Ground Fault Issues when Plugging into New Marina System

[Tlynch99]

Hello,

I experienced something new at the end of last season. We went to a Marina, planning to stay overnight. This marina was recently updated to the latest in "show power" stuff... (not really sure what that means). Anyway the Marina staff came out and wanted to test our boat before allowing us to plug into the Shore Power. They wheeled a cart over, and explained that this cart would be plugged in-line with the show power and my boat. Basically they said it would test if the boat was leaking any current into the water. Ok seemed to make sense. Anyway to make a long story short, my boat failed miserably and we weren't able to plug in. They said we were leaking over 200mA into the water. Our boat's a 1992 SeaRay 330 Sundancer, Twin 7.4, AC, and Kohler 5K Genset.

Has anyone else experienced this new type of Marina System, and know how to diagnose this type of failure?

The exact process they followed is outlined below:

- Asked us to turn off all breakers on the boat, both main and individual breakers.
- Brought cart over, and plugged it in-line with the #1 outlet (Not the AC one) on our shore power, we were using our shore power cable.
- Asked us to then turn on the main breaker, we did so, and the tester immediately tripped. Hmm ok that's not good.
- Then we tried the AC outlet. Same result immediately tripped the testing machine when the main breaker was switched on.
- When then tried my backup shore power cord. Same results...

Any help diagnosing this would be greatly appreciated.

 

[ttmott]

Some older boats do not switch the power neutral legs when switching between shore-power and generator power. As generator neutrals are common with the ground and bonding system on the boat the shore-power neutrals then are tied to the boat's bonding system if not switched. As the neutral is the return path for the hot side of the power there then will be an imbalance between current measurements made at the shore power interface (some of the current is leaking through the bonding system to the water and if high enough back through the shore power grounding). Current follows the least path of resistance. In your case it appears that there is a 200ma imbalance between the shore power interface hot and neutral.

It appears the new "showpower" is GFCI protected which for a boat that is leaking current to the water or back through the system ground the GFCI will trip. A GFCI protection system simply measures the differential between the Hot and Neutral legs; if the current on both legs is not the same the GFCI will trip.

This can be a safety issue if there is a fault on the boat for those in the water so if your boat does not switch both the hot and neutral legs on the generator transfer switch you should consider upgrading.
Tom

 

[paulswagelock]

Does your boat have a galvanic isolator on the ground wire inlet from shore power? New standards require it, and it prevents leaking current into the water to earth.

 

[ttmott]

Does your boat have a galvanic isolator on the ground wire inlet from shore power? New standards require it, and it prevents leaking current into the water to earth.

Paulswagelock - not really; the isolator prevents low level current from passing from shore side ground through the boat's bonded metal elements and to the water thus preventing galvanic corrosion to the boats wetted metal elements. This circuitry has nothing to do with the issue the OP is dealing with on the GFCI dock power installations of late other than all boat generators tie ground and bonding to neutral.

 

[paulswagelock]

I didn't read anywhere that the marina was testing for a ground fault, I think the OP just assumed that??? My marina checks for current leakage into the water posing a hazard to other boats or danger to people in the water. They don't check for ground faults. So in my case, they are checking to see if you have any wiring faults or a failed isolator.

 

[bahamabreisus]

Oh my god, what will they come up with next. Most power leakage comes from the marina itself.

 

[PlayDate]

Frankly, I still don't know what "show power" means. I agree with Tom that if they plugged the boat into some portable device and it clicked off when they turned the master breaker on it sounds more like a ground fault issue. The OP said that the device was testing for current in the water which is confusing because the power would need to stay on to get a reading.

Anyway.....it sounds like we need a picture of "show power" to solve this mystery.

 

[ttmott]

Frankly, I still don't know what "show power" means. I agree with Tom that if they plugged the boat into some portable device and it clicked off when they turned the master breaker on it sounds more like a ground fault issue. The OP said that the device was testing for current in the water which is confusing because the power would need to stay on to get a reading.

Anyway.....it sounds like we need a picture of "show power" to solve this mystery.

Yes, when there is a difference in current between the white "neutral" and black "hot" wires at the boat's shore power interface the current must be leaking somewhere else like to the water around the boat or back through the ground leg in the shore power connector.
All AC power systems if working correctly have exactly the same current flowing through the hot and neutral conductors. If they don't there is a leak or fault.

Only at the primary utility panel do the neutral wires of an AC power network tie to the ground system. When the boat is not connected to shore power and switched to generator power then the generator is the primary utility panel and the neutral wires are tied to the ground and bonding network; this is why it's important that both hot and neutral wires are switched in the transfer switch.

Marinas are transitioning to GFCI power systems primarily for insurance reasons. It is, however, a good thing as that will weed out the boats that have problems with faulty power systems and causing issues with adjacent boats and be a much safer environment.

