20amp machine on 30 amp circut?

[Mark Bolton]

I couldn't use my machine on a 30 ampere circuit.

Regards, Rod

Well you could, and it would likely run forever but you would void the warranty right? The manufacturer is trying to add another level of protection to cover their behind.

Mark

[Dave MacArthur]

Rod, that's interesting--I'll have to look through my manuals for that, haven't noticed it in the past.

Stephen, I'd guess that anyone willing to put in extra safeties to a system like sub-breakers or thermal fuses wouldn't be wrong, and it's one more layer of protection. I'd feel totally comfortable in this case just following the conservative NEC calculations, and using 10AWG wire, since I know that no matter what the motor does, it can't pull enough current to heat the wire up to dangerous levels and the circuit is well protected at both ends by the motor's thermal overcurrent as well as a CB sized for the wiring. While it may seem odd to have a disparity between branch circuit wire size and the extension for the actual load, when looking at a large wire, just a few seconds thought will remind you that this is in fact the norm, as Will Overton says.
- 1A clock on 15A circuit
- 2A kitchen appliances on your 20A kitchen circuits
- 10A hair dryer on 15 or 20A bathroom circuits.
- 0.2A transformers for your cell charger etc. plugged in all over the house with 18ga wire
There is no safety impairment or negative correlation between a circuit sized to allow a MAXIMUM FLOW of 20 or 30A without heating up, and using less than maximum loads on that circuit... that's how the whole thing is engineered to work.

[Chip Lindley]

...3HP motor on 690 must use 17A from NEC tables for FLC...

??? WhaTheHay is 690? Is that a high voltage indiginous to Arizona to deter illegal aliens??

[Greg Portland]

The circuit breaker protects the wiring to the outlet; NOT the machine.

OK, what protects the wire from the outlet to the fuse / protection in the tool?

[Dave MacArthur]

Greg, if any switch or overload protection device in a circuit opens... no current flows and it's all protected. The thermal overload protection on a motor actually, according to the NEC, is allowed and is planned to protect the motor, cord, and circuit wiring all the way back to the panel circuit breaker. The CB on a motor circuit (planned motor circuit IAW the NEC parts referenced in my post above, not just a circuit you've got a motor plugged into) protects for short circuit and ground fault. Of course, either will trip if their ampacity is exceeded, so they're both really protecting.

[Justin Jones RDH]

??? WhaTheHay is 690? Is that a high voltage indiginous to Arizona to deter illegal aliens??

It is a table saw i have- Grizzly G0690
I want to thank everyone so far for sharing your knowledge.
Best Regards,
Justin

[Rick Fisher]

Wow..

Up in Canada.. If the motor draws 20 amps.. it must be on a 30 amp circuit.. Code is that the breaker be 1.25 x the rated FLA of the motor. The magnetic starter has the job of protecting the motor, not the breaker box.

I have a 5hp table saw which has a FLA of 25 amps. My electrician insisted on putting in a 40 amp breaker because a 30 amp would not pass code. I believe code calls for no more than 2.5 x the FLA from the breaker, which would mean it was totally legal to run a 25 amp saw on a 50 amp or even a 60 amp breaker..

The motor draws the power, if the motor draws too much, relying on a circuit breaker to stop the over current is crazy..

I have a buddy with a Delta 15" Planer which they actually shipped with no mag starter.. He fried the motor on a 20 amp circuit.. Had he been running it with a Magnetic starter, it would have been no big deal..

[Rod Sheridan]

Well you could, and it would likely run forever but you would void the warranty right? The manufacturer is trying to add another level of protection to cover their behind.

Mark

Mark, it's actually the certification agency that requires the overcurrent rating restriction, not the manufacturer in this case.

It's actually very common to see such restrictions on many types of equipment due to withstand ratings of internal components.

Regards, Rod.