Very Strange Electrical Hazard/Problem

[Maine Sail]

Yep! This is a weird one. I was standing in grass. b
It would have to be AC then.... but I am stumped on how the current is getting to my engine mount in the first place.

The only electric lines I have going aft are the rear nav. light and the starter cables to the outboard. I've disconected the starter cables and the nav. light line is not touching the transom as far as I can see.... and I don't think the transom has any metal in it..... so who would I get capacitive current....

I'll post something as soon as I figure it out.

r

Many "cheap" non marine UL chargers can put AC power on DC leads if the plug gets reversed or there is an internal leak of failure. This is why automotive type chargers should not be used on boats. Remember your AC ground (green wire) and DC ground will or should be tied together on-board the boat, but AC neutral should NOT be tied to AC & DC ground on the boat.

*Unplug charger - Check for tingle

*Unplug boat test for continuity between AC NEUTRAL & AC GREEN. Should be NO continuity here.

*Now check for continuity between AC GROUNDING/GREEN & SHIPS DC GROUND/BATT NEG. There SHOULD BE continuity here.

*Check all connections and ensure BLACK, WHITE & GREEN AC all go to the correct terminals

*You should have a double pole AC main breaker that interrupts both hot and neutral but never AC GREEN.

 

[walt]

So.. when you touched the outboard, you were at earth potential, the outboard and the water bucket were at the same potential - but connected to what.. we dont know. However since you got a tingle, the outboard was not a earth potential because you were and you got a shock.

I just did a little experiement. I put an alumimun ladder on the grass (see the attached picture) so that the ladder was at earth potential. I wanted to see if the green wire on the extension cord coming from the house was also at earth potential. It was - I measured very close to zero AC between the ladder (or the probe stuck directly in the earth) and the green wire on the extension cord.

However... I discovered that the plug that this cord comes from has the hot and nuetral switched Sort of "funny" since its been this way for since I bought the house over 20 years ago..

 

[walt]

Since you asked about capacitance (since its a mistery how the outboard might be gettiiing charged)

I don’t think capacitive coupling is causing your issue.. but here is how it works..

http://en.wikipedia.org/wiki/Capacitance

To get capacitance, you need two conductors separated with an insulator by some distance. The insulator between the conductors matters because the insulator has a parameter called dielectric constant and it affects the capacitance.

The equation C = dielectric constant* another constant * area of the plates / distance between the plates.

The dielectric constant here is either air or fiberglass which are not that far apart (air is 1, glass is probably about 2).

So to increase capacitance (which results in more AC current), you either need to increase the area of the plates - or decrease the distance.

An example, say you put on rubber boots on your feet and were standing on the ground. The area of the plate would be the area of your foot print on the ground. In this case, the distance between the plates might be the thickness of the rubber - i.e., very small. Since capacitance is 1/distance, you might actually have fairly high capacitance in this case. Increase the thickness of the rubber and the capacitance would fall off quickly (1/d).

Also, current in a capacitor is related to how fast the voltage is changing. Faster change - more current. 60 Hz is slow – very little current for the very small capacitance likely on the boat.

 

[LloydB]

Put everything back together the way it was when first shocked. (don't touch the motor) Measure the ac voltage between the earth (ground you were standing on) and the motor. Start with a high voltage range then switch to lower until you get a reading. Use a big screwdriver pushed into the dirt for a good connection the meter probe doesn't have enough surface area to give a fair reading. If you don't get a reading switch to dc volts use same procedure. Report back, we might get to page 4.
FYI dry skin doesn't conduct current as well as wet skin first layer skin as well as second

 

[Bill Roosa]

Your boat is insulated from a true earth by the trailer tires. When you plug into shore power it is "grounded" by the ground wire. ANYTHING that leaks to ground from the AC system should be grounded out by the shore power ground. I'm thinking the battery charger but any AC appliance could be the cause. Should be able to find it by switching devices in and out of service and seeing which is causing the problem.
Another possibility is that the ground plug on the shore power cable (both ends) is not making a really good (couple 10s of volts??) connection and you are completing the ground between 0 true and 20ish boat grounds. This would only happen when current is flowing in the shore power cord however.

 

[rgranger]

I made some progress

Thanks Main and Walt and everyone else...

Main: I do have a marine rated battery charger... but I think you may have hit on something with the ground wires.

I stuck the black lead from my voltmeter into the ground and touched the outboard cowl with the red. I got 50V AC. I also got 50V AC off of the swim ladder so ... it would seem the entire boat is energized somehow.

I disconnected the battery charger from the AC line and the voltage off of the boat to ground dropped to 10V.

I manually tripped the GF outlet and the voltage dropped to 1V AC.

I pulled the junction box cover off of the back of the 2-pole circuit breaker and discovered that the ground coming from the shore plug was connected to ....nothing. It was just floating free.

I stopped at Walmart and picked up an Atwood battery charger. It is not as substantial as the one I had but I'm only running a few fans and a VHF so I don't burn that much juice. I'll swing by Lowes and get a new GF outlet and I'll connect the grounds properly.

Then we will see what is up ...

 

[walt]

discovered that the ground coming from the shore plug was connected to ....nothing. It was just floating free.

Just for the data point, I wonder if you could fix only the green ground before you do any other fix's and see if the outboard voltage goes away.

 

[LloydB]

Before you get too far along you should check to see if there is voltage between safety ground and neutral and if each reads the same voltage to hot in the power cable. Check also for a difference between the cable grounds and the earth as you could have both a ground fault in the supply and a ground wiring fault in the boat.

 

[rgranger]

Fixed!

