Main is tripping?

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jerryb52

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Lake Worth, Florida
This is my first post and not sure if this is the correct place for it.
The main at my house just tripped. The A/C has been acting up and the landlord had a tech look at it a few days ago and he said it was okay. I went out and re-set the main and noticed that the two pole 50 for the A/C was also tripped.

I do mostly new commercial work and don't know much about service work. Can anyone tell me what may be the problem? The panel is an old ITE 200A.
Thanks.
 
Re: Main is tripping?

I recently ran into this problem at a bank here in town. As I learned through this forum, many of the newer air conditioning condensers out there have a start-up current of almost 180 amps for approximately 1 second or so. If, for some reason that unit malfunctions or has reason to draw that current for a longer period of time it will not only trip the 2-pole 50 amp breaker but the 200 amp main also.

Phil,
Gold Star Electric
 
Re: Main is tripping?

Your compressor motor may pull many times it's running load at start-up, hence the breaker sizing tables for motors in Art.450.

If this is a recent problem with existing equipment, a hard-start kit (commercially, Super-Boost) may alleviate the problem. However I would pull the breakers in question and inspect for burnt lugs, also cheak for V. leak with the breaker off and replace any damaged equipment.

I'd meg down the motor as well when you have a little light to do it by, and inspect the wiring at the unit for faults.
 
Re: Main is tripping?

"Breaker tripping" is a bit ambiguous. Is the breaker tripping because of an overload, i.e. thermal trip or instantaneous, i.e.' magnetic trip?
Without having a recording instrument which is set up to capture the event which causes the breaker to trip it can be difficult to determine.
A breaker that trips thermally because of an overload commonly can not be reset (latched) and closed until the thermal element cools off. A breaker that trips magnetically can be reset and closed immediately after a trip. A breaker that trips magnetically means that it has been subjected to fault current. Small residential breakers commonly have a magnetic trip value of around 6-7x the breaker rating where most larger breakers will be 10x.
Fault currents as a result of a faulted circuit can be easily be as high as the available fault current at the service entrance. What this means is that if there is a fault in a branch circuit both the branch breaker which is supposed to protect that circuit as will as the main breaker will see the same fault current an there will be a race to see which one will trip and clear the fault. Often times it's the main breaker. Remember that there is no time delay when it comes to the magnetic trip element.
With
I personally would consider an intermittent fault since the main is tripping what I understand to be something that is "acting up."
It is highly unlikely that the main would trip thermally before the branch breaker unless the main is significantly loaded be other circuits to beguine with.
 
Re: Main is tripping?

JerryB52,those old ITE Quad breakers get allot of corrosion were they contact the panel busses.Check that out. ;)
 
Re: Main is tripping?

I would first feel the panel for heat,then pop every breaker 1 at a time and inspect bus bar.Also tighten all screws ,both hots and neutrals and lugs to main breaker.If they are quad mains there is a chance 1 of the 100 amps are bad 2x 100=200 i hate them kind of breakers.
A hard start cap might help on the ac comp.
Also check each breaker for corrosion,any bad connections any place cause heat and will trip the main

[ October 06, 2004, 05:36 AM: Message edited by: jimwalker ]
 
Re: Main is tripping?

Originally posted by jerryb52:
This is my first post and not sure if this is the correct place for it.
The main at my house just tripped. The A/C has been acting up and the landlord had a tech look at it a few days ago and he said it was okay. I went out and re-set the main and noticed that the two pole 50 for the A/C was also tripped.

I do mostly new commercial work and don't know much about service work. Can anyone tell me what may be the problem? The panel is an old ITE 200A.
Thanks.
Click to expand...
You might want to look at a couple of things.

Does the thing trip instantly when the AC goes on or does it take some time?

Since both the main and the 50A CB were tripped it seems likely that a lot of current is flowing and. Could be a motor problem (intermittant winding short or something).
 
Re: Main is tripping?

Check the AIC rating on the 2 breakers.

The Main may be more sensitive than the branch circuit breaker..
 
Re: Main is tripping?

There may be a misconception of a breaker's AIC rating. AIC rating doesn't have anything to do with the breaker tripping other than its ability to clear a fault without destroying itself. For example breakers with a 20at rating with the same magnetic trip calibration lets say 6 x its rating or 120a (usually the magnetic trip calibration tolerance is +-20%), will all trip at the same fault current if the fault were 120a or above, even is their kaic rating are 10, 22,25,65, (even 100kaic if this breaker rating is available in that frame size) etc. However, the fault current may be as much as the available fault current such as subjecting a 10kaic rated breaker to a 20kaic fault a 20at, 10kaic rated breaker will trip but with almost all certainty will sustain damage and may be blown appart where a 20at breaker with a 22kaic will clear the fault without damage, surviving to do it again.
 
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