Why does my main AC breaker keep tripping?

[Toubab]

Originally Posted by hellosailor

"So can/should I just put in a larger breaker?"
No offense meant, but if you can ask that, you might want to call an electrician.

A breaker trips either because it is defective (they do wear out, they do not last forever) or because it is trying to protect you from dying in an electrical fire. They never, ever, trip "at random".

No offense taken, for sure. This is actually what I thought, but my dad, who's usually more knowledgeable about these things, was thinking it might be possible to put a larger breaker. I think it's very likely that the breaker is just wearing out. It's likely original and the boat was built in 1991.

Originally Posted by transmitterdan

Toubab,

You have received some good advice so far.

Does the breaker trip when the air conditioner starts or does it trip after it has been running for a while?

What is the line voltage at your breaker when the A/C is running?

What is the current through the breaker when the A/C is running?

An inexpensive clamp meter can be used to measure voltage and current. If all this is gibberish then pay an electrician to look over your setup. It could be money well spent.

It trips after the air conditioner has been running for awhile. I don't ever remember it tripping as soon as the AC turned on. It seems to happen more over the summer too, when the AC is running all the time so it shouldn't be turning off and on when I'm gone but I'll often come home to the breaker being tripped.

I haven't measured the currents yet but I just got a snazzy new clamp-on meter so I'll see what I can find and report back.

Thanks everyone!

[Cheechako]

Originally Posted by Paul Elliott

Sometimes breakers just go bad -- they trip for no good reason, well under their rated current. You should measure the current you are actually drawing to make sure that you don't have a fault somewhere. If everything looks good, they try replacing the breaker with a new, properly-sized one.

Yep They just start breaking at low load sometimes. If you arent overloading, I would try a new one.

[CaptFrankM]

These symptoms sound very similar to the ones I had last summer. When you check the current flow, leave the meter on the line and watch the amperage over time. Mine would start at about ten amps, and slowly rise to fifteen amps, which would trip the breaker. At the same time, the voltage would slowly drop from 115 volts to about 109.

That's why I recommended installing a? permanent AC electrical monitor, by the way. Sometimes, it helps to know what both volts and amps are doing.

As for what my problem was - bad wiring on the pier and bad cooling water. Once I changed marinas, my problems all resolved.

[transmitterdan]

Tripping after running a while can be a weak breaker. It's easy to replace the breaker. But before replacing look carefully at the wire terminals. If the wire terminations are not tight they can generate heat. The heat can cause the breaker to trip because most of these breakers use thermal trip mechanisms. If it looks good I would install a new same size breaker.

[hellosailor]

Toubab-
I'm going out on a limb and guessing the AC is not brand new either?

All AC systems eventually leak. Most are OK for 10 years or so and by 20 they've lost some gas. When that happens the compressor has to work harder and longer and then it draws more current, which is all you need to pop the breaker.

So, given that the breaker is OK until the AC has been running for a while, you might also want to put an ammeter on the AC circuit alone, and see how much that is drawing compared to the rating plate that is on the compressor. If the compressor says 15 amps but you see it is drawing 20...or even 17 during runs...you know you've got an AC problem. That might be the only problem, or just a coincidental problem, but it is worth checking out.

I'm also told there are two kinds of circuit breakers: The common cheap "thermal" breakers, where too much current causes them to overheat and trip, and a more expensive "magnetic" or "magnetodynamic" type, which throw when the increased current causes a higher magnetic field in the breaker. The magnetic type supposedly are way more expensive but last much longer. The thermal type have a definite number of trips in their life cycle, and then they need to be replaced.