AC Lights Tripping GFI at shore Power outlet

[tec10]

Damned if I can get this one. I sincerely hope someone out there can help.
Attached to GFI outlet at dockside(15 amp) via 15AMP pigtail converter, into my 30A cord. Good connections, good power to panel. All other circuits are fine. I have used this hoockup and never had a problem before.
When I flip the "AC Lights" in the cabin, it immediately trips the GFI at dockside. When I use the "DC Light Switch",I am fine.
My original thought was this circuit must have a bad ground on the panel, but wanted to see if anyone thought I was on the right track. Could be a bad breaker too??
Please help electricians.

2002 260 Sundancer
5.0MPI BIII

 

[rondds]

Do you have a microwave on the boat? If that runs without tripping the GFCI (huge power consumption), you've probably got a bad breaker or a short in your AC lights circuit somewhere. In any event, sounds like a beech to find.

 

[Kay Lee]

Is the "AC Lights" breaker the only breaker that causes the GFCI to trip? If so, you've got a short or the beginnings of a short in your AC light wiring. If not, meaning that if any breaker will cause the GFCI to trip, borrow someone's 15-to-30 amp adapter for a test.

Larry

 

[Four Suns]

These things are not that hard to find if you know what you are looking for. A GFI plug and a circuit breaker perform two very different functions and a short (like connecting the hot and neutral together) will not necessarily pop a GFI unit. You can blow a breaker and the GFI can still be engaged. A breaker pops when enough heat is generated inside the breaker from an overload condition. A GFI plug/unit does not look at overload conditions but monitors the current coming in on the hot wire (black) and the current leaving on the neutral wire (white). If the electrons coming in and going out don't match, the GFI will pop. This can happen on a boat from improper wiring or installing a household appliance on a boat that bridges the grounded neutral (white) with the ground (green). You can do that in your house (you shouldn't but manufacturers do... like on that 2003 vintage clothes dryer I have) but not on your boat. The GFI basically looks for electrons/current finding ground other than where you want them to (i.e. the white neutral wire) and this can happen without ever producing an overload situation that will pop a breaker. How this is designed in a land-based house versus a boat is different....

Look at this diagram:

The one thing you need to look for on that lighting circuit is if any of the switches or connections behind the panel have connected the white neutral line to the green ground line.... or if a green ground line has come lose and is touching a white neutral line... Or if you have plugged ANYTHING into a plug on that circuit (like a small appliance, hair dryer, toaster, etc) that is bridging green ground to white neutral.

In your house, the white neutral and green ground are bridged usually back in the panel next to a grounding rod. You can't do that on a boat because the electrons coming in on the hot wire may not be forced to leave the boat/dock area on the white neutral wire and leave via the boat's ground system (thru hull fittings, grounding plates, engine block, etc.). Everything will still work... like in your house... but you can kill someone if they get in the water next to your boat as the electrons are finding ground through a thru hull and the water and not going back through the dock connection. In your case, it will trip the GFI on the dock... However, a regular shore power connection will probably work just fine even though there is a problem with the wiring on this circuit...

Find it... and fix it... If your neutral circuit and ground circuit are bridged on the boat (via the wiring or a household appliance) and you hook up in a reverse polarity mode, someone will get electrocuted. Even if you are not in reverse polarity mode, someone getting in the water or providing an "easier path to ground" (like working in the engine room) will get electrocuted.

Yep... that's why you need to make sure that "Home Depot Special" fridge is wired for a boat and not for a house... and why every AC plug on a boat should be on a GFI circuit so if you plug in some dumb hairdryer, drill, heater, etc. that bridges ground and neutral, it'll pop the GFI on the boat and not light up the green ground circuit and water instead of going back to the dock via the shore power.

 

[jrcinnh]

If this has been working fine and then just stopped, first thing to do is replace the GFI outlet. They don't cost much and they fail pretty regularly, especially in a damp outdoor location. I buy them in packs of three from Home Depot for the house.

 

[Four Suns]

I've seen plenty of GFI plugs go bad (and that may be the case here), but I've never seen one that was "selective" on working depending on what was plugged into it... Doesn't hurt to replace it though... never know...

 

[floriduramax1]

These things are not that hard to find if you know what you are looking for. A GFI plug and a circuit breaker perform two very different functions and a short (like connecting the hot and neutral together) will not necessarily pop a GFI unit. You can blow a breaker and the GFI can still be engaged. A breaker pops when enough heat is generated inside the breaker from an overload condition. A GFI plug/unit does not look at overload conditions but monitors the current coming in on the hot wire (black) and the current leaving on the neutral wire (white). If the electrons coming in and going out don't match, the GFI will pop. This can happen on a boat from improper wiring or installing a household appliance on a boat that bridges the grounded neutral (white) with the ground (green). You can do that in your house (you shouldn't but manufacturers do... like on that 2003 vintage clothes dryer I have) but not on your boat. The GFI basically looks for electrons/current finding ground other than where you want them to (i.e. the white neutral wire) and this can happen without ever producing an overload situation that will pop a breaker. How this is designed in a land-based house versus a boat is different....

