Thread: Electricians! I need guidance!

I got this grinder (2007 Delta one speed,1/3 HP) for five bucks, so it'll be replacing the treadle grinder as soon as I figure where to put it. But what's this box they've got attached to it? I get that it's some sort of redundant safety mechanism(lockout/tagout), but is that all? It makes a pretty loud humming noise when I flip the switch.

I'm not an electrician, but it looks like a starter. It provides a set of contacts for the motor and thermal overload protection. Made by Furnas correct? Look it up on their website. Furnas Controls | Motor Starters, Contactors and Pushbuttons

Capacitor?

I'm not an electrician....but I do have one on staff......
In the diagram....
T= terminal, as in connection point
L= inductor or coil.
The idea behind the starter box is that you use a small voltage (110-120 vac) to pull in some contacts ( think really big relay ) to pass the larger voltage through to run the motor ( think 480 vac multi phase.) The starter box is usually used for motors much larger than 1/3 hp. Smaller motors tend to have the starter capacitors and thermal overloads built into them. The box is a bit overkill IMHO. The humming noise is the sound of the coil holding in the contactor. If it works run with it, it adds a layer of protection to your grinder.

Thanks so much! I was hoping I wouldn't have to remove it. Good bye weeks and weeks of handsanding! Goodbye treadle grinder! Hello, potential loss of limbs, and emergency surgical situations! Guess it's time to buy that leather apron and some steel toes.

You've got a motor starter for sure. Serious overkill. There's an electromagnet that closes the circuit when you push Start an holds it closed until you hit Stop. As explained above, usually the electromagnet operates at a lower voltage than does the motor itself, so it's a sort of remote control that distances you from the higher voltage (and, more importantly, the larger current) that runs the motor. In addition, there is a thermal overload protection that cuts power to the motor before the motor's windings get too hot. At excessive temps the winding insulation degrades and, at the mild end, performance declines. Further degradation leads to a flat-out short circuit, which will trip your breaker.

I've only seen that kind of protection on industrial motors.

The circuit breaker in your house's panel prevents your house's wiring from overheating caused by short circuits or overloads that draw more current than the wire is sized for. The motor starter's thermal overload feature protects the motor windings from overheating caused by bad bearings, continuous heavy use, or mechanical jamups in whatever the motor is driving. A motor that is prevented from turning is basically a very expensive and short-lived space heater.