saw under a heavy load for a short time maybe 1 to 2 minutes. The saw starts to reach locked rotor 35amps measure before the breaker trips. Pretty obvious so far. The existing circuit is a 20 amp 120v, saw has a rating of 15 amps. This making it a cord plug situation. Hmmm, "other craftsmen aren't having the problem in there shops". Any suggestion? I can't fix this issue under our guide lines. Our articles all refer to starting, is there an exception I'm missing someplace in the code. I don't think so. I left it with him to try an industrial/commercial saw. Just trying to exhaust all angles.
 
If the motor is protected internally with overloads then you use an overcurrent protective device (breaker) rated 250% of the full load amps. Look at Table 430.52
 
Welcome EddieJ to the forum.
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Eddie J. said:
Baffled on what to do, Cord connected portable metal chop saw tripping breaker as customer bares down it. Did some field readings on this circuit located in a knife makers shop and everything is fine until he gets into cutting the steal. He needs to cut the steel at 1500 degrees quickly and can only use the abrasive style wheel. Placing the chop saw under a heavy load for a short time maybe 1 to 2 minutes. The saw starts to reach locked rotor 35amps measure before the breaker trips. Pretty obvious so far. The existing circuit is a 20 amp 120v, saw has a rating of 15 amps. This making it a cord plug situation. Hmmm, "other craftsmen aren't having the problem in there shops". Any suggestion? I can't fix this issue under our guide lines. Our articles all refer to starting, is there an exception I'm missing someplace in the code. I don't think so. I left it with him to try an industrial/commercial saw. Just trying to exhaust all angles.
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They may be. I recall burning up 3 bench grinders in 5 months b/c I was using a polishing wheel on extruded aluminum to make it shine like a mirror; motorcycle swingarm.

Even if the breaker doesnt trip, running any kind of regular chop saw under full load for two minutes will kill the saw in short order. Imo, in this case, the customer does indeed need a larger/different/industrial type saw that wont be run at maximum/near-LRA for such a long time. Rewiring using #10 on an individual branch circuit to minimize voltage drop and/or switching to a 240V tool would help. It sounds like your customer is using a saw that, no pun intended, isnt cut out for the job.

eta: any way to use a grinding wheel with a thinner kerf to reduce the motor load while still cutting the steel in an acceptable timeframe?
 
He needs a different saw or a different technique.

I disagree that this can be put on a larger breaker.

If you were to increase the breaker size soon enough the motor will smoke.
 
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