Excessive amperage leak?

[diver dave]

Another boat just came into the marina and he hooked up two 30 amp cords to a 50 amp terminal via a Y cord. We put the Fluke 323 on the 50 amp side of the splitter....zero reading. Put the Fluke on each 30 amp cord and one reads about 65. amps, the other 7.1 amps (all ac components on the boat "on"). We then turned off components and the "leakage" reading on the 30 amp cords dropped to around 1.4 amp with virtually everything off. So, experts, what's going on??? By the way, we moved the 30 amp cords to other pedestals and saw the same thing (in other words we took the Y cord and the original power pedestal out of the system).

U saw 65 amps with probe around the entire cord?

 

[sdowney717]

Could definitely be a neutral to neutral shared bond going on there, a big no-no.
A GFCI would definitely trip off a circuit where multiple neutrals are returning power.
A GFCI is an honestly good way of monitoring and checking the integrity of your AC system, if it trips that means you may have a big problem with wiring or an appliance, or it could be something got sprayed with water and it needs to be cleaned off if salt water or just dried out if fresh water..

Honestly dont understand why anyone would object to improving their boats AC system by using ground fault technology. It will force you to make things right with the wiring, that otherwise you would ignore.

 

[CharlieJ]

BTW, in order to have AC leakage into the water column, there must be two faults in the system:
1. A line to ground fault, typically in a component and
2. A break or high impedance in the safety ground wire from the boat back to the source. In the case of shore power, the source is the secondary of the transformer feeding the dock.

Further to this discussion, the adage that “Electricity takes the path of least resistance” is not totally correct. AC takes ALL paths present back to the source of power. And therein lies the root cause of the problem.

 

[ksanders]

BTW, in order to have AC leakage into the water column, there must be two faults in the system:
1. A line to ground fault, typically in a component and
2. A break or high impedance in the safety ground wire from the boat back to the source. In the case of shore power, the source is the secondary of the transformer feeding the dock.

Further to this discussion, the adage that “Electricity takes the path of least resistance” is not totally correct. AC takes ALL paths present back to the source of power. And therein lies the root cause of the problem.

Yep!

 

[ksanders]

So is the boat leaking amperage or is it not possible to tell for sure given the interconnected neutrals?

Like others I do not think that your test method is the best.

I suppose it will catch the really big issues though.

That said, you indicated that there was a zero reading on the 50 amp part of the splitter.

so... if we stipulate that your test method is Ok, then you have no ground leakage, just a imbalance on two parallel 30 amp neutral paths.

 

[Rufus]

U saw 65 amps with probe around the entire cord?

That should have been 6.5 amps.

I'm still not clear as to why the two 30 amp cords would show fairly high amps on the fluke, even when hooked up to separate pedestals.

 

[sdowney717]

Yes AC takes as many paths as it can, however most of the current will flow on the path of least resistance, but even a little current on an alternate path can kill and I would think a small child would be more easily hurt or killed by what you might not feel as badly. Thicker drier skin has greater insulation to current.
A GFCI will keep everyone alive and well, how tragic it is when people are killed because of their faulty wiring unprotected by a GFCI. It will definitely ruin your day and or your life.

 

[CharlieJ]

Rufus #36
For 120VAC, current flows to a load on the hot conductor (L) and returns to the source on the neutral (N) conductor. If a load (branch circuit) supplied by SP #1 has its N wire on the SP#2 N buss, the load will work fine but the current supplied by SP#1 will be out of balance with the current being returned to SP#1 and the GFCI/ELCI/RCD will sense the imbalance and trip.

 

[sdowney717]

6.5 amp load imbalance even if no ground fault is really BAD.
Consider that the plug and wires are rated at 30 amps.

But your feeding extra amps coming back on a partially shared neutral wire. So if your drawing close to full loads, that neutral has to bear extra amps it is not designed to handle and the 30 amp breaker will never sense the over current and trip off.
You will burn up the plugs and overheat the wiring, maybe can cause a fire. Every connection has some resistance, sharing a neutral return, the connection with less resistance will be bearing the extra current, if it gets hot, well resistance can make things hot enough to catch fire.. Look at the toaster elements as an example, the high resistance wire element gets red hot. the wires can get hot enough that maybe the insulation breaks down, then you might get some sparking when the wires start shorting together and bad stuff is going to happen.

