electric shocks

[rhinojohn]

Hi wonder if anyone out there can advise, about the end of the first week of a two week holiday we start to have probs with people picking up little shocks that are like the static ones you get from car doors and shopping trollies, we get them from the seat backrest the remote controls for forward reverse and tilt n trim and when we are knelt on the deck reching over and washing fish in the sea, also the engine runs on after being turned off with the key and then the killcord being pulled, have checked wiring under deck and all are in good condition. The engine is a 1993 MERCURY 60HP 2 stroke than runs well otherwise.
So over to you guys, thanks.

[Trailer Bloke]

witch craft

[biffer]

Bad earth somewhere

[rhinojohn]

As to witch craft, trailer, its a rimimi and To Biffer any clues as to wgere i should look, thanks

[EnglishLes]

Originally Posted by rhinojohn

As to witch craft, trailer, its a rimimi

The "And a Pickpocket" prize for not getting the joke goes to ......

[kerny]

:d:d:d

[kerny]

[willk]

Originally Posted by EnglishLes

The "And a Pickpocket" prize for not getting the joke goes to ......

Maybe you, Les

I think rhinojohn knocked that serve from Trailer out of the court deliberately, certainly I had a larf...

[rhinojohn]

Spot on Willk and the prize actually goes to Les.

[EnglishLes]

Originally Posted by rhinojohn

Spot on Willk and the prize actually goes to Les.

I'd like to thank my mother, the director, the best boy,the worst girl, all the contributors to the Forums who either can't spell/type without which/witch I would never have won this award!

[rhinojohn]

Ok all joking aside now, any chance of some ideas on what the problem might be and what to check on. Bad earth seems likely but what to look at ?

[biffer]

Like I said 10 posts ago. Trouble is it could be anywhere. I had a same problem on a boat and found they had used one single wires on the nav lights and earth the a frame. When everything got damp you are the better earth.
Could be anywhere. Start in the controller

[EnglishLes]

To get a shock the voltage would have to be quite high therefore not the normal electrics (12/24V).

It could be static or something on the high voltage side of the engine.

The running on (assuming it's a keyed ignition) would indicate that there is still some flow of current. This could be induced from another circuit.

Some things you might try are:

do the problems occur if only the engine has been started without the boat being driven,
after driving do you get more than one shock by doing the same thing,
is it related to any particular instruments.

[Cookee]

Originally Posted by EnglishLes

To get a shock the voltage would have to be quite high therefore not the normal electrics (12/24V).

For what it's worth I agree with Biffer on this one - it doesn't have to be more than 12 volts!

[Pikey Dave]

If you're wet, 12v gives quite a tingle.

[Erin]

It is the current flow that gives the shock/tingle, not the voltage. The PD (that's potential difference not PikeyDave) required to give said shock depends on the resistance of the path to earth. Obviously if you are wet and holding on to a 'live' A-frame with one hand whilst the other is in the briny then your resistance to earth is going to be much lower than if you were dry and not touching the sea. Normally you require a high voltage to get a shock as the resistance is too high for a meaningful current to flow. Bear in mind 9v is enough to give a tingle as anyone who has tested a PP3 battery on their tongue will attest . Over 30mA is deemed dangerous hence why household RCD's usually trip at 30mA. The old party trick of static electricity in a balloon which makes your hair stand up is many thousands of volts, but there is insufficient 'charge' and therefore current available to electrocute you (otherwise there'd be a lot of demised kids entertainers and children!).

Also, if there is any coil or transformer that is causing the stray current then the shock is greater if it is switching. The induced reverse voltage as a coil is switched off is very high, hence why coils are used for ignition. It could be an ignition fault due to moisture in the engine or a damaged HT lead giving this stray current.

[Turbodiesel]

On that engine check that the earth strap from the powerhead to the lower cowl is ok if not it will earth through you. Look at item 27 on the parts diagram it should be around that area.

[rhinojohn]

Thanks everyone, will be looking at it tomorrow now

[willk]

Originally Posted by Erin

Obviously if you are wet and holding on to a 'live' A-frame with one hand whilst the other is in the briny then your resistance to earth is going to be much lower than if you were dry and not touching the sea.

And there it is: Resistance. If you're wet and salty, you can get a tingle off almost anything (reminds me of my old college days )

[willk]

Originally Posted by Erin

Bear in mind 9v is enough to give a tingle as anyone who has tested a PP3 battery on their tongue will attest

You were at the wrong parties