Mistyfying Electrical Issue

[egaito]

Mystyfying Electrical Issue

Forgive the play on words....

I'm trying to track down an electrical issue on the boat that seems to be relatively new and am running out of ideas. It's a bit of a long story, but I'm hoping the clues will
help generate some fresh ideas as I'm out of them.

I'm helping a guy out that is developing an ELCI test rig for power leakage between the boat and pedestal. So before taking him on as a client, I wanted to see what he had. I plugged it in between Misty and the dock, and to my surprise, it alarmed immediately. I tried it on the other cord with the same result.

Next we clamped the shore power cords (two 30 amp cords), which should read 0. Instead, I got a reading of several amps, the same reading on both cords and now I'm getting really concerned.

To make sure the boat wasn't a danger to anyone, we put a probe in the water around the boat, and even touched the running gear. Thankfully, there is no voltage going into the water. Apparently the grounding system is doing it's job.

Here are the other clues I'm working with:

The amperage I'm reading from both cords is directly proportional to the total load on the boat. Somehow the issue is crossing between the panels.

If I turn everything on, (stove, oven, AC, Hot water, etc) to load up the system, both dockside breakers pop simultaneously at about 28 to 30 amps. This is a first for me...I've overloaded on or the other at times but have never experienced anything like this.

I've tried turning off individual circuits to see if I could isolate a bad appliance. No luck there. The load goes down (indicating the circuit is going offline) but I can never get to a 0 reading on the clamp meter.

I've tried turning off the main breaker on each panel individually. The numbers get smaller as expected, but the current doesn't go away.

No new appliances have been installed

The onboard GFCI's never trip.

The cords and outlets do not heat up.

This isn't original Hatteras wiring. The boat was refit in the mid 90's. All has been well until this
year.

I have noticed over the course of the past year or so that AC light bulbs don't last as long....just attribbuted that to quality issues until now. Now I'm suspicious of everything.

Has anyone experienced anything like this? Any clues as to where to look next? Are the two panels supposed to be connected in some way?

Thanks,

 

[Pascal]

I thought you couldn't use a clamp on amp meter on shore power cord because it has to be clamped on a single wire? Never tried it

A 30amp breaker tripping at 28 to 30amp may be a little tired but at least it s doing it s job. Are you sure you were only pulling 28amp and not a little more?

 

[egaito]

If you clamp a cord, it shows the difference of what's flowing through the conductors. The reading should be 0, or under 30ma under normal conditions.

Blowing one breaker is normal. Both of mine blow simultaneously which is why I think my panels are somehow linked together.

I'm working on tracing wires but it's slow work with my back out. If I clamp the ground individually behind the input socket, I'm getting a small reading. For example, I just clamped the black (hot) which reads 0. The white (neutral) fluctuates around 7.4 amps. The Green (ground) reads .16 amps.

This is making my brain hurt.

 

[davidwigler]

I assume you have two 30 amp 120 volt cords. Do you have any 240 volt appliances aboard? Stove or water heater?

Do you have an isolation transformer that combines the circuits for 240 volts?

What happens when you turn off the main breakers in the boat and clamp the cords?

 

[egaito]

I assume you have two 30 amp 120 volt cords. Do you have any 240 volt appliances aboard? Stove or water heater?

Do you have an isolation transformer that combines the circuits for 240 volts?

What happens when you turn off the main breakers in the boat and clamp the cords?

You are correct on the cords. Breakers off, there is no reading.

I'm going to check the stove/oven to see if it's 220. Everything else is 110. I was talking with my AC guy on the dock this AM and that came up. There is a breaker on one of the AC panels for the stove, but not on the other panel.

 

[Pascal]

I don't think you d have any 220v stuff like a stove with twin 30amp cords as they d be no way to be sure they are on opposite phases. That's why when connecting to 30 amp outlets with a 120/240-50 cable you need a smart Y which will only let power thru if the twin 30s are on opposing phases.

The only link between both legs should be a common ground bus, and probably a common neutral bus. There is no way the hots can be linked together.

 

[egaito]

I started searching around tripping of ELCI breakers that are used in marinas in Europe and found an article about just such a situation. According to the article, I have a "false ground" somewhere on the boat (emphasis is mine):

The best way to take this measurement is to turn on your AC appliances one by one and see if the reading changes, just like the electrician in Guadeloupe had me do. If you get a reading that keeps going up as you turn on appliances, then you have what is called a “false ground” whereby there is a neutral to ground connection (common in land-based electrical connections) either at the panel board or at an appliance that should not exist.

Here's the article for anyone interested: http://www.caribbeancompass.com/leaking_boat.html

Now I just have to find it!

 

[Pascal]

I started searching around tripping of ELCI breakers that are used in marinas in Europe and found an article about just such a situation. According to the article, I have a "false ground" somewhere on the boat (emphasis is mine):

The best way to take this measurement is to turn on your AC appliances one by one and see if the reading changes, just like the electrician in Guadeloupe had me do. If you get a reading that keeps going up as you turn on appliances, then you have what is called a “false ground” whereby there is a neutral to ground connection (common in land-based electrical connections) either at the panel board or at an appliance that should not exist.