Look at this diagram:

The one thing you need to look for on that lighting circuit is if any of the switches or connections behind the panel have connected the white neutral line to the green ground line.... or if a green ground line has come lose and is touching a white neutral line... Or if you have plugged ANYTHING into a plug on that circuit (like a small appliance, hair dryer, toaster, etc) that is bridging green ground to white neutral.

In your house, the white neutral and green ground are bridged usually back in the panel next to a grounding rod. You can't do that on a boat because the electrons coming in on the hot wire may not be forced to leave the boat/dock area on the white neutral wire and leave via the boat's ground system (thru hull fittings, grounding plates, engine block, etc.). Everything will still work... like in your house... but you can kill someone if they get in the water next to your boat as the electrons are finding ground through a thru hull and the water and not going back through the dock connection. In your case, it will trip the GFI on the dock... However, a regular shore power connection will probably work just fine even though there is a problem with the wiring on this circuit...

Find it... and fix it... If your neutral circuit and ground circuit are bridged on the boat (via the wiring or a household appliance) and you hook up in a reverse polarity mode, someone will get electrocuted. Even if you are not in reverse polarity mode, someone getting in the water or providing an "easier path to ground" (like working in the engine room) will get electrocuted.

Yep... that's why you need to make sure that "Home Depot Special" fridge is wired for a boat and not for a house... and why every AC plug on a boat should be on a GFI circuit so if you plug in some dumb hairdryer, drill, heater, etc. that bridges ground and neutral, it'll pop the GFI on the boat and not light up the green ground circuit and water instead of going back to the dock via the shore power.

Good info here! In short, GFCI's measure and trip on voltage differential between hot and neutral, hot and ground and neutral and ground. Just wait till you trip one while using two way RF radios!! The newer GFI's are very sensitive.

 

[Four Suns]

I thought the voltages were from the induced current from a sensor on the hot and neutral...

Everything one wanted to know about a GFI:

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/gfi3.html#c1

A nice discussion of GFI and operation... note at the end of this article he discusses why plugging an RV shore power into an GFI is not always going to work... He calls it a "nuisance" but I disagree as a "water based" RV is sitting in a big medium that conducts electricity whereas a land based RV is sitting on rubber tires.

http://personal.cha.bellsouth.net/cha/j/o/johngd/files/rv/gfi.pdf

I did note he said there can be RF leakage on the wires that will trip the electronics on GFI plugs from 12v converters (he called it a "common problem")... Have you tried plugging in your boat on the shore power and leaving the converter off and see if that stops the problem?

 

[skibum]

I have used this hoockup and never had a problem before

Define "this hoockup" for us.

"This hoockup" as in your shore power cord, the pigtail adapter, and a GFI outlet on a dock.

OR

"This hoockup" as in your shore power cord, the pigtail adapter, and this GFI outlet on this dock.

Might just be a bad GFI outlet. Try a different one. Someone else may have used that GFI after the last time you did and fried it by doing something stupid as Gary mentioned. Again, try a different one.

Whats a "hoockup"?

 

[Four Suns]

I actually carry a couple GFI plugs as spares on the boat as I've had one go bad in the middle of a trip... The electronics inside these things seem to be sensitive to voltage surges... or saltwater.... or something.... Probably some sqrt(2) thing the engineers forgot about.

 

[floriduramax1]

I thought the voltages were from the induced current from a sensor on the hot and neutral...

Everything one wanted to know about a GFI:

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/gfi3.html#c1

A nice discussion of GFI and operation... note at the end of this article he discusses why plugging an RV shore power into an GFI is not always going to work... He calls it a "nuisance" but I disagree as a "water based" RV is sitting in a big medium that conducts electricity whereas a land based RV is sitting on rubber tires.

http://personal.cha.bellsouth.net/cha/j/o/johngd/files/rv/gfi.pdf

I did note he said there can be RF leakage on the wires that will trip the electronics on GFI plugs from 12v converters (he called it a "common problem")... Have you tried plugging in your boat on the shore power and leaving the converter off and see if that stops the problem?

:smt115

 

[rondds]

these things seem to be sensitive to voltage surges... or saltwater.... or something

That's b/c you bought them at Home Depot.

 

[tec10]

Gents- Thanks for the many suggestions. This forum is excellent, and you have been most generous with your knowledge. I will be investigating further this weekend based on your ideas.

To answer a few questions- the "hook-up" I was referring to was my having tapped into shore power in this very same way, at this very same spot and outlet before, without incident.

The fact that the issue seems isolated to that one specific circuit (I can run ac, use fridge etc. without tripping the GFI) leads me to believe that it is indeed a loose wire somewhere in the box, and not a problem with the GFI itself.

I will ask two follow ups:

- I am on the hard now, and can hook up to an outlet at my house (actual summer bungalow) which is NOT equipped with a GFI. Does this pose any risk to the bungalow or boat? my concern is that the GFI sent me a loud "stop what you are doing" message, and I don't want to do anything stupid.
- In terms of finding the problem- might it be sourced in the panel, at the switch, or at the light fixtures themselves? Could any one of these present the problem? In other words, could a problem anwhere in the circuit cause the entire thing to trip the GFI?