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Old 03-10-2013, 11:50   #1
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Why does my main AC breaker keep tripping?

I've got a 30 amp breaker for my main AC supply that runs my air conditioning, a few AC outlets, battery charger, and refrigeration. It will randomly trip pretty often. It does happen more often when I'm running more stuff but it also happens a lot when I'm just sleeping with the air conditioning on. I added the AC refrigeration since buying the boat but this was happening before that. I'm also planning on adding a second battery charger so I'm worried that I'm overloading the breaker.

So can/should I just put in a larger breaker? I don't think there's an actual short anywhere since sometimes I can go for days without it tripping.

Oh and I'm at a dock with shore power. I think it's only a 30 amp supply if that matters.

Thanks!
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Old 03-10-2013, 11:57   #2
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Re: Why does my main AC breaker keep tripping?

I did say inrush is tripping the breaker, It may have the wrong timing spec or the system could just be overloaded. Not much point raising the breaker rating if the dock doesnt support it , youll just trip breakers elsewhere,

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Old 03-10-2013, 12:01   #3
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Re: Why does my main AC breaker keep tripping?

I put in a seperate breaker panel for my A/C and heat. Now I have two 30 amp circuits from the dock. Haven't tripped a breaker since...LL
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Old 03-10-2013, 12:13   #4
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Re: Why does my main AC breaker keep tripping?

If you have a water heater on the 110V, Might want to only keep it on part time. Maybe an hour in the morning and an hour in the evening. Keeping the AC off for that time. Its the surge when the A/C and or fridge with waterheater and everything else running too causing it, most likely.

One other might be: Breakers will sometimes wear out and not latch right. There is a chance that installing a new 30 amp breaker would solve your issue.

OH, if there is excessive voltage drop in the shore cable and boat wiring, more amps will be pulled by motors and switching power supplies and that could cause the breaker to trip too. If you notice burn marks around the shore plugs (boat and dock) then at the minimum that plug needs to be changed for a new one..

Of course adding a second 110V panel for A/C is a really good idea too.
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Old 03-10-2013, 12:15   #5
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Re: Why does my main AC breaker keep tripping?

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.
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Old 03-10-2013, 12:26   #6
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Re: Why does my main AC breaker keep tripping?

You may well be using too much power on your system. AC and refrigeration are both big loads that draw significantly more current when the compressors kick in. Ideally, you would have someone competent to work on AC power put a clamp-on ammeter on the main circuit to see what it is drawing, especially when both compressors are running (perhaps turning them off for a few minutes then on at the same time). Remember that current in the milliamps can kill depending on path through the body and whether your skin is damp etc...
What can happen is that the breaker can hold when the compressors come on at different times, but when they come on at the exact same time, the inrush current is too much for the breaker to hold. Understand also that breakers will wear out eventually if they are tripping regularly. Please do not install a bigger breaker as it can become a fire hazard unless the panel and wiring is sized for it. Also any other loads of course contribute to the overall load on the main such as microwave ovens, the battery charger etc.
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Old 03-10-2013, 13:15   #7
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Re: Why does my main AC breaker keep tripping?

"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".

And, like fuses, you never want to just replace one with a higher rating. That's a good way to start a fire.

The odds are there is a dirty contact, or a problem with the shore power (low voltage perhaps) or something else simple that is tripping the breaker. But if you are not familiar with AC wiring, it isn't such a bad idea to call in an electrician, let them look over what you have, make suggestions for what needs replacing or upgrading, and giving the whole system a little TLC.

You need to find out what the dockside supply is, whether you have a GFI on the boat, the load capacities and ratings of all the equipment, and once you have all of that you can determine the least expensive way to get a truly safe and reliable system out of it.

You can certainly DIY on this, and there are a number of books and web sites to help. But calling in an electrician will certainly get you started faster and with more certainty about the result, even if you chose to DIY after getting his recommendations and any immediate repairs if necessary.
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Old 03-10-2013, 15:18   #8
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Re: Why does my main AC breaker keep tripping?

