Motor Supply Cable Size

[Anthony Whitesell]

Per the motor plate, I have a Craftsman 1HP motor wired for 120V with a current rating (per the plate) of 12.2A. It is an older motor. I was making a lot of long rip cuts the other day and noticed the motor was very warm (not that I ever noticed before). I have wired the motor with 14ga 3cond SO cable. Should I move it up to 12ga? Or is the motor dying? (I have blown and cleaned it out already and the bearings in the saw and motor sound good)

Will the safety switch Rockler (http://www.rockler.com/product.cfm?page=17401) has on sale handle this motor?

[Sonny Edmonds]

... would be to look at the nameplate and connect it up for 240 volt operation.
Halves the amperage, and let's the circuit from the panel relax while your saw will run happier.
Anything I have that can be run on 240 does run on 240. I have myTS supply up front of the saw table so I can unplug it easily when changing blades. I plug my bandsaw or jointer in to the same plug when using one of them. ;)

[Dan Friedrichs]

Why would the supply cable size affect the heat output of the motor? (It doesn't).

The motor gets hot because the windings inside it have some small electrical resistance which converts some of your input power to heat. Electric motors like these are nearly entirely metal, and a little heat won't hurt them. You could have the biggest cable in the world connected to this motor, and it wouldn't change anything about how much heat it produces (**note to engineers: ignoring the slightly different voltage that might be applied to the motor with a cable with different Vdrop)

The switch you linked to will work (it's rated for 15A, your motor draws less than that).

[Anthony Whitesell]

Actually I know for a fact that if you under-voltage a motor it will get warmer. In my younger days, I tried to slow down 120VAC motors by reducing the voltage, the worked for a while until the magic smoke was let out. The utility company says the same thing when they drop a few volts during peak hours in the summer time to keep up with demand.

I know that when wiring a house with 14/3 NM-B cable the max breaker you can use is 15amp and 20 amp breaker for 12/3 NM-B. So my question really is at 12 amps (per the nameplate for what they're worth) over 12 feet of 14/3 SO cable is there enough voltage drop to cause the heat and how much of the problem could be resolved with 12/3 SO cable?

[James A. Wolfe]

The wire you have is rated to carry 15 Amps only due to an exception in the Code. The wire is physically capable of carrying more than that but has been derated for safety reasons. Voltage drop on such a short run will be negligible and well within accepted tolerances. The motor will heat as a normal byproduct of doing work. If you've never checked it before, odds are that it has always run this hot. If it is "dying", all the supply upgrades in the world won't stop the process.
Good luck,
Jim

[Chip Lindley]

All electric motors heat up when working to capacity. Only warm if running with no load. My planer motor is too hot to touch after a serious planing session, But it has not burned out or blown a breaker in 20 years! If your motor were actually dangerously overheating, you would smell *that motor smell* or see smoke before it toasted!

Your breaker would be tripping if the motor were drawing more amps than the circuit enjoyed. Your issue, so far, seems only to be a hot motor. My issue in the past, was a 14amp TS motor which repeatedly tripped my 15amp breaker during heavy cuts. Wire size had no bearing on this. Switching the motor to 230v solved the problem. The saw ran stronger with no more issues.

12-3 wire will certainly provide 100% of the voltage to the saw on this circuit. All the better if you can switch the motor to 240v. If the motor is 120v only, consider installing its own dedicated circuit from your panel. If you are using your saw on a circuit shared with lighting or appliances, the circuit will be overtaxed! Of course, check your motor for rough ball bearings or sleeve bearings which need oiling. Good Luck!

[Dan Friedrichs]

The voltage drop over 12' of 14ga supplying 12A is less than 1V. The line voltage can vary by 10V or more. So, no, this does not produce a serious voltage drop to your TS, and changing to 12ga will not produce any noticable effect.

[Roger Frazee]

Single phase motors 1 hp and less not automatically started are not required to have overload protection internal to the motor and depend on the circuit breaker to act in case of excessive current draw on overload. If the motor has a service factor of 1.15 or more it is designed to operate at about 25% overload for an extended period. This is very poor overload protection for motors. Interanl overload is much better.
If the motor is very hot to the touch you are very close to causing damage..warm is normal. Generally speaking on these small table saw motors ripping long lengths of thick stock like 2x4's is really pushing the motor specifications to maximum limits. You need to slow down your feed rate and keep the motor at correct rpm's. Approaching stall rates is damaging to the motor due to the excessive current draw and heat loss thru the motor windings. Try not to rip too much long stock at once. Let the motor cool if it gets warm. Then do a few more pieces.

[Anthony Whitesell]

I'll look for the service factor on the plate, but I didn't notice it. It does have internal overload protection built in (little red button on the motor). The next time it's a part I'll have to see if there is any force air cooling (ie., n internal fan)/ i don't recall seeing one.

[Roger Frazee]

It's good that it has internal overload, if that is working properly the motor will open the winding at the thermal heat setting. Of course a good sharp blade is essential for good performance as you are aware. If your not tripping the thermal overload I would suspect your fine and the motor is not overly hot.