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Old 19-02-2018, 08:24   #1
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Main breaker popping at 10A

Good day all,

Over the past few months, I've noticed that the 30A main shore power (125V) breaker on my Nauticat 40 will pop when I am running about 10A worth of appliances. For example, if I run one space heater at 1500W it will pop, but if I run 500W and 650W heaters it will make it through the night.

I initially suspected a faulty breaker, but I noted that it gets warm to the touch when it pops. This makes me think that, as a thermal breaker should, it is behaving itself. Of note, my voltmeter that is built into the system shows 125V.

I'm reasonably familiar with 125V systems as I installed the 125V systems on my previous 2 boats. But I guess since they were newly installed systems (by me) I never had to troubleshoot any problems such as I'm having now.

Any ideas or suggestions on how I can pin down this issue would be appreciated.

Thanks!
Korvessa
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Old 19-02-2018, 08:52   #2
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Re: Main breaker popping at 10A

Either bad wiring at breaker (lose connections getting hot) Or bad breaker. Look at the back.

Measure actual current to confirm draw.
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Old 19-02-2018, 09:15   #3
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Re: Main breaker popping at 10A

If the breaker is getting warm , replace it. Breakers fail with age and corrosion. If you want a cheap way to confirm that it's the breaker, back feed your panel through one of the other breakers preferably a 20 amp one. But as cheap as they are, just replace it.
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Old 19-02-2018, 09:16   #4
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Re: Main breaker popping at 10A

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Originally Posted by smac999 View Post

Measure actual current to confirm draw.
Thanks for the suggestions. Your suggestion of measuring actual current makes me realize that my voltmeter isn't up to the job. Lucky for me I like buying tools...

Do you have a suggestion for a good meter that measures amps?

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Old 19-02-2018, 09:37   #5
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Re: Main breaker popping at 10A

If you have an ammeter up-stream from the breaker just watch that while you cycle the breaker.

But I agree with the others. I've had four breakers die on my boat over the years. Each time it worked OK but popped at a lower amperage than it used to. It's easier to diagnose the problem by first replacing the breaker. If that doesn't fix it, then get out the multimeter.
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Old 19-02-2018, 09:48   #6
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Re: Main breaker popping at 10A

The Fluke
Clamp On Ammeters are great. I have a model 337
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Old 19-02-2018, 09:55   #7
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Re: Main breaker popping at 10A

Running heaters, even within spec, often fries things gradually. When I lived aboard in the PNW, I had to replace the 30 amp shore power cord every year due to the receptacle just burning up slowly. I didnt have a 1500 watt heater, but more like 1100/1200 max. Often run on the lower setting. The inside of your breaker may be pretty brown too!
... and yes to breakers failing now and then even on the 12V side...
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Old 19-02-2018, 23:35   #8
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Re: Main breaker popping at 10A

Quote:
Originally Posted by Korvessa View Post
Thanks for the suggestions. Your suggestion of measuring actual current makes me realize that my voltmeter isn't up to the job. Lucky for me I like buying tools...

Do you have a suggestion for a good meter that measures amps?

Korvessa
get a clamp meter that can measure both AC and DC current.

Fluke is really good. cheaper stuff likely work just fine too.
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Old 20-02-2018, 00:17   #9
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Re: Main breaker popping at 10A

Breakers trip when an internal metal piece distorts because too much amperage is passing thru. Over time the distorting metal becomes fatigued and trips at a reduced amperage.
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Old 20-02-2018, 08:09   #10
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Re: Main breaker popping at 10A

I had an electrician explain that a circuit breaker should be replaced if it ever trips to protect a circuit - it's a "controlled explosion" and is really meant for only a single use? Turning it on and off as a switch is also not desirable for a typical breaker. Maybe another electrician can clarify this for us all?
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Old 20-02-2018, 08:15   #11
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Re: Main breaker popping at 10A

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Originally Posted by RobinScurr View Post
I had an electrician explain that a circuit breaker should be replaced if it ever trips to protect a circuit - it's a "controlled explosion" and is really meant for only a single use? Turning it on and off as a switch is also not desirable for a typical breaker. Maybe another electrician can clarify this for us all?
I'm suspicious of that advice. If a breaker is a single use item, then it is inferior in every way to a fuse.

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Old 20-02-2018, 08:27   #12
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Re: Main breaker popping at 10A

Quote:
Originally Posted by pesarsten View Post
If the breaker is getting warm , replace it. Breakers fail with age and corrosion. If you want a cheap way to confirm that it's the breaker, back feed your panel through one of the other breakers preferably a 20 amp one. But as cheap as they are, just replace it.
Not sure if you are plugging into the same outlet each time.
Corrosion internally at the outlet, will cause resistance, or in the breaker it self.
At the screw attachments on the plug outlet.
A lot of outlets are push in the bare end wires for connections, not correct.
AC wiring needs a solid connection in marine application, hook connectors or ring to the screw ends.
Solid crimps on the wires, heat shrink to the connector ends. Older vessels, and most mass produced, boat manufacturers do not spend the time to do this step.
There are plug in amperage draw measuring devices available a Home Depot, Lowes, electrical stores.
Check each plug, for excessive amp draw.
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Old 20-02-2018, 08:51   #13
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Re: Main breaker popping at 10A

Quote:
Originally Posted by Korvessa View Post
Good day all,

Over the past few months, I've noticed that the 30A main shore power (125V) breaker on my Nauticat 40 will pop when I am running about 10A worth of appliances. For example, if I run one space heater at 1500W it will pop, but if I run 500W and 650W heaters it will make it through the night.

I initially suspected a faulty breaker, but I noted that it gets warm to the touch when it pops. This makes me think that, as a thermal breaker should, it is behaving itself. Of note, my voltmeter that is built into the system shows 125V.

I'm reasonably familiar with 125V systems as I installed the 125V systems on my previous 2 boats. But I guess since they were newly installed systems (by me) I never had to troubleshoot any problems such as I'm having now.

Any ideas or suggestions on how I can pin down this issue would be appreciated.

Thanks!
Korvessa
I had a similar issue. I found a corroded splice in the main triplex wiring from shore power plug to a/c breaker panel. Not sure why they spliced but it was done terribly with crappy butt connectors and electrical tape. Check all connections for corrosion and loose screws, anything that will induce resistance. When diagnosing electrics I start with in this order, Source-Path-Load. Good luck!
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Old 20-02-2018, 09:20   #14
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Re: Main breaker popping at 10A

I doubt you meter isn't up to the task. Replace the breaker. If you had a bad connection to make a 30A break trip at around 10A you would have already burnt to the waterline.
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Old 20-02-2018, 09:42   #15
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Re: Main breaker popping at 10A

I agree with previous posters that the likely problem is a bad breaker. They don't last forever.

As to potential bad connections, an easy test is to load your system whilst monitoring the voltage. Monitoring the voltage at the panel will tell you if you have a bad connection between the pedestal and the panel, say at the shore power inlet. Measuring at the load will tell you if you have a bad connection between the panel and the load.

Don't be surprised or worried if you have some voltage drop, say 5 or even 10 volts, but if you voltage is dropping into the double digits, you've got a problem. If you're seeing anything less than 100 volts, look for something hot.
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