Originally Posted by oldsewnsew

Here's another "dim bulb" piece of test gear from the days when I tinkered with old tube radios and hi-fi's.
It is a short circuit detector, that limits the current. It will also slow down a motor, it's not the same principle as a rheostat because almost full line voltage is still across the motor. This is actually a receptacle that came with a socket for one of the old screw in glass fuses. A bulb will light when the motors plugged into it. A motor has almost no resistance unless there is an open in the wiring somewhere. But the circuit breaker for that wall won't trip, even if there's a short, because the bulb limits current, a 1 amp motor, (around 100 watts give or take) with a 100 Watt bulb screwed in, will run about full speed. If you try to stop the motor, the bulb (which was kind of dim) will start to get brighter because the load is increasing.
Again, my caveat is don't get too wild with this stuff, don't do it on a wet basement floor, etc, etc etc...
[ATTACH=CONFIG]471704[/ATTACH] In the first photo, the test box is plugged in, but the motor isn't. Next photo, the motor is plugged in and running [ATTACH=CONFIG]471705[/ATTACH] I think that was a 75W bulb, motor was about 80% of full speed, next photo 100W bulb, brighter, and motor going almost full speed.
[ATTACH=CONFIG]471706[/ATTACH]Please excuse the bare ugly vise jaws on the motor, normally I'd cushion it with something. You may wonder why I did this...dunno just to see what would happen I guess.