contactors and transformers

[captain117]

This may be a dumb question but here goes anyway. Recently I installed a series of lighting circuits in a building hallway. The whole thing uses four circuits, all 20 amp. The first is a control circuit, so the owners could turn ALL lights on with one switch. This circuit powers three contactors, which are all on their own breaker. The second circuit is energizing a contactor which powers a row of incandescent lights. The third circuit energizes a contactor which powers two trac lighting transformers. The fourth circuit energizes a contactor which powers two trac lighting transformers.
One of the pairs of trac light track transformers has a total load of 10 12v 20w bulbs, and the other pair has 13 12v 20w bulbs. The problem is every once in a while one of the trac light breakers trip, I cannot seem to come up with any pattern for it. They always seem to trip either just before being turned on or while off, never while on. I have tried new breakers and checked amps at the breaker, the highest was 2.9 amps. Any help would be appreciated.

 

[bphgravity]

Re: contactors and transformers

Breakers trip for only two conditions, overloads and overcurrents. (with the exception of manufacturer defect) Obviously you do not have any overload condition if the breaker trips with no load. Overcurrents are due to ground-faults or short circuits.

Have you performed any type of insulation tests to detertmine if there are any inadvertent ground-faults or shorts?

What is the rating of the transformer?

 

[petersonra]

Re: contactors and transformers

Originally posted by captain117:
They always seem to trip either just before being turned on or while off, never while on. I have tried new breakers and checked amps at the breaker, the highest was 2.9 amps. Any help would be appreciated.

If the contactors supplying these xfmrs are off, I don't see how the xfmrs could possibly be causing the problem since there would be no electrical circuit from the breaker to the xfmr.

I'd be looking for some kind of intermittant ground fault in your wiring between the breaker and the contactor.