a/c tripping main breaker to house?

Our ac unit is tripping the main breaker to our house. We bought the house in November and didn't jave any issues u til yesterday. The main breaker tripped yesterday. After flipping it back on, the ac ran for about 30 minutes and it tripped again so i turned the ac off at the 40 amp breaker and left it off until i got home from work today. Changed the air filter and cleaned the coils on the outside unit. Turned it on and after about 30 minutes it tripped the main breaker again. It is 88 degrees in the house. Anything i can do or do i need a new unit?

8 Answers

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  • 1 month ago

    Call an Electrican immediately as this could burn your home down. 

  • M.
    Lv 7
    1 month ago

    The 40 amp breaker to the A/C unit doesn't trip, but the 100 amp (?) MAIN breaker DOES trip?  Then the problem is likely inside your circuit breaker panel.

    Somebody with a clamp AC ammeter needs to do some checking in the circuit breaker panel. 

    Depending how things are wired and the actual current flowing, maybe the MAIN breaker has developed a problem. 

    Is your MAIN breaker 100 amps?  Or something else? 

    If more than 80 amps is flowing through it when it trips, it's just doing its job.  If less than 80 amps is flowing through it, then it may have become defective. 

    You need to know how much current is flowing through it.  

    Also, MAYBE one of the screws that clamps the input wiring is loose.  That would make heat and that heat could trip the MAIN breaker.  Be careful, the screws have live power on them.  Sometimes the screws require a hex key (Allen wrench) to tighten.  It must be insulated.

    Or maybe the (hopefully) copper bus bars that the MAIN breaker is snapped onto has oxidized and now heat is being generated at the contact point.  I'd also be measuring the voltage drop across the 2 contacts of the circuit breaker itself. 

    A trained person with a voltmeter and an ammeter can find the problem quickly. 

    If you have aluminum wiring or aluminum busbars in your circuit breaker panel, then some inspection is necessary.  Aluminum requires NOALOX compound on the connections.

    Is the body of the MAIN circuit breaker hot when your A/C is running for a while? 

    This kind of problem, if it's making heat because of contact resistance, is what causes house fires.  Don't play around.  Hire an expert to find and correct the problem right away. 

    You need to find the problem electrically, with a voltmeter or ammeter to identify the location of the problem.  Then fix the problem.  Then verify with the voltmeter or ammeter that the problem is gone.

  • JJ
    Lv 6
    1 month ago

    Not a problem with the unit. Likely a connection at the main getting hot causing the trip. You likely can't turn off power to the main...A good electrician can scan it to see if it is hot....

  • 1 month ago

    you need to call an a/c guy for detection/service.  the compressor in the outside unit MIGHT be the culprit ... BUT, it is also possible the control board has the indoor heat running out of season and the combination of the two is excessive current draw.  Compressors are replaceable, so is the exterior unit, without replacing the entire system.  you want to be sitting down when he presents his proposal ... it is virtually certain to exceed $1,000.  -- grampa

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  • 1 month ago

    It could be that your electrical service is just being overloaded. That's what it's acting like. If your main breaker is rated at 150 amps then you may be using more than 150 amps (actually maybe 80% of that - 120 amps).

    One test you can do is to turn off all other breakers and run the A/C. If no breakers trip then the panel is being overloaded when they are all on or the main breaker is getting weak.  If there is a problem with the A/C unit then the 40 amp breaker should trip, or the fuses in the disconnect near the unit outside, but not the main breaker during this test.

  • Anonymous
    1 month ago

    The fact that it's tripping the MAIN breaker and NOT the 40 amp breaker that it is wired to means that the MAIN breaker is most likely going bad. That's why you HAVE the 40 amp breaker in the first place. If the AC has trouble, the 40 will pop.  YOu need to have that main breaker looked at and replaced.  You will need an electrician to take care of this.  

  • martin
    Lv 7
    1 month ago

    See if anything else is running on the same local circuit with the AC.

  • 1 month ago

    Could be a faulty main breaker.  Especially  if it isn't tripping the breaker for the air conditioner. 

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