Grounded Motor Windings

[Minuteman]

I replaced two Analog Intermatic time clocks with a Digital Intermatic timer for a customer today. The Main Pump and the Vac Pump on a 2P20 and the Hot Tub Pump on another 2P20. The timer has a temp probe to bring everything on to prevent freezing. All three have just one leg being opened through the timer.

As I tested everything, and the Hot Tub pump would run on 120v when the timer switch was open. The motor was shorted to ground but was not tripping the breaker. Even amped the ground wire and it was pulling 29 amps. Told the customer that the breakers should be GFCI and that he is lucky to still be here.

My question: Why didn't the breaker trip?

 

[don_resqcapt19]

How long does the motor run? Looking at the trip curve for one brand of breaker it shows a trip time of 35 to 500 seconds for a 29 amp load on a 20 amp breaker. If it is running longer than that, then either the breaker is bad, or it is not seeing all of that current. You said you checked the current on the ground wire, so it is possible there is a source for some of the current other than the motor. You need to check the current on the wires connected to the breaker.

 

[Minuteman]

Oh, I didn't let it run very long at all. He is going to get another motor and I will replace it. Also, I will install the GFCI's.

But thanks Don, I was thinking instantaneous trip because I saw it as a direct short.