Hey All:

You all were great. I got my electric "leak" fixed. It was a grounding issue. The ground wire on the line coming from the shore connector to the circuit breaker was not connected to anything. Before I started fixing the grounds I was reading 80V AC and 12V DC between the shrouds and a lead stuck in the ground. A few other grounds (including the one to the battery charger) were also not connected. I went through each component and got the grounds all connected and my voltage leak dropped to 0.01V AC and 0.00V DC.

I still don't really understand how so much electricity could be traveling through fiberglass but... now it is gone so I feel a lot better.

 

[Allan12210]

Hey All:

You all were great. I got my electric "leak" fixed. It was a grounding issue. The ground wire on the line coming from the shore connector to the circuit breaker was not connected to anything. Before I started fixing the grounds I was reading 80V AC and 12V DC between the shrouds and a lead stuck in the ground. A few other grounds (including the one to the battery charger) were also not connected. I went through each component and got the grounds all connected and my voltage leak dropped to 0.01V AC and 0.00V DC.

I still don't really understand how so much electricity could be traveling through fiberglass but... now it is gone so I feel a lot better.

Excellent work. I had to do a search to see your posting as I missed it first time around and was wondering what happened. Appreciate you sharing..its been a learning experience. I don't know why there was current flowing either unless there was some conductive material in the fiberglass (a layer of carbon fiber for extra strength?). Maybe it was a surface effect due to an oxidized layer that is marginally conductive. Have to test the surface with a four point probe and determine the resistivity (a material property) I guess.

 

[walt]

You can explain the AC going to the boat grounding since the green wire in the power cord must have been connected to something on the boat. The power cord would have a long run of the hot wire right next to green wire and it would have picked up the AC through capacitive coupling. Also means the situation was never really dangerous.

The rest.. very odd. I agree with Alan12210. If you can not find any physical wires between all the stuff that had AC on it such as the outboard, the only explanation is that somehow the fiberglass is in fact conductive.

Youre probably tired of messing with that now but I wonder if you took an ohm meter and measured the resistance between green AC ground on the boat and for example the outboard (with everything on the outboard disconnected like you had at one time and also the "shore power" cord completely removed so the boat is completely isolated), would you see some resistance. It might be a high value like 100K to 1Meg, maybe even higher although at higher Im not sure if you would have felt a tingle). I dont think you can explain that any other way..

 

[rgranger]

.... Maybe it was a surface effect due to an oxidized layer that is marginally conductive. Have to test the surface with a four point probe and determine the resistivity (a material property) I guess.

Allen is that a polite way of saying mildew and mold might be conductive...

 

[rgranger]

You can explain the AC going to the boat grounding since the green wire in the power cord must have been connected to something on the boat. The power cord would have a long run of the hot wire right next to green wire and it would have picked up the AC through capacitive coupling. Also means the situation was never really dangerous.

The rest.. very odd. I agree with Alan12210. If you can not find any physical wires between all the stuff that had AC on it such as the outboard, the only explanation is that somehow the fiberglass is in fact conductive.

Youre probably tired of messing with that now but I wonder if you took an ohm meter and measured the resistance between green AC ground on the boat and for example the outboard (with everything on the outboard disconnected like you had at one time and also the "shore power" cord completely removed so the boat is completely isolated), would you see some resistance. It might be a high value like 100K to 1Meg, maybe even higher although at higher Im not sure if you would have felt a tingle). I dont think you can explain that any other way..

Thanks again Walt

What you are saying makes sense.... but I didn't see anything obvious. The only ground wires that I found .... were connected to the AC outlets. These were just standard outlets from a hardware store and the ground wire was attached to the green screw on the outlets. BUT! There are so many orphaned wires on this boat, it is possible that there is an energized line someplace that is just laying against the hull. After I return from this trip, my next project is to isolate all of the electric lines that I actually use and tear out all of the orphaned lines... clean things up and label everything.

One thing I'm fairly certain of....it definitely had something to do with the battery charger not being connected to ground. I still had AC leak before I fixed that.

 

[Davidasailor26]

My guess is that the root cause is still present, just masked by the fact that the ground is now connected so the current has a better path to take than through you.

 

[walt]

I was still somewhat curious about how resistive fiberglass is so did a little experiment on the glass boat that I have handy. It’s an old C15, I can’t remember the year but it’s in the 30 to 40 year old range.

What I did is to find two metal parts on the boat that had multiple screws directly into the fiberglass.

I then drove one of the metal pieces with the black hot wire from 110 VAC. I used a DVM with the ground lead to the earth ground of the AC source and measured the voltage on the second metal piece that was 3 inches away.

Attached are the two pictures and you can see that the piece of metal I was driving had 123 VAC on it. When I measured the second piece of metal that was three inches away and electrically isolated except by the fiberglass, I measured 3.5 VAC.

This is a fairly good meter (but been around for a while) and if I assume that it has an input impedance of 20 Meg ohms, I can calculate the resistance of the fiberglass (simple voltage divider, ohms law).

In this case, the resistance between those two metal structures calculates to be 680 Meg ohms (680 million ohms).

I can then calculate the current that was flowing in this case with 120 VAC = 0.18 uA (.18 millions of an amp - basically almost nothing).

If I had touched the second piece of metal that had the 3.5 volts on it, I might have felt a small tingle but it would not have been dangerous at all.

Also, I measured another piece of metal (stay attachment) about five feet back from the drive and basically got zero AC.

So.. on at least this C15, I would say the fiberglass is a tiny- tiny bit conductive but really almost nothing. For all practical purposes, it is a fairly good insulator. If you look close enough, even air at low voltage is slightly conductive..

 

[SeaTR]

So, help me out here you electrical gurus, would this be refered to as a "floating ground" problem that rgranger had ??

 

[rgranger]

Thanks Walt.