 

[Ike]

Your boat probably has a ground fault somewhere in the AC electrical system. However, it will take hiring a certified marine electrician to diagnose it. You may well be leaking current into the water, but to be sure someone needs to do a test that actually measures the amount of current in the water. I have never heard of "show power" Are you sure they weren't just saying shore power? But it is probably someones proprietary name for a system to measure the current in your shore power connection. Anyway as has been said if you measure the current going out and the current coming back, and there is a difference then it is leaking somewhere. This will not trip your circuit breakers or the GFCI on your boat (if it has one) It will trip a device called a Residual Current Device (RCD) which, if the RCD is installed at all it is installed in the marine shore power outlet on the dock. Not on the boat. They are common in Europe but not so common in the US yet.

A galvanic isolator will not stop this. A galvanic isolator is installed in the green wire (called the grounding wire, as opposed to the grounded wire) and only stops DC current from flowing, but permits AC to pass through. This helps to prevent stray DC currents in the water but does nothing about the AC.

 

[ttmott]

Your boat probably has a ground fault somewhere in the AC electrical system. However, it will take hiring a certified marine electrician to diagnose it. You may well be leaking current into the water, but to be sure someone needs to do a test that actually measures the amount of current in the water. I have never heard of "show power" Are you sure they weren't just saying shore power? But it is probably someones proprietary name for a system to measure the current in your shore power connection. Anyway as has been said if you measure the current going out and the current coming back, and there is a difference then it is leaking somewhere. This will not trip your circuit breakers or the GFCI on your boat (if it has one) It will trip a device called a Residual Current Device (RCD) which, if the RCD is installed at all it is installed in the marine shore power outlet on the dock. Not on the boat. They are common in Europe but not so common in the US yet.

A galvanic isolator will not stop this. A galvanic isolator is installed in the green wire (called the grounding wire, as opposed to the grounded wire) and only stops DC current from flowing, but permits AC to pass through. This helps to prevent stray DC currents in the water but does nothing about the AC.

Actually it is classified as GFCI. Article 555 of the NEC for marina installations provides for the Ground Fault device to be installed in the marina's primary circuit panel or individually at the shore power interface pedestals. Some marina's opted for the cheaper installation on the primary panelboard but are suffering the consequence of one boat having an issue taking out the entire dock or at least part of the dock. It puts owners at risk that are not near their boats and difficult to determine where the fault is located. If the marina has upgraded to GFCI make sure to select one where the GFCI is on the pedestal. The NEC allows only 100ma imbalance so it doesn't take much leakage to trip off line (1000ma + 1 amp). We are at an older marina which has not renovated to the latest NEC.

 

[PlayDate]

After digging around I found this:

http://acraelectricinc.com/wp-content/uploads/2014/05/Stray-Current-Tester-Brochure.pdf

It seems to operate consistent with OP's description. These guys filed a patent on the device in 2014 and it makes sense. It is known as a Stray Current Sensor and this is how it is used:

http://www.marinesurveypros.com/scs-stray-current-sensor/how-to-use-your-scs/

Seems you could make a living tracking down stray current and re-wiring boats!

 

[Tlynch99]

All,

Thanks for all of the replies on this. I suspect it's what tmott said regarding:

"Some older boats do not switch the power neutral legs when switching between shore-power and generator power."

Since the boat is a 1992, and the testing device tripped the minute I selected "Shore" on the main switch, I hope it's something this simple.

I guess I'll get a marine qualified electrician to come take a look, and do any upgrades needed.

Regarding what exactly the device was... it was pretty big, about the size of a shopping cart. I'll try to find a picture of it online somewhere.

The marina definitely knew about how much of a pain this process of testing the boat was... I was actually one boat in a group of 15 on a yacht club trip that were headed to this Marina. It took over 3 hours once all of the boats were tied up to finish testing each one. About 50% of us failed, ie not being allowed to plug into shore power. If you just ignored them and plugged in anyway you would trip a breaker further upstream and the whole dock would go dark. We were paying almost $5 a foot per night, and they definitely knew people would be upset that they couldn't plug in... because of this, they had a whole section of the marina where people could be in a slip, while running a generator...

The owners of this Marina own 3-4 more in the Massachusetts area and mentioned that this summer their other locations would be "upgraded" to this type of shore power (where there is a more stringent GFI requirement). I just hope they don't cheap out and put individual GFI's at each post. The boats that did pass the test, were frustrated because the whole pier they were on tripped twice during the night... shutting off AC's etc...

 

[villain style]

I think "Show Power" is an accent issue for "Shore Power".......

 

[Brite Idea]

I would get a marine electrician to go over your boat's electrical system. Don't mess around where electricity and water are concerned. Good luck and be safe.

 

[Ike]

I agree. AC is deadly especially around water. Let a Professional deal with it. But make sure you ask if they are ABYC certified. If not get someone who is.