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Old 06-14-2019, 03:57 PM   #1
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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.
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Old 06-14-2019, 04:04 PM   #2
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Good reminder. However, Iíd 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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Old 06-14-2019, 05:06 PM   #3
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Grab the ends of those cables every day if you can. If you feel warmth, investigate.
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Old 06-14-2019, 06:04 PM   #4
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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.
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Old 06-14-2019, 07:19 PM   #5
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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 canít 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.
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Old 06-14-2019, 07:26 PM   #6
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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.
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Old 06-14-2019, 10:05 PM   #7
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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.
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Old 06-14-2019, 11:24 PM   #8
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Aviation rule: Reset a breaker once; NO MORE. Fail the system and down the aircraft on arrival.
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Old 06-15-2019, 10:05 AM   #9
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Quote:
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Aviation rule: Reset a breaker once; NO MORE. Fail the system and down the aircraft on arrival.

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!
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Old 06-15-2019, 10:12 AM   #10
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Good reminder. However, Iíd 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?
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.
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Old 06-15-2019, 10:14 AM   #11
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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.
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Old 06-15-2019, 10:29 AM   #12
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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.
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Old 06-15-2019, 12:07 PM   #13
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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.
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Old 06-15-2019, 12:31 PM   #14
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As others have noted, if I had a 30amp inlet, Iíd 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 donít worry about it.
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Old 06-15-2019, 01:38 PM   #15
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Quote:
Originally Posted by dhays View Post
As others have noted, if I had a 30amp inlet, Iíd 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 donít worry about it.
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.
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Old 06-15-2019, 05:55 PM   #16
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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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Old 06-15-2019, 06:09 PM   #17
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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
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Old 06-15-2019, 06:14 PM   #18
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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.
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Old 06-15-2019, 07:08 PM   #19
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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.
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Old 06-15-2019, 07:15 PM   #20
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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 Iím 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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