AndrewV wrote:

I picked up a table saw(very large cast iron top) 5 hp single ph motor, has
a magnetic switch on it . It will run only when you hold in the start
button, shuts down as soon as you let go, tough to use that way... I
cleaned out the switch and box, checked for loose wires, found no arced or
burnt contacts , no difference. I have my trusty multi-meter and am ready to
troubleshoot as soon as one of the RCM electrical guru's rains a bit of
knowledge on me. What do I do next?

Thanks

Andrew


Since the motor starts when you push in the start switch the start
switch is wired directly to the coil. There is a hold circuit that
keeps the coil energized when you release the start switch. This
circuit consists of usually two devices, an aux set of contacts on the
contactor and a stop switch. The stop switch is a normally closed set
of contacts. These are wired in series. Once the aux contacts are
engaged the curent travels through the stop switch and the aux contacts
which are closed when the coil is pulling them in. If you hit the stop
switch it opens the circuit and the contacts drop out, turning off the
saw.

Sometimes they wire the stop switch in series with the start switch but
not in your case. The aux contacts are always across the start switch.


John