It is bad practice on branch wiring also to share a return path.
Can create all sorts of grief.
A GFCI or the ELCI will prevent all that bad stuff from happening, but you will have to fix the bad wiring, which is a good thing.

 

[syjos]

When i say Line to Ground shock hazards, I mean the same potential shock possibility is there, with or without the iso xfrm. Either way, if u grab a line conductor, your body will want to rise to that potential. On a piece or dry wood or a rubber mat, fine. But standing on a wet deck barefoot, there is trouble. The iso trans does not fix that, when it is wired per ABYC standards.

With an isolation transformer, earth is no longer the ground so grabbing a line will not shock you unless you have your floor connected to ground. Which is highly unlikely.

You'd have to grab a hot line and neutral or ground to be shocked.

 

[sdowney717]

With an isolation transformer, earth is no longer the ground so grabbing a line will not shock you unless you have your floor connected to ground. Which is highly unlikely.

You'd have to grab a hot line and neutral or ground to be shocked.

Or have a ground fault on the boat system. Pretend a hot is sending some current to a device with a ground fault on the boat, isolated from shore power with the transformer. The transformer is the power source, it is no different that any other high voltage power source. Since the ground is carrying some current with the ground fault and there is no GFCI to shut it off, the ground is live, has a higher voltage than it should, so if your body intercepts that power, you will be shocked, if touching either neutral or hot wire or even a better quality grounded device, your body providing a current path for current to flow. The isolation transformer ground is grounded itself to the boat grounds, so it is making a connection. who knows how good the grounds really are, are they corroded, that makes the shock potential worse. Maybe the ground on whatever has the ground fault is not even grounded at all, like the ground wire is not there or broken.

You know if everything is perfect, perfect wiring, perfect appliances, perfect devices, then most likely never a problem will occur, but most systems are not perfect and stuff just happens to fail whenever it does. It could fail by getting wet with rain or fresh or salt water, then you would have an unexpected ground fault, or if there is no ground wire a potentially serious ground fault..

I got shocked with a double insulated drill when drilling under a wet sink cabinet and I somehow touched a wire that was running to a small electric water heater, which was grounded. The drill got some sink water into it, and it shocked me. I am still not sure exactly why it happened, but it did. Maybe the wet wire conducted current on the outside of the insulation.
there was no GFCI on that bathroom circuit, house built in 1963. I thought I was safe cause the drill is double insulated, but water makes that of no effect. Jolted me enough I had trouble letting go of the drill trigger.

 

[diver dave]

With an isolation transformer, earth is no longer the ground so grabbing a line will not shock you unless you have your floor connected to ground. Which is highly unlikely.

You'd have to grab a hot line and neutral or ground to be shocked.

A bit difficult to follow that one. What does happen is the iso xfrm sets up a "boat ground" independent of the shore cord. The install does, however, connect all equipment grounds and DC-, engines, and likely thru hulls and the underwater metal bonding system to this "boat ground", ALONG WITH THE NEUTRAL. So, just like installs without the local transformer, shocks are still available to you.

It is possible to make a fully floating system off ground for power distribution, but that is not what ABYC (yacht) installs are. It is what military ships installs are.

 

[sdowney717]

Before I put a GFCI on the AC heat pump, one day I reached down to feel the discharge temp of the raw water for the AC unit. And I got a big shock, which shocked me, hah, funny.
So I opened up the control box on the cruisair unit, and found rain water had gotten into it, since, a water drain hole was clogged up and a hot AC power wire that runs to the raw water pump, since it was so low in the box and just happened to be a slip spade insulated connector there was soaking wet, and it was sending hot power into the ground of the unit, (so a ground fault had occurred) and that salt water from the pump was channeling it out with the flow back to shore power. So current was running from the ground of the AC unit, into the copper heat exchanger coil on top the unit and out with the water flow. Just me leaning over the side of the boat and touching the flow shocked me, so my body was somehow connected to the circuit. And I bet that was going on for a while too, without out anyone knowing about the current leakage. Everything about the unit was working fine, with the bad ground fault.
Probably my hand became part of the circuit when I stuck my hand inside the water flow. So it would not have killed me, but it was painful.

Where my boat is its brackish water.

