Grounding or bonding issue???

sanjuanjohn · Oct 12, 2014

Ah, sorry for the confusion I see what you're saying. I don't have an adapter as there are so many different sockets I always just open the j-box (with the cord plugged in) and test at the breaker.

Delfin · Oct 12, 2014

ksanders said:
With your shore power disconnected, and your inverters, and generators output isolated, use an ohm meter between your AC neutral and ground.

You should see an infinite reading.

If you do not you need to find and resolve the issue.

This has always seemed the simplest and most accurate way of checking for leakage. Any decent voltmeter measures milliamps, correct?

KS, when you say that the inverters and gensets are "isolated" please clarify precisely what you mean... thanks!!

psneeld · Oct 12, 2014

If you had a hot wire rubbed through the insulation that contacted any of the bonded or DC grounded systems and it was going to ground...would that show up on the Neutral to Ground test???

ksanders · Oct 12, 2014

Delfin said:
This has always seemed the simplest and most accurate way of checking for leakage. Any decent voltmeter measures milliamps, correct?

KS, when you say that the inverters and gensets are "isolated" please clarify precisely what you mean... thanks!!

What you are checking for is a neutral to ground short. This would create two parallel paths for what should be neutral current. One path is as it should be, from your loads to the boats panel, then out to shore power, over the neutral conductor. The other path, the one you do not want is from your loads, through ground, and sea water, back to shore power. (your shore power feed from the dock has its neutral shorted to ground and the ground conductor connected to earth ground)

Using the ohm meter is a very quick easy way to check for this. On the AC panel with no power to it you should see infinite resistance between ground and neutral.

You need to isolate the generator and inverter to do this. Thats because at the generator its neutral is connected to its frame, which is grounded. This is the only way, when running on generator power your ground actually does any good. Thats why your generator selector switch needs to disconnect both the hot and the neutral from the generator.

Your inverter/charger works kinda the same way. When AC is present at its input the neutral to ground is not shorted by the inverter. When the inverter is in invert mode (no AC present at its input), it automatically shorts neutral to ground, so that your ground actually is effective.

This all makes sense if we remember the job of the ground conductor. Its whole function is safety. The metal parts of your applicances are connected to the ground conductor. If there is a short in your appliance from hot to any metal part, the ground conductor provides a path for the current so we do not get electrocuted when we touch it.

psneeld said:
If you had a hot wire rubbed through the insulation that contacted any of the bonded or DC grounded systems and it was going to ground...would that show up on the Neutral to Ground test???

If you had a hot to ground short, it would most likely operate the circuit breaker or start a fire. To test for a hot to ground, you could also take an ohm meter reading. Hot to ground should be open. Hot to neutral will of course show your loads. I've honestly never seen a hot to ground short in a properly grounded system that did not operate the circuit breaker.

psneeld · Oct 12, 2014

ksanders said:
cut for space.....

If you had a hot to ground short, it would most likely operate the circuit breaker or start a fire. To test for a hot to ground, you could also take an ohm meter reading. Hot to ground should be open. Hot to neutral will of course show your loads. I've honestly never seen a hot to ground short in a properly grounded system that did not operate the circuit breaker.

Thanks...

I have read and seen examples that I thought were this....maybe not...I'll have to do a little looking but boat breakers are notorious for being squirrely about tripping.

Delfin · Oct 12, 2014

ksanders said:
What you are checking for is a neutral to ground short. This would create two parallel paths for what should be neutral current. One path is as it should be, from your loads to the boats panel, then out to shore power, over the neutral conductor. The other path, the one you do not want is from your loads, through ground, and sea water, back to shore power. (your shore power feed from the dock has its neutral shorted to ground and the ground conductor connected to earth ground)

Using the ohm meter is a very quick easy way to check for this. On the AC panel with no power to it you should see infinite resistance between ground and neutral.

You need to isolate the generator and inverter to do this. Thats because at the generator its neutral is connected to its frame, which is grounded. This is the only way, when running on generator power your ground actually does any good. Thats why your generator selector switch needs to disconnect both the hot and the neutral from the generator.

Your inverter/charger works kinda the same way. When AC is present at its input the neutral to ground is not shorted by the inverter. When the inverter is in invert mode (no AC present at its input), it automatically shorts neutral to ground, so that your ground actually is effective.

This all makes sense if we remember the job of the ground conductor. Its whole function is safety. The metal parts of your applicances are connected to the ground conductor. If there is a short in your appliance from hot to any metal part, the ground conductor provides a path for the current so we do not get electrocuted when we touch it.

If you had a hot to ground short, it would most likely operate the circuit breaker or start a fire. To test for a hot to ground, you could also take an ohm meter reading. Hot to ground should be open. Hot to neutral will of course show your loads. I've honestly never seen a hot to ground short in a properly grounded system that did not operate the circuit breaker.

Much appreciated.

LaBomba · Oct 13, 2014

Wow, great information. I have just moved houses so been busy a few weeks. The boat is on the hard now for the winter. This problem started before the bow thruster was installed and I don't have either an inverter or a generator, everything is 12v. Do have an anode on the shaft and metal extension of the keel for the rudder support. If I hook my generator up to the boat would I be able to test this on the hard or do I need to be in the water? Or could the problem be with the marina shore power plug? My dock neighbours do not have the same issue. I really want to solve this issue for both the sake of safety and potential harm to the boat. BTW, there does not seem to be any corrosion just a thick extremely hard calcium magnesium like hardness buildup, like over an eighth of an inch thick. You can't even scrape it off, it takes acid which quickly dissolves it. Thanks all for your help!!

LaBomba · May 30, 2016

Well just an update on this old post as I have recently just resolved the electrical problem after many attempts. Actually the marine electrician found a couple issues after an exhaustive search. The PO the year before I bought the boat had a new battery charger installed and did not direct wire it but had a plug installed in the ER. Well turns out the plug was wired by some moron with the wires reversed, reverse polarity, problem one. This somehow screwed the new battery charger and the electrician found while going through each circuit and using the silver silver chloride probe in the water, that when the battery charger would kick in, 6 to 7 volts were reading from the DC boat ground to the water. This was not causing any corrosion but was actually attracting minerals in the water to attach to the metal parts of the running gear. Waiting on a new charger and hope this all goes away and I can do the happy dance.

boatpoker · May 30, 2016

djmarchand said:
Let me give it a try:

AC current from the shore power outlet goes down the black wire (I am using DC terms but bear with me) to the various appliances on the boat and then back up on the white (neutral wire). If you have any kind of fault- a short to ground in an appliance or wire then the current comes back on the green- the ground wire.

If you put an AC clamp on ammeter around all three wires you should see zero amps. The incoming black cancels out the outgoing white (or green).

But if you have a leak to the water (typically in the bilge) then some of the current will leave the boat through the water and there will be less current in the white or green wire and your clamp on ammeter will show some current.

It is a crude but effective test for AC leaks to the bilge.

But having said all of the above, AC leaks to the bilge don't cause what you are seeing. And I am not sure it is an electrolysis issue at all.

David

If you have current in the green you have an even more serious issue and one that is potentially lethal. You shouldnot see current in the green.

Grounding or bonding issue???

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