View Full Version : OT - Circuit Breakers

10-19-2014, 01:03 PM
Wife and I took about a ten day road trip and got back home a few days ago. Before leaving I turned off both the upstairs and downstairs Heating/AC units at the thermostats.

While we were gone this area had some very severe electrical storms. We returned to find that after turning it back on, the upstairs unit is not working. After poking around I found a 50 amp circuit breaker at the main service panel was in a kind of semi-tripped state, i.e. halfway between tripped and engaged. The first few attempts to reset it would not hold. Eventually after turning the AC unit off and waiting awhile I did get it reset to the engaged position. But the AC is still not working.

My question: Is it likely that that breaker (it's actually two breakers clipped together) is now kaput, and that's my problem? I hate to call the AC repair folks if it's just a matter of a bad breaker.

Also, while I have installed breakers (tho it's been a few years), I've never pulled one out. What does that entail?

Jon Heron
10-19-2014, 01:15 PM
When its in the middle position it has tripped. After you reset it does it trip again or will it just not reset at all?
If it resets fine then trips shortly after you likely need to service your AC unit.
Circuit breakers do go bad but you didnt provide enough info for us to say if its the breaker or not....

10-19-2014, 01:20 PM
Easy to change the breaker. Turn off main service breaker, remove pannel cover, this will allow you to pull old breaker out and replace it.

10-19-2014, 01:44 PM
Breakers do fail but rarely like that, there is probably an overload in the compressor unit. Stop reseting it or you might do more damage.

10-19-2014, 01:59 PM
...... After you reset it does it trip again or will it just not reset at all?
If it resets fine then trips shortly after you likely need to service your AC unit.
Circuit breakers do go bad but you didnt provide enough info for us to say if its the breaker or not....

The first few tries it simply would not reset. ...even after I first flipped it back to the fully tripped position. When I would push it to the engaged position I would feel no click, just a spring pressure that would immediately return it to that middle position.
As I said, eventually it did reset, after I left it off awhile, under the assumption that maybe it need to cool (tho there was no evidence of heat).

10-19-2014, 02:38 PM
When a breaker trips, it goes to a midpoint position (so you know that it has tripped and not just been turned off). To reset it you must flip it to the off position before returning it to on. That probably accounts for your first attempts not "holding". And as others have said, while breakers do go bad, its not likely in your situation. I'd recommend -

1) Set the breaker to off.
2) Check the AC/Heater for its own breaker. Reset it.
3) Turn the breaker back on.

If the unit doesn't fire up or the breaker trips again, you'll need to schedule a service call.

10-19-2014, 03:16 PM
Got a multimeter? I'd suggest some basic troubleshooting (ie. see if you have power at the a/c unit) before deeming it is/isnt the breaker.

Not sure about others experience, but given a lightning storm I wouldnt be surprised if the breaker was bad bc Ive seen it happen several times.

10-19-2014, 05:12 PM
Turn the breaker off, remove the wires. Turn it back on. If it doesn't trip with no load it probably isn't bad. Turn it off again,put the wire back on. If it trips you probably have problem with the AC. If it trips instantly there is likely a short somewhere. If it trips after a fair number of seconds then it is likely a compressor problem.

Paul Alciatore
10-19-2014, 05:36 PM
If you have a multimeter, you can read the output Voltage on the breaker by probing the two screws that secure the wires in the breaker. It should read 220 to 250 Volts: be sure to preset the meter to a 250 to 1000 Volt AC scale BEFORE testing. And be careful.

If no Voltage in the reset position, replace the breaker.

ACs often have internal breakers. They may be obvious or just a little button on the compressor. It probably won't hurt too much to try resetting one if you can find it.

If you are still unsure, replacing the breaker (in the box) is probably the least expensive thing you can try. Have someone with you with a flashlight (and an insulated rope). Turn the main OFF and turn that breaker OFF. Remove the wires from the breaker and then remove it (they usually lift on the terminal end). Reverse the movement to install the new one and connect the wires as they were.

Unfortunately, breakers are rarely the problem. They usually run for years and decades with no problems. It is far more likely that a lightning strike effected your AC unit.

On that insulated rope: under NO circumstances should your assistant try to grab you if you are being shocked and can't get free. They should ONLY use the rope or other insulated means of yanking you from the conductor(s). Probably best to tie the rope around your waste before starting.

Mike Nash
10-19-2014, 05:55 PM
It occurs to me that there is usually a fuse, breaker or disconnect of some type in a box outside near the AC unit. If it was a windy, rainy storm and that got wet inside it could have carbon tracked there causing your indoor breaker to trip.

A coworker's ground fault breaker (Nema 3R breaker panel outside) got wet and failed after that last big storm that came through this past week.

10-19-2014, 07:38 PM
The circuit breaker outside is in a well protected box on what's normally the lee side of the house, surrounded by a fence, the AC unit, and a chimney. It was bone dry when I opened it. ...and of course the breaker at the unit in the attic is totally out of the weather.
Both were untripped and could be tripped then reset as normal.

I think I'll just wait and call for service

10-19-2014, 08:03 PM
I have designed and built circuit breaker test equipment, but mostly for much larger industrial breakers 100-4000 amps and 480-600 VAC. They are tested by injecting a high current at low voltage and measuring how long they take to trip at known currents, usually 3x for time delay (a 20 amp breaker carrying 60 amps may take 10-90 seconds to trip), and then up to 15x to determine where they trip instantaneously.

A simple "redneck" tester can be rigged up with a loop of wire from a soldering gun, or you could use a welder (although it's not good to put DC through an AC rated breaker). You might be able to use a spot welder, especially the home-made type that use a microwave oven transformer rewound with a few turns of heavy wire.

Circuit breakers can and do fail, and you are lucky if it fails open. The best protection is a fuse. It is a good idea to cycle all the breakers manually once a year or so to free up the mechanism and make sure they still break and make the circuit. Some brands are much better than others. It is always best to check them electrically by primary injection, and industrial breakers are also usually opened to clean the contacts and lubricate the mechanisms, and a final test involves insulation testing between poles and across the contacts, typically at 1500-2500 VDC or AC.

If you aren't sure of what you are doing, it's best to call in a pro.