 

[diver dave]

Ouch; sounds like the unit did not have an adequate ground installed. If the copper, etc was HOT, then there is a missing ground. No shock should have occurred, since this "leakage" would have a low resistance path back to the panel. If high enough, it would trip the breaker. BUT, water is the boogie here. If one just put a hot conductor just in water, it won't result in enough current to trip the branch, but will sit there eroding metal and wait for its moment to get you!

 

[sdowney717]

Ouch; sounds like the unit did not have an adequate ground installed. If the copper, etc was HOT, then there is a missing ground. No shock should have occurred, since this "leakage" would have a low resistance path back to the panel. If high enough, it would trip the breaker. BUT, water is the boogie here. If one just put a hot conductor just in water, it won't result in enough current to trip the branch, but will sit there eroding metal and wait for its moment to get you!

Even with a ground, current will flow multiple paths, You can feel a quite small amount of current. The way these units were setup, the ground is the copper tubing running from the unit to the evaporator. At the evaporator is the 3 knob control panel, and the ground wire is secured to the metal edge of the evaporator. It is a dual split system, with 2 remote evaporators, not a self contained AC unit. So there is no ground wire running from control panel to the unit. They saved wire costs that way. The ground is the copper tubing.

If the ground fault is way under the amps required to blow the breaker, then everything just seems normal, but there is a bad shock hazard just waiting to bite you and you dont have a clue.

A GFCI would detect that and shut down the power as soon as it happened to develop a ground fault. Really great safety technology they came up with.

I did have a shore cord get pinched and then the cord fell in the water after a big storm. I went back a week later and heard something hissing, the cable was hot, there was a tiny hole in the yellow insulation. When I cut it open, 6 feet of number 10 gauge wire had disappeared. Since the short was not enough amps to blow the breaker, it just happily kept sending power into the brackish water around the boat. There are good reasons not to swim around marina boats. An ECLI breaker on that dock would have shut off the power immediately.

It was a 50 foot cord, but not anymore, I cut off the bad part and it became a 35 foot cord. And I still use it today. I back the boat into the slip, and the connection for the power is at the stern. So 35 feet works fine.

 

[diver dave]

Yep. Bad ground design. A decent bonding system and there will be no tingles

 

[syjos]

All these on board shocking scenarios above would be prevented with a ELCI/GFCI on each circuit or whole boat in addition to an iso trans.

The isolation transformer performs it's stated purpose; preventing swimmer from electrical shock.

 

[diver dave]

Tomorrow, I will be asked to fix a melting stainless tube issue on a multi-MegaWatt transformer very far away. Here, the device in question is getting a "stray current" from the transformer, which should already be VERY well grounded to a sub earth ground grid. My piece of equipment is grounded through its power connection, but likely not to local earth. Unfortunately, I can't just say "put on a GFCI". Close to an entire city would switch off, LOL... Bonding is the primary solution to all of the above riddles. GFCI is a backup, when bonding is NOT right, or the situation is using non-grounded equip (double insulated), or a myriad of other, unforeseen issues occur, usually with humans.

Test your electronic protection devices frequently. Contacts weld shut, transistors short out, other bad things happen to the GFCI's. In my basement, a lightning bolt destroyed my last failed gfci.

 

[Rufus]

Well we had an electrician from the local yard look at the situation and he came to the conclusion that the two 30 amp circuits are somehow interconnected (same as some of you folks)...either at the neutral wire or possibly somehow via the shore/off/genset switch. And I still can't understand why we get an amperage reading with just one cord plugged in and the other unplugged...and why that wouldn't be an issue....maybe it's not as long as the phantom interconnect exists. Anyway, the electrician put a meter probe in the water next to the boat and it seemed OK. So we left the boat plugged in. This subject is beyond a novice like me to understand and even the electrician, who is a pretty bright guy was a little confused as to what was happening. We do know that this boat had a serious electrical short in one of the 30 amp onboard plugs last year...and we also know that the AC was an add on. But tough to trouble shoot a transient boat in a short time on a weekend.

I'm still not clear as to why interconnecting neutral wires on the two 30 amp panels is a bad idea....just trying to learn/understand...

 

[diver dave]

Load end neutrals that connect is bad. Overcurrent protection is only done on the Line side. The design assumes neutral current equals line current. Violate that rule and over currents will occur on the white wires. Further, any upstream ground fault devices wont work correctly. And lastly, opening a branch breaker wont stop its associated neutral with carrying lethal current. And, more lastly, eddy currents will be produced in steel wireways that cause them to heat.