Here's the article for anyone interested: http://www.caribbeancompass.com/leaking_boat.html

Now I just have to find it!

Guadeloupe runs under French standards and over there the N and G are never connected, always two separate systems.

On a boat the N to G will not be affected by turning the appliance on or off, or even the breaker which only controls the H.

Some appliances bond N to G, I know my stove came that way and I wonder about the fridge.

And make sure that your Genset is completely disconnected, not just the hot as G and N is usually connected on the generator. The rotary should take care of disconnecting the neutral from the genny but since you said the boat was re wired, maybe they used single pole breakers with safety slide and your genset always leave N and G hooked up

 

[davidwigler]

Inverters are also designed to connect neutral to ground.

What about isolation transformer(s)? If both cords feed one transformer that could explain it.

Do the current readings on the two clamped cords cancel each other out? If so there is nothing going into the water.

 

[davidwigler]

Great video on topic:

http://www.youtube.com/watch?v=O7-s_mdEPb0&feature=youtu.be

 

[egaito]

Inverters are also designed to connect neutral to ground.

What about isolation transformer(s)? If both cords feed one transformer that could explain it.

Do the current readings on the two clamped cords cancel each other out? If so there is nothing going into the water.

If you mean are they equal, yes.

Readings from the water, and 0 readings contacting the prop and strut give me some confidence that there's nothing in the water at the dock, but who knows on genset power.

I have found what I believe is a tie between the ground bus and the bonding system, but I'll have to crawl around a bit more to confirm that.

A bit more data to ponder: On one panel, from the neutral to ground, 1v. From the hot to ground, 122v. Between the neutral and hot, 121v. These panels are exchanging power somehow.

 

[jim rosenthal]

Isn't the hot supposed to be 120v with respect to the ground, and the neutral also 120v with respect to the ground?

 

[egaito]

Isn't the hot supposed to be 120v with respect to the ground, and the neutral also 120v with respect to the ground?

My understanding is that any voltage between neutral and ground is "leakage" from somewhere. I read that on the internet, so it must be true

So far, I can not find anyone local that can be called a "marine" electrician. The closest I can find is a good marina electrician. If I can't find this on my own, that will have to be my next step.

 

[Pascal]

Inverters are also designed to connect neutral to ground.

Only when inverting, in charge mode they release the bond

 

[egaito]

I'm going to try a couple of things today:

With the power off, take each ground off the bus and ohm out neutral to that wire. My thinking is that I should see a high value on the ground wire of the offending circuit.

If that doesn't work, I'll try disconnecting each again and turn on the breakers and see which one gets rid of the current. I'm thinking I should do this with all of the individual breakers shut off as when I find the right wire, there will be no path to ground with it off of the bus. Makes sense to me....am I missing something?

 

[egaito]

Anyone recognize this?

I found this device behind one of my panels. A wire ran from the Neutral input on the rotary gen/shore switch through this device, to the grounding bus bar.

I disconnected it hoping that perhaps it had failed connecting neutral to ground in some way, but alas, I still have a path between them with this thing offlline.



As for progress on the search, I have isolated one green wire that has continuity to neutral. The bus is clean with this wire off. Though I'd nailed it until I started tracing the wire. Using the ohm meter and a long piece of jumper wire, there was no continuity between the end at the bus bar and the battery charger's ground wire. There IS continuity between this end and the hot water heater case. Great! Found it, right! Not so fast....

I disconnected the wire at the water heater. The case is now "cold" and the wire is "hot" (in the sense that there is continuity back to the end at the panel. While doing this, my jumper wire touched the motor mount and there was continuity there, between the end at the panel and the mount. So now I'm really confused, and it gets even better.....the water heater is on the other panel.

 

[Fanfare]

The square thing with the red label is your reverse polarity alarm. Buzzes if hot and neutral are reversed. Should be one on each leg of your incoming 110v. wiring inside the panel.

 

[egaito]

The square thing with the red label is your reverse polarity alarm. Buzzes if hot and neutral are reversed. Should be one on each leg of your incoming 110v. wiring inside the panel.

Thanks Jim. I've only heard that go off once since I've had the boat. never figured out what caused it, but it was years ago.

This is behind the original Hatteras panel. The other, newer panel has a light on the breaker.

I traced the wire that showed continuity from neutral to ground and found it was an outlet box in the ER, into which my ice maker is plugged in. Unplug the ice maker, continuity goes away. Simple enough, but upon attaching everything back onto the bus, once again I have continuity, so apparently there is more than one issue going on here.

A question about the ice maker: When I unplug the ice maker, and test across the three prongs of the plug, what should I see? I get continuity between hot and neutral, but not between the round prong and either of the other two. This doesn't make sense to me considering when it is plugged into the boat's system, I do get continuity between ground and neutral.

 

[bobk]

There is a real good marine electrician in Stuart, FL but that may be too great a distance for you. Trinity Electric. I can look up his contact info if you want it.

Bobk

 

[MikeP]

I have found what I believe is a tie between the ground bus and the bonding system, but I'll have to crawl around a bit more to confirm that."

That is the correct configuration. The ac ground (green wire, NOT THE AC NEUTRAL), the dc ground and the bonding system are all connected.