Breaker Did not trip.

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hde_electric

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I went out on a service call to try to fix some lights that were not working and after checking them found out the Switch Leg was making contact with the grounding conductor but the breaker would not trip and all you would hear was a hum noise in the panel. Can somebody give some input on what was happening? The voltage was 120 Volts and the panel Was Cutler-Hammer Type CH.
 
Re: Breaker Did not trip.

Defective CB or

High resistance ground putting the circuit breaker into a long time operation in lieu of instaneous trip.

Replace CB..Test existing CB and verify equipment ground in intact.

Did you measure the current on the line conductor?
 
Re: Breaker Did not trip.

This seem's common when there is a long circuit run. I have a load tester that will place about 30 amp's on a 20 amp breaker or 25 amps on a 15 amp breaker and I have had very few breaker not trip when I connect the tester to the breaker but when I connect it to a circuit with a long run it has taken longer than it should. so voltage drop can be important. Actually it is the resistance of the circuit that will limit the current as resistance is current limiting.
 
Re: Breaker Did not trip.

I have had very few breakers go bad, I would say from what I have seen it is a rare occasion. I think its along the lines that if the breaker trips its a bad breaker, rather than finding the problem. The ones that have been bad were due to overheating, " It kept tripping so I kept resetting it, I had to put someone by the panel to keep resetting it, till it wouldn't reset anymore"
 
Re: Breaker Did not trip.

Hurk:

How long is it taking you to trip a 20 amp CB at 30 amps? In addition the voltage drop at a distance with the device you have will affect the current and therefore the time to trip the CB
 
Re: Breaker Did not trip.

NEMA AB4, Guidelines for Inspection and Preventive Maintenance of Molded case Circuit Breakers Used in Commercial and Industrial Applications, Table 5-3, Values for Inverse Time Trip test, states that the maximum trip tome in seconds for breakers of a continuous current rating of 0-30a up to 250v shall be 50sec at 300% of Rated current of the circuit breaker.
It would take a 20a breaker with a 30a load significantly longer. Just for grins I dug out a trip curve for a single pole breaker for frames less than 50a. At 150% of its rated current the minimum trip time was about 1 min. and a maximum of 25-30 min which may raise an few eyebrows. I could understand that but most are familiar with published breaker trip curves and what they mean.
Another thing that has a huge affect of breaker trip times is ambient temperature. Sense it is not uncommon for a panel to be located in a cool basement this would add to the trip time. Warmer ambient temperature would be less.
 
Re: Breaker Did not trip.

Originally posted by hde_electric:
I went out on a service call to try to fix some lights that were not working and after checking them found out the Switch Leg was making contact with the grounding conductor but the breaker would not trip and all you would hear was a hum noise in the panel. Can somebody give some input on what was happening? The voltage was 120 Volts and the panel Was Cutler-Hammer Type CH.
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Was it the in or out of the switch? If it was the out, how long did you leave it in the "on" position to test it? Or was it just flipping it up, seeing no light, flipping it down again type thing?
 
Re: Breaker Did not trip.

I would speculate that there is a problem with the grounding of the system. Try reading voltage between "hot" leg and ground then "hot" leg and grounded (neutral) conductor.
 
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