 

[ksanders]

Tomorrow, I will be asked to fix a melting stainless tube issue on a multi-MegaWatt transformer very far away. Here, the device in question is getting a "stray current" from the transformer, which should already be VERY well grounded to a sub earth ground grid. My piece of equipment is grounded through its power connection, but likely not to local earth. Unfortunately, I can't just say "put on a GFCI". Close to an entire city would switch off, LOL... Bonding is the primary solution to all of the above riddles. GFCI is a backup, when bonding is NOT right, or the situation is using non-grounded equip (double insulated), or a myriad of other, unforeseen issues occur, usually with humans.

Test your electronic protection devices frequently. Contacts weld shut, transistors short out, other bad things happen to the GFCI's. In my basement, a lightning bolt destroyed my last failed gfci.

Hmmm

We have somewhat similar skillsets

It is interesting the people you run into here.

 

[diver dave]

Very cool[emoji847]. US or canada?

 

[syjos]

Branch circuit GFCI's are required by most marine insurance company's.

I do'nt think bonding would prevent someone from getting a shock from a faulty appliance. A GFCI will.

 

[sdowney717]

Well we had an electrician from the local yard look at the situation and he came to the conclusion that the two 30 amp circuits are somehow interconnected (same as some of you folks)...either at the neutral wire or possibly somehow via the shore/off/genset switch. And I still can't understand why we get an amperage reading with just one cord plugged in and the other unplugged...and why that wouldn't be an issue....maybe it's not as long as the phantom interconnect exists. Anyway, the electrician put a meter probe in the water next to the boat and it seemed OK. So we left the boat plugged in. This subject is beyond a novice like me to understand and even the electrician, who is a pretty bright guy was a little confused as to what was happening. We do know that this boat had a serious electrical short in one of the 30 amp onboard plugs last year...and we also know that the AC was an add on. But tough to trouble shoot a transient boat in a short time on a weekend.

I'm still not clear as to why interconnecting neutral wires on the two 30 amp panels is a bad idea....just trying to learn/understand...

The power going into a device should return on the same dedicated cable going out of a circuit, otherwise consider it stray current. It is straying from where it should be onto return wires where it should not be. That can overload the return wires capacity, ampacity, could cause it to overheat and maybe start a fire. And then the plug ends are also being overloaded with excess current, causing them to get hot and maybe burn. Its not a problem if the returning amperage loading is below the rated capacity of the wire, but its still bad practice, causes trouble you dont want to deal with, and can be easily prevented when the installations are being put in, why ask for trouble you dont need.

AND if you install ground fault breakers later on, you got a real mess trying to figure it all out, because the basic wiring was done wrong somewhere.

Another concern, that return wire like a neutral is unexpectedly LIVE with power when you have a shared neutral, You might think the power to that circuit is turned off, and not be careful and you could then be shocked, because hey, you thought it was dead, but who knows maybe you would be dead.
The neutral wire is a current carrying conductor, and it can shock as bad as the hot wire. Just disconnect it and put your body into the circuit on the neutral and you will find out how badly you will be shocked. Lots of people wrongly think a neutral conductor is safe, and it usually is as its ground potential is at zero if everything is properly connected.

But if your in a panel box and disconnect a neutral and you turned off its distribution breaker, but its neutral return conductor is shared with another circuit, and the circuit is running an appliance, then that neutral return conductor is live with power and you can be ELECTROCUTED. If that happens you can blame the lousy electrician who wired up your circuits, if your not dead.

 

[STB]

I've been mostly off grid recently and am just catching up on the Forum. This thread was a great read! (I popped onto the Forum only briefly earlier when I saw an engine specific thread title pop up).

Tangential question: Is it uncommon for a boat with 30A/120V service to have overcurrent protection on neutral at the on-boat 120V main breaker/disconnect?

Does the answer change if the boat has dual 30A/120V service? (In which case, there would be two breaker/disconnects)?

 

[sdowney717]

I've been mostly off grid recently and am just catching up on the Forum. This thread was a great read! (I popped onto the Forum only briefly earlier when I saw an engine specific thread title pop up).

Tangential question: Is it uncommon for a boat with 30A/120V service to have overcurrent protection on neutral at the on-boat 120V main breaker/disconnect?

Does the answer change if the boat has dual 30A/120V service? (In which case, there would be two breaker/disconnects)?

