Scary Breaker Trips

Well, we started living aboard on December 17th the day we knocked the house down, (she was flooded by Irma). We bought the boat and spent four months refitting her for live aboard, mostly fixing a number of electrical issues to do with a blown inverter, fixing the typical marine trader window leaks and installing a Type I MSD so pumping is not necessary.

The first month went well, but the second month we had problems with the 50 amp breaker on the temp pole for the dock. It went from once every two weeks tripping, to daily so we got a replacement. No more pole tripping.


However, a week or so goes by and now one of the thirty amp breakers on the panel tripped about once every three weeks or so, then every two, then once a day, the more. We started better power management and it was better, but it still tripped on occasion. I called my Marine Electrician. He came out, looked at the breaker and pronounced it OLD and ordered a new one.

The new one broke on entry, bad plastic mold, but his assistant kept complaining about how hot the old one was. So, the electrician checked the cables and boom.

So, $500 new shore cables, new inlet, new breaker and we are OK. Never smelled it once! Moral, do not ignore the breaker, it is trying to tell you something. No internal wires were melted, only the inlet and the shore power cable.

Good reminder. However, I’d like of like to know why the inlet got so hot it melted? What was the condition of the end of the cable? What was the condition of the inlet? Was a dielectric grease used to protect the connections?

Grab the ends of those cables every day if you can. If you feel warmth, investigate.

The shore power cord ended up in the water at one point. Takes years for the salt to corrode the female socket but eventually you get a catastrophic failure.

The 5L-30 plugs do not have a very large contact area to conduct up to 30 amps. They probably should be only run at 70% of the 30 amps or so. A little bit of corrosion on the contacts will quickly become a problem. I went to Smart plugs for this reason. CMS web site has a very good review of this situation. I can’t believe that it took a marine electrician several tries to find this problem, it would be the first thing I would look at if the breaker is repeatedly tripping. It is a very common problem.

Corrosion on contacts equals resistance. Resistance on contacts means voltage drop and more current being drawn by onboard devices. Higher current through a resistance equals heat. Lots of heat equals melted plug. Guess which terminal had the corrosion?

Keep those shore power contacts CLEAN (both sides). Dielectric grease does help keep corrosion at bay.

I use dielectric grease on mine, but it is time to remove the dock pedestal end and clean, inspect, and apply new dielectric grease. I have been doing this a couple times a year but it has been longer than 6 months since I last did it. This thread is a good reminder for me.

Aviation rule: Reset a breaker once; NO MORE. Fail the system and down the aircraft on arrival.

AlaskaProf said:

Aviation rule: Reset a breaker once; NO MORE. Fail the system and down the aircraft on arrival.

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That should have been a rule for my boating too. My problem, or stupidity, was that I just thought the breaker was old and getting "touchy" as we were running both the window shaker and the main AC on that leg pulling about 15 amps. So much for thinking.


Funny thing is, I am a programmer, I should know better!

dhays said:

Good reminder. However, I’d like of like to know why the inlet got so hot it melted? What was the condition of the end of the cable? What was the condition of the inlet? Was a dielectric grease used to protect the connections?

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Dave, this shows the value of a good marine surveyor, as I had a terrible marine surveyor recommended by the boat broker. I pointed out the small defect in the cable and he said, "Oh, that is from when the battery charger/inverter blew. That chord is fine!"

I have always had boats 20' or less, no shore power, just 12 volt systems and chargers. This is my first big one. I am learning a lot, but no one mentioned "Dielectric grease" to me. I am on my way to WM to get some now, thanks.


As to the condition of the cable, it looked good other than that small melt around one connector which surveyor said was fine. Inlet looked good too, but I bet if I would have looked harder I would have seen some rust. Just glad we did not have a fire. I feel these puppies each day now when I exit the boat.

Yep I've had several friends/associates that have had issues with the old 30AMP plugs/inlets. When we were looking at boats always assumed I would switch to Smart Plug if we bought a 30A boat. But ours is a 50Amp/125 boat and the old 50A plugs are much more robust and we have had no problems (Did put a new shore -end plug on one of the 3 25ft lines). With both 16k AC's, water heater and microwave running (and all lights are LED) we draw around 36amps.

The nickel plated pins on the smart plug receptacle are corrosion free and look just like the day I installed it.

