Right now we build our pump control circuits with a branch circuit breaker, into a contactor, into an overload relay, then to the motor. We currently take an aux contact reading from the contactor to show the pump is on, but if the circuit breaker trips, or indication is still showing the pump on, when it is not. I know I could use a relay in parallel with the motor wires but seems excessive to use a 480v relay just for the signal? Example: 480V, 3Ph, 60hz motor. Does a manual motor starter have a contact usually to do this?

Thanks for the help.

 

the normal way this is handled is by opening the power to the contactor coil if the CB trips. this is done either by powering the control circuit up with a transformer that is downstream of the circuit breaker or via an aux contact off the CB.

--
Bob
http://ilbob.blogspot.com/

 

A pressure switch could be used in series with the aux contact to indicate the pump is producing pressure.

Or a speed switch.

 

This can be achieved in multiple ways.

I guess you are already reading the Ampere load to the motor.

As the current is negligible when the motor trips, you can make a logic added to the HMI to measure a Low Low alarm when the signal for Pump On is present. (Cheapest and most reliable)

MSRBs can be used as well.

 

Feed the contactor coil from downstream of the circuit breaker just like they have been doing for the last 100 years.

The circuit breaker trips and the contactor drops out along with the RUN contact.

 

Roy,

Wasn't something like this involved in the 3-Mile Island catastrophe?

Phil.

 

It was a solenoid valve indication with the open/closed indication being only coil voltage while the valve was stuck open. Thus very similar.

Since using TMI lessons learned, the other contributing factor was the isolated discharge of the 3 aux feedwater pumps. So for a critical "pump running" indication, a pressure or flow validation versus just motor supplied voltage.

I recall the old operator boards having the green/red power status above the control switch with a blue "pump pressure" status lamp between those two.

>Wasn't something like this involved in the 3-Mile Island catastrophe?