pirate repellant?

[Calvin]

I have just had a shocking experience which will repell the most determined of boarders. Grabbing the guard rail and a metal boarding ladder with the boat laid up ashore, produced a 65vAC current as measured by the multimeter. After a long search, the problem was traced to there being no earth wire connected in the box feeding the shore power to the AC boat sockets and battery charger. However, with the earthwire back on. not enough "tingle" to deter the stray boarder but still 1.2vAC as measured by the multimeter. Why have I got this discharge? Anyone with any ideas?

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[coco]

Try this: http://www.secure-marine.com/yacht/index.shtml

A lot more efficient than your 65 Volts or something!...

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[oldharry]

Two things come to mind: Firstly that the installation has got damp, so that other things are now partially 'live'. This is why earthing is so important. Second and most olikely that there were stray induction currents being generated by the main AC lines in nearby metal objects. This is a lot more common than is realised. Proper earthing shorts the stray currents. If there is still a slight voltage between the metalwork and earth, it is because the earth from the metal frame is slightly resistive, and the metalwork is still not at full earth potential. Again this is very common.

Connecting 'earth to earth' or negative to negative to see if there is any voltage potential is a standard troubleshooting technique which reveals bad connections and wiring faults The higher the voltage the worse the problem is. Any cable run will show a degree of voltage drop, and will therefore show a small voltage difference.

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[AndrewB]

A common arrangement on boats is to take the AC ground line to the boat's grounding circuit -- typically connected to the water through a metal keel or zinc, but which may well result in an electrical connection to the guard rails. This is explained in Nigel Calder's 'Boatwners Mechanical and Electrical Manual", chapter 3. I have to admit I have never grasped the logic. Whatever its benefits afloat, if a short does occur this arrangement would seem potentially lethal when the boat is ashore, specially if as in your case the shore ground was omitted.

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[malcp]

Another possibility is that many mains electronics, eg battery chargers have EMC filters in the form of low valued capacitors connected from live to earth and from neutral to earth. If the earth connection is missing or high impedance then you form a potential divider, where the earth is at half the live - neutral potential. This is something the earth connection should easily overcome unless it is of high impedance.

I suggest you carefully check your earth connections for high impedance. It might not be in your cabling but in the shore power somewhere. Measure the AC voltage between neutral and earth at the supply source and work towards your appliances on board. It should read 0 volts. I have experienced a similar problem and found the marina power source to be at fault, and not the boat at all. I am assuming you are not in the USA where the earth arrangement is different.

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