Everyone frets about untinned wire on a boat, when the ABYC NEMA plug is probably the most corroded, and therefore high resistance, component that is in the electrical system.

Breaker rarely go bad, not impossible but certainly not frequently so that would not be at the top of my troubleshooting list. However the shore power cables are notofor melting due to resistance.

As others have noted, if I had a 30amp inlet, I’d replace it with a Smart Plug. I did this on my last boat. Now with a 50/120 inlet, my only problem is that it is getting to be rare. It is a very solid connection and I don’t worry about it.

dhays said:

As others have noted, if I had a 30amp inlet, I’d replace it with a Smart Plug. I did this on my last boat. Now with a 50/120 inlet, my only problem is that it is getting to be rare. It is a very solid connection and I don’t worry about it.

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Yep, hard to find 50A 120 pedestals. First thing I bought was an expensive adapter for 50A 120 to 50A 240. The boat had one for 50A 120 to 30A.

Check your loads. There is nothing wrong with the “normal” 30 amp plug as long as its clean and not overloaded.

30 amps is 3600 watts: one battery charger, one hot water tank and a few lights. That’s it. 90% of maximum load is 3250 watts. More than that and the available voltage drops and you get these wiring issues.

Monitor your loads! 50 amps is 6000 watts, that’s one hot water tank, one battery charger, fridge, lights, maybe an air conditioner but not a microwave and a toaster. 90% is 5400 watts. That’s 3 normal kitchen appliances and a few lights and NOTHING ELSE.

Shore power will never give you as much power as your house, did I say don’t overload!?

I’ve been yapping about this forever and nobody seems to pay the slightest notice. Check the voltage at any outlet and if it is less than you expect, ie less than 120, you are overloaded and a Smart plug won’t make a particle of difference.

How do people monitor there loading? Do you run a amp measuring clamp and just turn items on and off to get the draw? Or is there a table of common loads? Like on marine ac unit is xxxx Watts? Is there something I could hard wire into my 120v system that is like a Killwatt meter for the boat? My main panel only has voltage meter FYI.

I have a shunt on my house bank connected to monitoring system. Measures amps in and out real time. Very useful

My main electrical panel has meters for voltage and current for both 12 volt and 120 volt. I do have to select which 30 amp inlet the meters are monitoring with a small switch.

I have 2 Blue Seas 8247 digital panel meters that are multifunction.

I mounted one coil at the inlet before the inverter/charger and another coil after the inverter.

An amp meter measuring only at the panel will give an erroneous reading depending on if the inverters transfer function is utilized.

With the inverter wired directly to the shore power for transfer function, reading amps at the panel does not measure the battery charger load.

Victron Multiplus has a feature to automatically turn off the hot water tank when on inverter. That doesn't get measured at the panel either.

Like others, I have a Blue Seas digital panel that gives info on my AC loads. I do keep an eye on it to make sure that I’m not pushing my loads too high. It means that I have to be selective as to what AC loads are running.

dhays said:

Like others, I have a Blue Seas digital panel that gives info on my AC loads. I do keep an eye on it to make sure that I’m not pushing my loads too high. It means that I have to be selective as to what AC loads are running.

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Where is the coil mounted?

syjos said:

Where is the coil mounted?

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To be honest, I’m not sure. It has been installed since new. I believe it is between the main breaker and the AC distribution panel. All are located at one panel.

"How do people monitor there loading?"

Weather the loads are winter electric heat or summer air cond the simple way to monitor the loads is to tale a look at the plug and sockets that bring power on board.

The black burned look is easy to notice.

Xsbank said:

Check your loads. There is nothing wrong with the “normal” 30 amp plug as long as its clean and not overloaded.

30 amps is 3600 watts: one battery charger, one hot water tank and a few lights. That’s it. 90% of maximum load is 3250 watts. More than that and the available voltage drops and you get these wiring issues.

Monitor your loads! 50 amps is 6000 watts, that’s one hot water tank, one battery charger, fridge, lights, maybe an air conditioner but not a microwave and a toaster. 90% is 5400 watts. That’s 3 normal kitchen appliances and a few lights and NOTHING ELSE.

Shore power will never give you as much power as your house, did I say don’t overload!?

I’ve been yapping about this forever and nobody seems to pay the slightest notice. Check the voltage at any outlet and if it is less than you expect, ie less than 120, you are overloaded and a Smart plug won’t make a particle of difference.

