50-Amp AC Breaker Keeps Tripping

Circuit breakers wear out. If the current is close to the CB rating or if loads from a motor momentarily exceeds the CB rating on starting, this shortens it's life. Replacing it with a larger breaker is not a good idea unless the wire is large enough to handle that current. The breaker is on a 220 V circuit right! A 2-pole breaker should be powering only 220 V appliances. If you are tapping 110 V off the 220, you may be creating an imbalance that causes a higher voltage in one leg and a lower voltage in the other leg.

Also check the specifications on your air conditioner. If the label is worn off, you might be able to look it up on the manufacturer's web site. There should be a maximum breaker size specified, and you shouldn't exceed that even if the wiring can handle more current. If the breaker is tripping, but seems to be the correct size for the A/C unit, either the breaker or the air conditioner is worn out.

Have the same problem on a chiller (50 A class C MCB of its compressor) - suspect supply voltage at nights 1. goes up, or 2. goes down. Also, may be a bad contact somewhere in the contactor coil's circuit making the contactor pulsate frantically leading to the MCB's trip.

I just did it today, the loads variate in each face 16 to 17 amps, it's a 50 amp breaker. It trips every 3 to 5 days, I don't believe its the breaker I've had issues with breakers of this kind only 3 times, and they usually trip in a very short period of time after being turned on. In this case it takes days, also, there are no junction boxes in between the run, it's straight cable with no splices in between. I'm guessing something could be wrong with the AC unit, or roof top UNIT.

*PHASE

Well, find out. Get a megger and test it, just to be sure.

what i understand from this discussion that either to check the total current or increase it by 125% but make sure that it is less then the 80% capacity of the cable ....

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You could also rent a line analyzer/plotter that will plot voltage and current over time. Usually available at an electrical supply house in your vicinity.

Just another avenue to explore.

Have seen the same problem befor. you need to change the breaker to a new 50amp and then instal a soft start kit on the compressor. some times when the compressor starts under high head pressure it will cause the breaker to trip. the soft start kit will stop this problem.

I recommend that you diagnose the problem before taking corrective action.

Yes, increasing the breaker size might cause the breaker tripping to cease for a while, but if you have only masked over a developing problem, you may have only succeeded in delaying what will become a much bigger and expensive repair when the problem fully develops.

You have been presented an opportunity to prevent a larger problem, sort of like a doctor that catches cancer in the early stages from a few small indicators, and rather than prescribe a pain killer to mask the symptoms, he sends the patient in for a few tests.

Some of the available methods have been suggested. I also recommend a thermal imaging camera, or in the least a non-contact thermometer (much less expensive).

From the evidence, it seems you are dealing with an overload that requires time to build up sufficient thermal action in the breaker, so you could periodically check the breaker temperature. Also, in the few minutes immediately following a breaker trip, you can check for excessive heat in the major devices, motors, compressors, controllers and switches etc.

Shade tree (back-yard) mechanics change out parts by pure guess until the problem goes away. Professional mechanics let the diagnostic tools do the guessing for them.

Regards, CJM

naviero1 - I don't know if you fixed problem yet, but, will post anyway. I noticed you are from Lost Wages where it is still possibly very warm. Please use the simple approach first, before you redesign the system. The condenser could be dirty enough to raise the amperage. If single phase, capacitor could be bad slowing fan down. Bearings in fan motor could be starting to wear (raising amps & discharge temperature). See what i mean? More than likely the breaker was installed per design along with wire sizing. Though i have seen electricians cut corners and/or engineers not considering Nevada temps in design, etc.

Yeah, it could be, right now I have an AC tech checking his equipment, I'm in charge mainly of the electrical systems before the AC. It's a straight run with no splices in between the breaker, which is a 3 pole 50 amp, and the breaker at the AC unit. I've had really good answer pointing that it could be the breaker itself, I'm not quiet sure yet.

One other thing I would check; is the breaker commercial or consumer grade? I believe there is a difference in the cycle life. A mil-spec device will last much longer than a consumer device. Take wall switches or receptacles for example. You can buy one for 29¢ or $5.

Replace it like-for-like. Destroy the old one; it's knackered.