Main breaker

[Overvolted]

Measure voltage between the Hot and Ground and the Neutral and Ground.
If there is leakage the 120 volt nominal voltage (differential) between Hot and Ground will be less than 120 volts and show a corresponding increase in voltage between the neutral and ground.
Start the testing will all the boats devices turned off and get a baseline. Then start turning things back on taking measurements at each step. The more load the more current on the neutral. There should always be a differential of 120 volts between the hot and ground in a healthy electrical system. With everything off there should be a very voltage between the neutral and ground.
As an FYI the typical culprits that leak to ground are AC compressors, Refrigeration compressors, and water heaters. The battery charger could also.

Assuming your boat doesn't have an inverter and generator is switched out of the system the neutral and ground conductors are tied together at the marina's main power panel at the utility source. The length and resistance of those conductors will support the differential testing at your boat. Other boats on the same circuit can mask results and the reason for the baseline test.

So we have been at the marina all day and just now and the main tripped. I measured 126 on the hot side and 30 on the neutral. I had all breakers off. Then the fridge cycled on from the 12 volt side so I shut it off and remeasured. The neutral side went down to 20 volts and hot side stayed at 126 volts.

 

[Overvolted]

Yesterday when the main tripped i measured 30 volts on the neutral at the shore power switch in the boat and the breaker would not reset. All breakers were off when I saw 30 volts. The refrigerator is 120/12 volt and when I turned it off from the 12 volt side I remeasured the neutral and had 20 volts.

I then turned the main back on and it stayed latched with 20 volts on neutral side. One by one we turned the breakers on and their corresponding appliance and the neutral never changed from 20 volts. Once we had ALL appliances running including microwave and A/C voltage on neutral only dropped by a few 10ths to about 20.2 volts.

Its been about 16 hours since I saw 20 volts on neutral and everything has been running as it should.

Today I measured neutral at my power cord from the marinas pedestal and saw 4.6 volts. I plugged it back into the boat and measured 5.6 volts on the neutral at the shore power selector switch. With the meter connected we turned on our electric cook top and still had 5.6 volts on neutral.
What could have caused the 30 volts i was seeing on neutral and now all I see is 5.6? Intermittent electrical problems suck.

 

[hughespat57]

Yesterday when the main tripped i measured 30 volts on the neutral at the shore power switch in the boat and the breaker would not reset. All breakers were off when I saw 30 volts. The refrigerator is 120/12 volt and when I turned it off from the 12 volt side I remeasured the neutral and had 20 volts.

I then turned the main back on and it stayed latched with 20 volts on neutral side. One by one we turned the breakers on and their corresponding appliance and the neutral never changed from 20 volts. Once we had ALL appliances running including microwave and A/C voltage on neutral only dropped by a few 10ths to about 20.2 volts.

Its been about 16 hours since I saw 20 volts on neutral and everything has been running as it should.

Today I measured neutral at my power cord from the marinas pedestal and saw 4.6 volts. I plugged it back into the boat and measured 5.6 volts on the neutral at the shore power selector switch. With the meter connected we turned on our electric cook top and still had 5.6 volts on neutral.
What could have caused the 30 volts i was seeing on neutral and now all I see is 5.6? Intermittent electrical problems suck.

Sorry for slow response
Yes tracking down this issues can be tedious and frustrating.

So first
Unplugging and testing at the cord was a good start.
Right there it should have been
H N 125
H G 125
N G 0
I think the issue could be on the dock.
Try again at the pedestal itself.
If you don’t get 125 H G the ground may be bad.

Th only place G and N are supposed to be connected is at the main panel of the marina.
There should be no voltage possible between N and G if that is correct.

 

[ttmott]

Voltage on the neutral can be dependent upon other boats on the same circuit near your boat. You are measuring the neutral against the ground right?
Is the hot to ground steady at nominal 120 volts?
The idea of the test is to determine current on the ground conductor at any appreciable value (like the trip point of that circuit breaker). If the neutral to ground nominally changes and the hot differential to ground reduces then you can assume there is current on the ground which there should be none.

Another thing you can do is disconnect the ground from that circuit breaker's sense module and see if trips continue. But, what it appears from what you see so far (still early in testing) is the circuit breaker is failing as @hughespat57 alludes. We just haven't gone through all of the "suspects".

 

[Overvolted]

Sorry for slow response
Yes tracking down this issues can be tedious and frustrating.

So first
Unplugging and testing at the cord was a good start.
Right there it should have been
H N 125
H G 125
N G 0
I think the issue could be on the dock.
Try again at the pedestal itself.
If you don’t get 125 H G the ground may be bad.

Th only place G and N are supposed to be connected is at the main panel of the marina.
There should be no voltage possible between N and G if that is correct.

At the pedestal
H G 121
H N 121
N G 4.5

 

[Overvolted]

Voltage on the neutral can be dependent upon other boats on the same circuit near your boat. You are measuring the neutral against the ground right?
Is the hot to ground steady at nominal 120 volts?
The idea of the test is to determine current on the ground conductor at any appreciable value (like the trip point of that circuit breaker). If the neutral to ground nominally changes and the hot differential to ground reduces then you can assume there is current on the ground which there should be none.

Another thing you can do is disconnect the ground from that circuit breaker's sense module and see if trips continue. But, what it appears from what you see so far (still early in testing) is the circuit breaker is failing as @hughespat57 alludes. We just haven't gone through all of the "suspects".

Hot to ground is steady at 121 V.
Neutral to ground is steady at 4.5 V.

 

[Overvolted]

When the main first tripped and would not reset I switched generator on and reset the main. It stayed latched and everything worked correctly. As soon as I shut generator off and switched to shore power the main tripped.This is when i was seeing 30 V on the neutral. If I run off the generator, Onan Ensign 4.500 there are no problems.

Appreciate all the help with this.

 

[hughespat57]

When the main first tripped and would not reset I switched generator on and reset the main. It stayed latched and everything worked correctly. As soon as I shut generator off and switched to shore power the main tripped.This is when i was seeing 30 V on the neutral. If I run off the generator, Onan Ensign 4.500 there are no problems.

Appreciate all the help with this.

I think there os a ground problem on the dock.
Few boats have your feature none that are newer.
Lift one wire off the SP coil and tape it up.
Tell th marina they have a ground problem

 

[ttmott]

When a generator is transferred the ground and neutral are combined and both disconnected from the shore power. Like the Utility source the generator is classified as a power source and must tie the neutral and ground. Same for an inverter.
So that seems to isolate the shore power feed into the boat and to the transfer switch. There could be a nearby boat polluting the ground also. That would be a dangerous situation.
There have been instances reported on this forum on shorts due to corrosion behind the shore power cord interface on the boat.

As an afterthought - your boat should have galvanic isolators which could be toast if this situation unfolds to be a marina problem.

 

[Overvolted]

Just a quick update, the marina says it is a problem on my boat and not at their pedestal.
This issue first showed up after one of the docks came loose in a storm and broke a wire that left my dock out of power. Marina said then it was an issue on my boat.

So now everything is new from the pedestal to my main breaker and im back to square one with tripping the main. I'm pretty sure its a combo of their crap wiring and some derelict boats on my dock.

Thank you guys for all your help.