[svoboda]

I run into this question at a friends house... The jointer and tablesaw are now running on 220 volts... It at one time was wired for 110 volts... Someone converted these duel motors over to 220... but... are only using 2 wire operation... First of all I'm sure this is unsafe and my question is... Do these motors need the third ground wire.. neutral... to run efficient... and please explain to me the loop taken by a 220 volt motor...

[Stratmando]

Dual voltage motors have at least 4 wires for swapping voltages. There is usually diagram on connection cover or motor. If wired for 120 volts, 1 wire will be the neutral, if wired for 240volts there is no neutral.
The ground is not necessay to opperate, it is ti keep motor at ground potential, if a wire breaks free, case will not become live and a shock hazzard, it should trip breaker.

[KISS]

Strat:

I don't like the way you phrased the answer.

Ground is required by the NEC. It does not carry current. It will operate without it, but it won't be safe. It prevents the saw from being energised at a voltage potential with respect to ground.

The way the use does 240, 220 doesn't exist anymore is that the transformer that supplies the premises grounds the center tap. Thus you get two 120 V AC circuits that are 180 degrees out of phase with the center tap.

Safety issues require that both poles be broken at the panel board when there is a fault on one of the 120 V legs.

The Saw sees 240 to it's motor, but 120 is seen from one leg to ground and the other leg to ground.

0 volts is seen from the neutral to ground. They are connected at ONE POINT in the service.

Thus if one siide of the 240 accidentally touced ground and table saw was not properly grounded, there would be 120 V between the table saw and ground.

This is obviously safer than 240 V with respect to ground.

Not all countries have this system.

It's called single phase. The distribution is single phase (primary voltage). True Two phase did exist in the US.

The loop is SAW - circuit breaker - side A - 240 xformer - circuit breaker - side B - and back to saw.

Neutral is provided to some controls and systems that require some 120 V.

Under a fault condition, some portion of the motor winding touches ground. If it was midway, it would be 120V with respect to ground. This will trip the breaker.

If that ground was not present, the current might go through you. Depending on where it entered and exited, you could be in trouble. Only a few milliamperes across the heart muscle is enough to disrupt the heart. That's the purpose of GFCI's. It measures this imbalance and shuts off the device.

240 is a good thing. Less wear and tear on the swiches (lower current) and lower wiring costs.