On 2014-01-12, DaveC wrote:
A friend (in USA) with a 220v, 1-phase horizontal bandsaw in his home machine
shop wants to replace the 1/4 hp motor with 1/2 hp and rewire with an
auto-off switch (when the blade cuts through the metal).

I always default to using a 3-wire control with contactor, but he asks the
logical question: "Why?"

Other than the "If the power fails while cutting" answer (which he says seems
of limited additional value on a saw with auto-stop feature) I wasn't very
convincing.

What are the arguments for using a contactor as opposed to a simple on-off
switch of equivalent rating?

Mostly -- the contactor would (or should, if wired correctly)
break power to both sides of the motor. And -- he can use a lighter
duty switch for the "cut complete" switch, so the weight of the arm
would be more likely to trip it. A heavy duty switch capable of
handling the current of a 1/2 HP motor, and switching both sides of the
240 VAC feed might take too much operating force.

Also -- the "cut complete" switch can be a momentary contact
one, so you lift the arm, reposition the stock for the next cut, let the
blade down in contact with the workpiece, and push a button more
conveniently located to re-start the motor.

*And* -- a mushroom switch can be conveniently located to power
the motor down if it starts spitting smoke. :-)

Enjoy,
DoN.

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