I was called out for a service call to a facility that has a septic tank with a 3-float control system with two pump motors. The above ground control box has the leads for 3-floats and 2 pump motors that come from the tank. The disconnect switch for each motor is a 1-pole 20 amp breaker. The call ticket said that one of the breakers keeps tripping. The motors are 120v.
When I got there the disconnect switch/breaker in the control box for motor 2 was tripped. I also noticed a separate test switch on the control panel for motor 2 that was in the "manual-on" position, while the test switch for motor 1 was in the "auto" position. I reset the disconnect switch/breaker to the on position. Since the test switch for motor 2 was in the "on" position the contactor for motor 2 pulled in and there was 120volts L-G at the terminals that feed motor 2. I couldn't hear the motor running, and put a clamp meter on the motor leads, which showed 0 amps. The disconnect switch/breaker held at this point, and didn't trip at all while I was doing any of the following testing.
When I turned the switch for motor 1 to the "on" position I could hear it running and read 6.5 amps with my clamp meter on the motor leads. After turning everything off I reversed the motor leads and got motor 1 to operate manually off either set of terminals, but motor 2 wouldn't run off either set of terminals. I tried ohming out the motor leads for motor 2; no continuity L-N, or L-G, but I got continuity N-G. I didn't know what to think about this so I did the same test on motor 1, which didn't show continuity L-N, L-G, or N-G.
At this point I'm making the assumption that since the motor 2 switch was in the "manual-on" position and that it was the "lag" motor (motor 1 is the "lead" motor) that it burned up since it was running constantly. I don't know how they are positioned in the tank in relation to each other. Does this sound plausible? Is there any other test I should have done? I did run enough water in the building to get the "lead" motor to start running and eventually get the alarm to go off, without getting motor 2 to start up.
Any feedback is appreciated.
Thanks,
Sky
When I got there the disconnect switch/breaker in the control box for motor 2 was tripped. I also noticed a separate test switch on the control panel for motor 2 that was in the "manual-on" position, while the test switch for motor 1 was in the "auto" position. I reset the disconnect switch/breaker to the on position. Since the test switch for motor 2 was in the "on" position the contactor for motor 2 pulled in and there was 120volts L-G at the terminals that feed motor 2. I couldn't hear the motor running, and put a clamp meter on the motor leads, which showed 0 amps. The disconnect switch/breaker held at this point, and didn't trip at all while I was doing any of the following testing.
When I turned the switch for motor 1 to the "on" position I could hear it running and read 6.5 amps with my clamp meter on the motor leads. After turning everything off I reversed the motor leads and got motor 1 to operate manually off either set of terminals, but motor 2 wouldn't run off either set of terminals. I tried ohming out the motor leads for motor 2; no continuity L-N, or L-G, but I got continuity N-G. I didn't know what to think about this so I did the same test on motor 1, which didn't show continuity L-N, L-G, or N-G.
At this point I'm making the assumption that since the motor 2 switch was in the "manual-on" position and that it was the "lag" motor (motor 1 is the "lead" motor) that it burned up since it was running constantly. I don't know how they are positioned in the tank in relation to each other. Does this sound plausible? Is there any other test I should have done? I did run enough water in the building to get the "lead" motor to start running and eventually get the alarm to go off, without getting motor 2 to start up.
Any feedback is appreciated.
Thanks,
Sky