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So, here is my question and please forgive my ignorance. On a 50-amp boat, are not two legs coming from the pedestal hot and do not each of these legs deliver 50 amps to the panel for a total of 100 amps? As is typical, my boat has a separate panel that is only fed by shore power or generator. Isn't this where one of the hot legs goes? Doesn't the other hot leg feed the rest of the AC loads via the "main" panel thus a total of 100 amps of availability? Doesn't my 14.5 Kw generator supply about 100 amps of AC to mimic shore power? I gots to know.

dhays said:

To be honest, I’m not sure. It has been installed since new. I believe it is between the main breaker and the AC distribution panel. All are located at one panel.

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You should look for the coil one day when you have nothing to do to see what it is measuring.

Where that coil is located will make a difference in the AC amp reading equal to the charger consumption if the inverters transfer function is used.

A client kept popping 30 amp main breakers frequently. He was watching the AC meter monitoring the panel and the main breaker would break when he was running 25 amps or less. His generator would pop it's 45 amp breakers when running 40 amps or less.

His panel amp meter was measuring current at the panel input. It was not measuring the current used by the charger part of the inverter.

We put in a second coil before the inverter/charger and the meter measuted 5 to 12 amps higher due to the battery charger. The amperage difference depend on the batteries state of charge. We installed a two pole switch so he could switch between coils for when he was on inverter or shore/generator. He eventually installed a second meter for simplicity.

Volt meter on any leg of the 120 system will tell you. As soon as the voltage drops below the amount you measured at the pedestal, you are overloaded.

syjos said:

His panel amp meter was measuring current at the panel input. It was not measuring the current used by the charger part of the inverter.

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Ah I see now. Yeah, I can see where that would be a big problem. I will dig around and see.

However, if I turn the charger on, I do see an increase in the amp draw on the meter. Based on that, I think the coil is just after the input selector switch as the behavior is the same whether it is on the forward or after AC inlet, or the genset.

dhays said:

Ah I see now. Yeah, I can see where that would be a big problem. I will dig around and see.

However, if I turn the charger on, I do see an increase in the amp draw on the meter. Based on that, I think the coil is just after the input selector switch as the behavior is the same whether it is on the forward or after AC inlet, or the genset.

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Is your charger an inverter/charger or dedicated charger?

Does your inverter/charger do the switching or do you use the selector switch mentioned above to select an AC source? If you switch between inverter - generator - shore with the selector switch, then your meters coil is correctly positioned.

The amp meter erroneous reading issues is only relevant when the inverter is wired to do the switching between shore and inverter automatically.

syjos said:

Is your charger an inverter/charger or dedicated charger?

Does your inverter/charger do the switching or do you use the selector switch mentioned above to select an AC source? If you switch between inverter - generator - shore with the selector switch, then your meters coil is correctly positioned.

The amp meter erroneous reading issues is only relevant when the inverter is wired to do the switching between shore and inverter automatically.

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It is an inverter/charger. You raise a question that I’ve never thought about....

The selector switch only selects between the two power inlets (bow or stern) and the genset.

If the inverter is not disabled, then it will start inverting as soon as the AC power is stopped. So for example, if I turn the shore pedestal off, the boat will start inverting automatically IF the inverter is left on. After one bad experience, I turn the inverter off unless I want it inverting.

As I think about it now, I don’t think my AC meter is on at all when there is no external AC source. If the inverter is inverting, the AC meter stays dead. My inverter/charger display shows the number of amps that is being provided from the DC-AC conversion.

I was on the boat today and had the inverter on. The AC meter was dead. When we got back at the dock, I plugged the boat in, and the AC meter didn’t come alive until I switched the AC input to the live AC inlet.

So, this would indicate to me that the coil is between the AC source selector and the AC panel. However, the inverter output goes to the AC panel without going through the coil. Does that make sense?

That's a typical installation using the inverters transfer function.

If the meter is not reading when on inverter, then you need a second coil or meter. Unless the inverters panel has an amp meter.

I have a second Blue Seas meter with coil mounted after the inverter

When on shower power and generator, I tell my wife to monitor the meter with the highest reading since both meters are active. The meter with the lower reading is monitoring the inverter pass through current and the higher reading meter is reading actual generator or shore current.

On inverter, only one meter will be active, which is reading inverter output.

These Blue Seas meters have large bright red numbers that can be read from across the boat making monitoring easy.