Motor current Monitor

I'm looking for a way to monitor motor current on a grinder (600 VAC 3Ph., 50 Hp) and provide an alarm and/or automatic shutdown on overload. It is a hand loaded plastic grinder, and our operators sometimes get overly enthusiastic (!) when feeding it.

Current/load display would also be desireable, if it doesn't significantly add to the price.

Any suggestions??

I have used a Tsubaki shock relay for a million years. Here's a link:

http://www.tsubaki.ca/pdfs/shockrelay.pdf

I specifically use the model TSB-SS-05, which is under $200.00 USD. There is another model with a built-in meter to watch where you're at current-wise.

In the past, I've had end-customers want to use the Allen-Bradley current sensing relay (bulletin 809S) and they found those to be very expensive (triple the cost of Tsubaki), non-linear and difficult when it comes to adjustment. The pot adjustments don't even have graduations! (sorry A-B on this one)

EDIT: I went back and checked out the Allen-Bradley 809S current monitor on their website. It appears that in the fifteen years since they turned me off (see above), they now make this unit with a keypad and display to adjust parameters. Outside of the price, this could be a viable option, if you like A-B.

Motor current is not the best way to monitor motor load. A lightly loaded motor and a properly loaded motor will draw close to the same amount of current. The lightly loaded motor operates at a lower power factor than the nominally loaded motor. As load increases, power factor increases towards unity, but the current draw of the motor changes very little.

These guys: http://www.loadcontrols.com/ make a device that monitors true load on the motor. I have used them in many applications, including monitoirng grinding wheel loading. They also have an article explaining reactive and active power in motors if you are not familiar with it.

+1 on load controls

Alaric said:

Motor current is not the best way to monitor motor load. ... These guys: http://www.loadcontrols.com/ make a device that monitors true load on the motor. ...

Click to expand...

Ditto on this recommendation. Just commissioned a facility with one of these and they work great. A little pricey but easy to change trip point on the fly and will work with different voltages which is one of my requirements in a test facility application: unit power can vary from 180V to 600V depending on the test du jour.