It sound like when the combination of all the electrical items happen at the same time there is a spike in amperage. The initial start up amp demand is higher than run amperage. So I have found the best is to install timers on the high amp items like the water heater, battery charger, heaters AC etc so the total amp demand does not exceed the breaker amperage. We had the same problem periodically so I installed timers on the water heater, one of the electric heater and AC so they could not turn on at the same time. The water heater turns on at 4:00 am till 6:00 AM.
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Old 03-10-2013, 15:54   #9
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Find someone that has an ac ammeter and measure the load. Do not install a bigger breaker unless your wire and equipment are sized for it.

A good electrician will save you money and possibly grief.
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Old 03-10-2013, 16:05   #10
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I have had the same problem in the past. Before replacing anything, install or have installed a Blue Sea Digital Volt-Ammeter. I don't work for them, but I do have one. It can tell you, second by second' what your AC system is doing.

You can't troubleshoot a problem until you have a way of seeing. What it is doing. Well, you can - you can keep throwing money and parts at it until you fix it or run out of money!
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Old 03-10-2013, 17:13   #11
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Re: Why does my main AC breaker keep tripping?

I recently solved the identical problem with the AC 30 amp and several smaller AC circuit breakers. They were all original to the boat which was built in spring 1994.

The breakers had intermittently high internal resistance. I detected this by disconnecting each breaker and removing it from the panel.

I then connected my Fluke DVM in resistance mode (measuring ohms) in series thru the circuit breaker. When the breaker was open there was infinite resistance - an open circuit - just as there should be.

BUT - when I closed the circuit breaker I would see almost zero resistance ( less than 1 ohm) most of the time. Wiggling the circuit breaker lever or tapping the breaker would sometimes cause the resistance to jump up to many hundreds of ohms. Wiggling or tapping some more would make the resistance drop back to almost zero.

When the resistance is high - the breaker heats up and trips out if a high amp load such as water heater, battery charger, or microwave is running.

I replaced the circuit breakers and have had no recurrence of the intermittent circuit breaker opening - even while pulling 25 amps at 120V.

This has also happened to four of my DC breakers.

They are all Ancor breakers and in a clean dry location.
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Old 03-10-2013, 17:26   #12
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Re: Why does my main AC breaker keep tripping?

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.
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Old 04-10-2013, 02:36   #13
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Re: Why does my main AC breaker keep tripping?

with all that stuff you are likely just running too much. probably not a bad breaker. time to upgrade the boat to dual 30a or a 50a. and find a slip with that too... or cut back on the power.
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Old 04-10-2013, 09:26   #14
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Re: Why does my main AC breaker keep tripping?

Quote:
Originally Posted by Toubab View Post
I've got a 30 amp breaker for my main AC supply that runs my air conditioning, a few AC outlets, battery charger, and refrigeration. It will randomly trip pretty often. It does happen more often when I'm running more stuff but it also happens a lot when I'm just sleeping with the air conditioning on. I added the AC refrigeration since buying the boat but this was happening before that. I'm also planning on adding a second battery charger so I'm worried that I'm overloading the breaker.

So can/should I just put in a larger breaker? I don't think there's an actual short anywhere since sometimes I can go for days without it tripping.

Oh and I'm at a dock with shore power. I think it's only a 30 amp supply if that matters.

Thanks!
Most AC units draw about double their rated power draw on startup; it's only for a few seconds, so doesn't usually matter. What size is your AC?
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Old 04-10-2013, 09:40   #15
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Re: Why does my main AC breaker keep tripping?

Why all this mindless speculation?

Put a clamp-on Digital recording amp meter on the black wire leading from the shore receptacle to the circuit breaker.

MEASURE the various loads individually - including inrush / startup current for the various compressors / motors. WRITE down the results

Then measure the combined loads in various combinations. WRITE down the results.

You will then see IF the combined loads are too much for the breaker and if so - which loads you will have to ensure do not occur simultaneously

this is not rocket science - it is a measurement problem - if you don't measure then all you are doing is guessing!

I've done this process many times - it is not complicated - just a little tedious
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