AC Breaker tripping but not on Generator power

[Squanderbucks]

Hi
Years ago I added a second 30AMP elecrical line and breakers system to my 38 ft powerboat. One 16K Dometic AC runs off Shore power 1 and a second runs off Shore Power 2 set of wiring.Each 30AMP has it's own breaker paned and main circuit breakers.
However, now when the 16K AC on Shore 1 is turned on it trips the onboard breaker dedicated to the AC and the Breaker in the Dock's power pedistal.
No other breakers are tripped - not Main Breaker for the Shore 1.

When the Dock Pedistal trips of course my Shore 2 power is lot also because I am using a single 50AMP shore power cord with a Marinco splitter at the boat's two 30 AMP recepticles.

If I switch to running off the Generator an 8KW model the 16K AC runs just fine and no breakers trip. So I don't think the problem is in the breakers on the boat or the AC itself. Am I correct to start looking at some weak connection somewhere in the wiring between the Shore Power Plug Inlets on the boat and the Main Breaker. Or possibly the Rotary power Selector switch wiring on the bulkhead where power is switched fron Dock-OFF-Generator?

Any suggestions to help narrow my search before tearing things apart would be appreciated.

What I have tried is a different power cord from the Dock to the boat Shore 1 inlet and a different 50 AMP recepticle on the dock power stand. No differences.

[SailingHarmonie]

Are any of these breakers tripped by ground faults? Or are they over-current protection only?

[Squanderbucks]

This boat was built in 1965 there are no GFI outlets in the boat wiring. I do have dual digital AMP meters for each line. There does not seem to be any excess draw when running the AC while on generator power. The unit has a soft start accessory installed and startup AMPs on the generator where I csn read the numbers don't show a high draw - around 12-13 AMPS then drops while running I think to around 8-9.

When running off shore power it immediately trips so I never get a current reading. Also. if running on the generator and then plug into shore power and switch over to Shore Power on thew Rotary Dock-Off-Generator switch it immediately trips both the boats AC breaker and the Shore Power pedistal.

No other breakers trip - On Board Main. I just remembered that I built in a second Rotary switch right at the AC to allow running the AC off the Shore Power 2 line. I may try switching it over to Shore 2 temporarily and see if it shuts down the same way. Then I may narrow down the areas to look for a short or bad connection, I've never had to use this second rotary switch in the 15 years the rewiring was done.

[SailingHarmonie]

Originally Posted by Squanderbucks

This boat was built in 1965 there are no GFI outlets in the boat wiring.

Sorry, but I need to be sure you understand the question, since you did not answer the question I asked: Are any of these BREAKERS fault sensing? Including the one on the shore power plyon?

That is completely different than having GFI outlets.

Sorry to be pedantic on this, but your symptoms sure sound like a ground fault and NOT a overload. Or maybe a shore power wiring mistake. Are hot neutral and ground where they are supposed to be?

[GreenWave]

So you are splitting a 50amp service at the dock into two 30 amps with two plugs entering your boat?


Check these things:
1) Try a totally different plug adapter and cord for the service that is tripping
2) Inspect the cords for corrosion and clean up
3) Inspect the receptacle on your boat for corrosion an clean. Look at the back side where the wires connect. If you see any signs of corrosion or arcing, replace.


If you can get a different 50amp/30 amp adapter and cord and try that I would.


If all else fails then might look into the shore power pedestal itself.

[Gudgeon]

It does sond like it could be a ground fault is the pier 50 amp power a 125 Volt 50 amp o5 250 volt 50 amp?

[Squanderbucks]

Thanks guys for your input. Some of your qustions I a a little vague on as I am not really an electrician. I can follow a wiring diagram and run wires, install stuff but having a real understanding of the workings of electrical systems is not my strong point.

The marina shore power pedistal has a breaker with a 10AMP Ground Fault Indicator - at least that is what I beleive it to be. The breaker switch has below it a red indicator when the breaker gets tripped. Not just the switch moving to off position.

I have been at this marina about 2 months without an issue until a week ago. First symptoms were when switching from Genset to Shorepower using the Rotary switch the Dock breaker would trip. But AC lran normally. Then one day the power was on from the dock and everything was perating normally for several hours with the AC on. Then the Breaker on the Dock and the individual breaker for just the AC in the boat panel both tripped.

I am hauling the boat Tuesday for bottom painting and to replace the thru hull for the head. While it's out I will trace down all the connections and possibly hookup water to the AC and see what happens when plugged into the yards power. After that the boat goes back to my home dock.

I did try a second 30AMP power cord to asecond Input recepticle on the boat with no difference. The boat is setup with two sets of power inlets - one pair on the Starboard side ( standard Marinco plugs) and a second pair on the Port side with Smartplugs.

[Turtle Blues]

You run without issue on genset. This would indicate the fault is in the dock power supply.
If the breaker trips immediately on energizing this would indicate a fault rather than overload.
if you have inspected all cord connections and find no discoloration or indication of shorting ask the Marina to inspect the pedestal and associated wiring. I have seen instances of bug infestation inside the pedestal shorting connections, wiring frayed due to constant dock movement,etc. and breakers are capable of going bad.

[Squanderbucks]

Ok took the boat back home to my own dock which ahas a commercial pedistal purchesed and setup probably back in 2004. It has two 30 amp cord recepticals for boat cords. One has a 30 AMP breaker and the other a 20 AMP. When to boat is plugged in at the home dock there is no breaker tripping.

I think the problem is with the Marina breaker. I was able to run on the marinal power for two months with no problem then the breaker issue began after one day when I was on the boat doing some routine tidying up the power shut down. That is when I discovered the problem. Nothing had beed changed electrically up to that point. I think their breaker just went bad.
I tried two different cord sets while at the marina as part of my checking things out. All with tthe same result.

Thnaks all