Electricity in water / diver drownings

[hollywood8118]

So the short version of all the electric hazard is this?

1. connect to shore power, unless isolated with a isolator or better yet isolation transformer current may leak back to ground of create a galvanic corrrosion issue with the marina or surrounding boats.

2. on board sources of ac power ( ac generator or inverter ) do not pose a risk to swimmers as they ground back to them self and not the earth through water and or swimmers.

3. the great risk is only when connected to the dock, or the very rare occasion when two rafted boats shared power and a stray current connects through the grounding side of boat boats....

Is this correct???

I am so interested in this because I did get shocked from my boat during my last haul out.
I do have a isolation transformer, I was kneeling on the ground, touched a through hull, felt the tingle. Used a meter and had 117v between a screw driver stuck in the ground and the through hull. I found some moron had reversed the polarity in the boat yard outlet. Needless to say it got my attention

-- Edited by hollywood8118 on Sunday 18th of April 2010 10:03:35 AM

 

[C lectric]

Got it.*
Thanks

 

[Keith]

hollywood8118 wrote:

I am so interested in this because I did get shocked from my boat during my last haul out.
I do have a isolation transformer, I was kneeling on the ground, touched a through hull, felt the tingle. Used a meter and had 117v between a screw driver stuck in the ground and the through hull. I found some moron had reversed the polarity in the boat yard outlet. Needless to say it got my attention

-- Edited by hollywood8118 on Sunday 18th of April 2010 10:03:35 AM

This is why every boat should have a reverse polarity indicator. They're cheap and pretty easy to install. My '86 Krogen didn't have one, and the last survey recommended one.

*

 

[RickB]

hollywood8118 wrote:I do have a isolation transformer, I was kneeling on the ground, touched a through hull, felt the tingle. Used a meter and had 117v between a screw driver stuck in the ground and the through hull. I found some moron had reversed the polarity in the boat yard outlet. Needless to say it got my attention

That shouldn't have happened even if the dock outlet was wired wrong. It had to have been the result of mis wiring on the boat as well as the dock.

The "polarity" of the single phase power going into the transformer is irrelevant, so switching the "hot" and "neutral" makes no difference. If the shield of a real isolation transformer was connected to a hot or neutral, it still wouldn't make any difference, the thing just wouldn't work.

But, if your shore power socket has the safety ground connected to the hull common ground and someone wired the dock outlet so that a hot wire fed the ground wire of the shore power cable then you would get zapped just like you described.

When you install an isolation transformer, the shore power socket must be electrically insulated from the metal hull and isolated from the hull common ground. Here is a link to the manual for a Charles Marine isolation transformer that shows two ways to handle the shore power ground and transformer case grounding.

http://www.charlesindustries.com/marine_manual/93-IXFMR36N-1_PR2.pdf

Look very carefully at how the safety ground is handled. The shield in a true isolation transformer is isolated electrically and its electrical connection is brought out to the terminal strip so that it can be connected as the user desires. A normal industrial transformer may or may not have a safety shield and the case may be internally connected to the ground or neutral, effectively canceling the safety feature of a true isolation transformer.

I don't doubt for a moment that you got a tingle and measured 117 volts between the fitting and the dirt ground. What I do suspect though is that unless the conditions I described above existed, you measured a small (and very common on boats) leakage current with a high impedance digital meter. If you put a load across the fitting to earth it probably would not have indicated anything. That is where the good old fashioned analog meters are valuable for troubleshooting.

In the meantime, take a good look at how your isolation transformer is wired. Check out your shore power socket and see where the ground goes.