On Fri, 22 Apr 2005 12:02:27 GMT, "Karl Townsend"
remove .NOT to reply wrote:

...
(If you want double insurance on 3-Phase you can hook a simple $20
electronic phase monitor up after the starter contactor, which will
detect a dropped phase, rotation reversal, or big voltage imbalance
and open the contactor even before the overload heaters do, in well
under a second. Cheap insurance.)
...

Here's something I hadn't heard of. Are they readily available from a place
like Grainger or McMasterCarr?

Grainger carries the Square-D starters with Motor Logic (tm)
electronic overload, which has a phase monitor built in. (Cat 395 PP
369) This will catch any possible failure mode I can think of.

ICM makes separate wire in phase monitors.

Would it be a good idea to wire one of these into the Estop circuit on large
machines? If this device drops, open a NC contact in front of MCR? (Master
Control Relay)

I had a weird one where my generated leg dropped out after my hydraulic pump
started on my huge CNC lathe. (pump comes in on Estop reset) The pump kept
going on two legs (as all three phase motors will) until I tried to bring in
my 20 hp spindle. It popped the main circuit breaker in the machine. No big
deal, but this means the control lost power also.

If you're talking a manufactured leg from a phase converter, you are
probably better off with a plain old starter with three heaters. Or a
phase monitor that can be adjusted to rather wide tolerances of "OK".

The voltage on the manufactured leg is probably going to vary enough
to drive an electronic monitor nuts - it's expecting to see nice clean
and rock steady utility-fed 3-phase that doesn't vary more than a few
volts, at worst a motor generator plant...

And yes, you could tap into the control loop of any motor starter
and have it drop out the main control power to the equipment - hell,
you can do about anything with relays. Give me 10,000 relays (and a
few other critical components), and I can build you a complete
telephone exchange switch. One that will take a whole lot of daily
maintenance to keep running, but they worked for 75 years...

-- Bruce --
--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
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