On Jul 31, 10:50*pm, Gunner Asch wrote:
On Sat, 31 Jul 2010 11:47:07 -0700, "Ivan Vegvary"

wrote:

Of course mine comes in a metal mounting box with appropriate lock-outs.
Iggy, there's all sorts of literature about 'heaters'. *I have no idea about
what they speak.

"heaters" are mica posts wound with resistance wire. *They are in series
with the wire feeding each phase input...IE there are 3 of them and the
motor wiring goes through them from the power supply.

When any one of them draws too much power..they heat up and cause a
bimetal switch to open up, stopping power to the motor.

Its a "fuse", but one that is resettable. Think of it as a circuit
breaker..which indeed it is. *Some "heaters" are replaceable with
smaller or larger values so if you need to have it trip at less amps,
you use a smaller set, or at more amps..a larger set.

The contactor I have on my Harrison L5 has three 'heaters' one on each
phase, these each heat their own bi-metal strip that moves a bar, the
bar is attached to a cam which then moves a (spring loaded) lever off
from a contact, the power to the electromagnet is through that contact
so when the bar moves enough, power to the electromagnet is cut and
the machine shuts down. As soon as the bi-metal cools it 'resets' and
the machine can be turned on again.

It can be adjusted from IIRC 10A down to 0.3A by moving a lever
attached to the cam.

Very simple and hardly anything to go wrong.

Very simple, nearly universal in use in virtually all "heavy" machinery.

and they have been in use for at least 60-70 years too, I'm pretty
sure mine was original equipment on a lathe which was made in the
40's.
Even though I've converted to a new motor with a VFD I've kept the
contactor (although I replaced the (few) pieces of wiring in mine as a
piece of mind measure), works perfectly fine with just single rather
than 3 phase too!

Druid