Why did my circuit breaker trip?

I bought a 12a band saw a few weeks ago and have put a lot of hours on it. It goes through 5" of oak pretty nicely.
Tonight I was cutting 3/4" luan, which is reasonably soft. The breaker tripped. It is a 20a breaker, #12 wire, and nothing else on the circuit. I reset it, and finished what I was doing.
I have used a heavily loaded 15 sander on the circuit, so I am a little perplexed as to why the breaker would have tripped. It is about 2 years old.
Any ideas, other than a defective breaker?
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Could there have been a sag or dip in the line voltage? Did you happen to notice the lights dim around this time?
If the saw is drawing close to the maximum capacity of the circuit, a drop in voltage could be enough to push it over the edge.
Cheers, Paul

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You would proly have to put an ampprobe or some kind of ammeter on the machine to see what the load really is. Soft material, depending on how fast you feed it, can generate more "chip load" than hard material, and actually load the motor more than hard material as it binds the blade more. In harder material, the chip load is less, as the blade "skates" more.
Also, sometimes breakers just trip! Sometimes vibration makes them trip. If you load a breaker just shy of the trip point, it could cock, like a mousetrap, and trip later on. The key is to determine a trend in events. -- Mr. P.V.'d formerly Droll Troll

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You may have a defect in the saw's motor, the cord, the plug. Test it.
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Other possibilities include that you twisted the workpiece, pinched the blade, and stalled the motor, that you stopped, and tried to re-start with the blade still engaged, or that you just kept the saw under continuous load for longer than you usually do when cutting oak. You imply that this is a dedicated circut, so I'd check for scorch-marks at both ends, but otherwise, forget about it unless it happens again.
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