Odd result.

[ptonsparky]

We are monitoring the current for Motor 1. Running, Max, and Minimum. We record the Max/Min after the motor has ran for 3 seconds.

Running is about 21 A with a no load condition. We have a broken belt minimum setting of 15 A which stops everything. Motor 2 starts when M1<22A for 15 seconds.

We were doing a final check out by moving grain today. Motor 2 had an auger that was frozen up which squealed some belts before we stopped it briefly and let it try to start again. The second attempt resulted in an alarm and shutdown caused by a "Broken Belt" alarm for current of 9 amps on M1.

We do not monitor M2, other than an N/O contact on the starter. The 4-20 ma cable for M1 is in a separate raceway from both motor feeders. We repeated the test with the same results then moved on to other issues. Could the LR of a small motor (7.5 to 10 hp, 3ph, 240v) result in enough VD to the power supply for the current transducer to cause this? We were not expecting this so had no VO
Ms connected.

 

[Julius Right]

The rated current will be 13.5-18 A and the starting current has to be 6-7 times for D.O.L. start and 1.5 times for VSD.
I don't know how your broken belt relay works [could be Under Current Relay?].However, I think you may delay the trip for more than 15 sec.[By the way, 15 sec starting time it seems to me to long]. You have to check the stall time [has to be, any way more than 15 sec.]- for D.O.L start.

 

[ptonsparky]

We monitor motor 1 current to detect a broken belt, overload, etc.

I should have stated "Motor 2 starts when M1 current is greater than 15 amps but less than 22A for 15 seconds."
There is no circumstance that the current is <=15, unless the belts or chains have broken, at which time all motors must stop.

FLA of Motor 1 is 50 amps.

The real question is how did the locked rotor of Motor 2 cause the monitoring equipment of Motor 1 to sense undercurrent when it was not under.

 

[kwired]

We monitor motor 1 current to detect a broken belt, overload, etc.

I should have stated "Motor 2 starts when M1 current is greater than 15 amps but less than 22A for 15 seconds."
There is no circumstance that the current is <=15, unless the belts or chains have broken, at which time all motors must stop.

FLA of Motor 1 is 50 amps.

The real question is how did the locked rotor of Motor 2 cause the monitoring equipment of Motor 1 to sense undercurrent when it was not under.

Is the source stout enough to sustain voltage with locked rotor in motor 2?

 

[ptonsparky]

Yes. More than adequate. I never noticed a flicker.