On the boat the main disconnect breakers should have over-current protection on both hot and neutral, but if you know breakers, a 30 amp load wont trip it off, It takes 37 amps to instantaneously trip, I tested mine once. It takes a long time to trip a little above 30 amps. And those shore plug connections are not that great, they get corroded or loose, and they can barely carry 25 amps safely due to high resistance.

So each shore cable has its own double pole breaker, on the pole on the dock, and should be one also in the boat. Lots of redundancy there.

When I rewired, I used 8 gauge wire not 10 gauge for the main wiring runs to the panel. This added a 10 amp safety factor. I thought why not, I am the one doing the work, I am not paying someone, so the extra cost was acceptable to me. I still used 30 amp double pole breakers. I also changed all onboard wiring to 20 gauge and moved the oven to 10 gauge, which probably was not worth it. But I was thinking what if all the burners and the 2 oven broilers are on at the same time, I did not want a voltage drop. So its funny that I have twin 30 amp shore power and then one of my distribution panel breakers is also 30 amps.

I also setup a double pole 30 amp switch that I can join the shore only twin 30's into one 30 on the boat, that way all circuits can be powered off one 30 amp shore cord, which is very convenient. I never run all that much AC stuff on the boat at the dock. On the water, I turn my gen on, and we might conceivably be running AC, MW, fridge and the oven all together. Interesting I just thought I could have done that with another 30 amp double pole breaker, but the switch is less space used up.

At the dock, just the AC and the fridge is running. And occasionally the MW, all 3 of those adds up to a little under 30 amps.
And the one shore cord is breaker protected to 30 amps.

 

[STB]

sdowney717,

Thanks! That's what I thought. My boat has protection on both sides, as, I think, did my last one.

I guess I saw what looked like a consensus on the thread otherwise, but I probably just misunderstood.

I think my shore power pedestal has over-current protection only on the hot side, which I guess could be problematic with a miswired boat connected to two pedestals.

Thanks again!

 

[ksanders]

Very cool[emoji847]. US or canada?

Southcentral Alaska interconnect.

Right now I’m inside, system operator of all things. Boring most of the time but with the schedule I only work about 135 days out of the year. Great way to wrap up a long career.

Previously I’ve been in a bit of everything I suppose. Hands on to engineering. Mostly substations... protection, controls, comms, that kind of thing.

Your post caught my eye when you understood parallel capacitance.

 

[diver dave]

Southcentral Alaska interconnect.

Right now I’m inside, system operator of all things. Boring most of the time but with the schedule I only work about 135 days out of the year. Great way to wrap up a long career.

Previously I’ve been in a bit of everything I suppose. Hands on to engineering. Mostly substations... protection, controls, comms, that kind of thing.

Your post caught my eye when you understood parallel capacitance.

Excellent; Keep me/us in mind if you need to measure GIC on the long transmission lines. That high latitude space weather thing!
Mostly, I do electronic designs for substation transformer and circuit breaker issues. 8 gasses in the transformer, and electrode wear on the breakers. Work in NY, but have the keys to the FL subs, currently.

 

[Rufus]

Follow up regarding the boat in question in original post. The owner did some visual investigation and says the neutral wires on both the original electrical panel and the second (added) panel are both interconnected at the single shore-off-generator switch. So he says he's going to add a second rotary switch. (As an aside, I believe there are single (long cylindrical) switches available that would accommodate two separate circuits on one control knob).

In any case I am still not clear about something...and it's relevent to the way we check other boats that use two 30 amp cords. Assuming the interconnected neutrals at the rotary switch...let's say that he only plugged in one 30 amp cord. What would we be reading with the Fluke? And let's say he then plugs in two 30 amp cords (same interconnect at the rotary switch....what would we be reading on each 30 amp cord?

Now the same questions for a boat without the interconnected neutral wires?

I ask these questions because there are many old boats with added panels....and I suspect more than a few with interconnected grounds like this guy.

A final question...are we absolutely "safe" in terms of the stray current question if we put the fluke on the fat cord of a 50 to two 30 Y splitter? Are some splitters "better" than others in this regard?

This obviously goes to issues with a very rudimentary test methodology...but it is what it is and we're trying to be as safe as possible. Further there are a huge number of cruising boats on the Lakes including looper boats that might have been "safe" in salt water...but much less "safe" in the Great Lakes. Modern sensors on the dockside system are just not in the cards in many locations.