Shock from waste pump out fitting

[oldhudson]

Last week when getting pumped out the dockhand received a shock from the deck fitting. Using a meter I read 76 volts at the fitting to ground. I turned off all breakers one by one looking for the culprit but even with the onboard disconnect off it was still there. Only when I disconnected the 50amp power cord from the pedestal did it go away. How can I track the source? 76 volts but low amperage. I probably need to check the amperage next. Suggestions?
Thanks Jim

 

[Capt. Jon]

Ground / bonding wire? Follow it back to its terminal point. I would also check other grounding / bonding points.

 

[Bacchus]

...even with the onboard disconnect off it was still there.
Only when I disconnected the 50amp power cord from the pedestal did it go away.
How can I track the source? 76 volts but low amperage. I probably need to check the amperage next. Suggestions?
Thanks Jim

Jim

Main breakers interrupt hot & neutral but not ground.
Have you checked shore power pedestal and cord (connected to pedestal but disconnected from boat) neutral to ground?

Another way to verify might be to run onboard gennie (if you have one) w/ shore power cord disconnected.
If the 76V is not present it points to the shore power pedestal or cord.
If 76V is present there is something aboard (prior to the breakers) leaking to ground.

You don't mention if you have an inverter or isolation transformer or not...

Also note: Nigel Caulders "Boatowners Mechanical & Electrical Manual" is a worthwhile reference and walks you through testing grounding circuits w and w/o isolation transformers

 

[bayview]

A good possibility is corrosion in the shore power connectors. That causes a high resistance short between the wires. It could also be the dock pedestal. With everything off see if there is any continuity between the terminals on the shore power cord or just open the cord and look for corrosion.

 

[Larry M]

I'd hire an ABYC Certified Electrical Technician. Have him (her) go through the shore and vessels powers systems including the bonding. Besides an immediate safety issue you could also have a bonding issue that could be eating up some of your unwater hardware. We had a corrosion analysis done a few years ago, including travel time, it took less than 2 hours.

 

[oldhudson]

Thank-you for the replies so far. I will work on them when I get back to the boat. I agree about the corrosion issue too and I'm thinking a boat electrician might be worth his freight. Presently have no inverter but do have an onboard genie 21KW.


Drift Away
Ocean Alexander 545
Charleston SC

 

[FF]

The neutral is probably hot , perhaps from a mis wired boat on the dock.

Use a VOM and see if there is 75v between the white wire and the green wire.

 

[oldhudson]

Finally did some more testing today. There is still 76 volts at the pump out fitting with the shore power connected and on. With the shore power disconnected and the generator on and connected there is .25 of a volt. I had the admiral turn off the shore power and switch to gentry power while I held the leads to the tester in the same position. It was clear when the shore power was disconnected. I tested the shore power pedestal neutral to ground .25 volt 126 and 127volts on the two legs to neutral. I have a cablemaster so I tested the leads at the end of the shore power line and the results were again .22 volts ground to neutral and 126 and 127 hot to neutral.
I do have a residential oven and cooktop and will disconnect those tomorrow as I have heard that the sometimes bond ground to neutral on these appliances and this could?? Make my ground hot?? Not sure but Nigel Caldwell spoke about this in his book. Had a diver today clean the hull and the zincs all needed to be replaced in 6 months time. I'm sure I have underwater stray current happening too.

More tomorrow. Happy Thanksgiving all.



Drift Away
Ocean Alexander 545
Charleston SC

 

[Capt.Bill11]

The current pretty much has to be getting to the fitting via the bonding wire. Have you metered other binding wires?

 

[kthoennes]

When I saw he title of this thread I wasn't thinking electrical, I expected to hear a story about some shocking event with a marine sanitation system. I still remember the giant holding tank gas burp on the old Carver at 3:00 a.m. as I was struggling to clear bits and pieces of old joker valves plugging the discharge line. I did my best to clean everything off the ceiling but I may have missed some - my glasses were pretty smeared. My Robin Williams moment in the movie RV.

 

[TDunn]

As said above the only current path to the pump out fitting is the bonding wire. I see no reason to bond a deck fitting. So to make the pump out safer, remove the bonding wire.

Of course, you clearly have some issues with your shore power grounding system that need to be dealt with immediately. You do need to check over the shore power grounds to find out where the current is getting from shore power to the grounding system. If you have that much voltage at the waste pumpout fitting and it is bonded and your thru hulls are also bonded, you have the same voltage at the thru hulls. That can cause significant galvanic corrosion of those thru hulls quite quickly.

 

[bayview]

A low voltage like that most probably is a corrosion short. The most likely place for that still remains the power cord. Did you open the plug???

 

[oldhudson]

Bayview. Both the plug and receptacle are new and there are no signs of corrosion or either one. I have a marine electrician coming by this morning. More news later. Again there is no voltage between neutral and ground at the plug (power pedestal) or the terminals after the cablemaster in the boat.


Drift Away
Ocean Alexander 545
Charleston SC

 

[bayview]

any voltage at the cable dock end?? Who installed the new ends and why?

 

[rwidman]

The best advice so far in this thread is to hire a marine electrician. Electricity is a little too complicated for a web forum. That 76 volt reading is meaningless because no current is being drawn (except by the meter itself). And of course, how did a pumpout fitting get connected to the electrical system?