[PSUBS-MAILIST] Earth Fault

[Alan via Personal_Submersibles]

James were they in the water?

Sent from my iPad

> On 27/07/2015, at 10:33 pm, James Frankland via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
> Hi All
>  
> I have a very peculiar issue.  I have an earth fault on the boat. 
>  
> My test consists of holding one probe of the meter on the positive battery terminal and the other to the hull somewhere.  I was showing a reading of 24v.  So obviously a negative connection somewhere to the hull.
>  
> I went around everything taking things off and have tracked the fault down to the lights.
>  
> The lights are the trustfire ones and the negative connection is grounded to the chassis of the light.  However, when I fitted the lights, I was aware of this and so insulated the mounting bracket from the  light casing itself with a piece of rubber.  So theoretically, there is no physical connection from the case to the hull.  Only the internal wire.
>  
> Anyway, if I disconnect the lights and leave them dangling on their wires, there is no earth fault.  The lights all work, and the hull is clean of current.
>  
> So the lights must be leaking back through the connection somehow, but I cant see how.  The case is insulated from the mounting bracket with rubber and the brackets are connected to the fibreglass faring, so it shouldn't leak back?
>  
> Anyway, ive fixed it by insulating the mounting bolts with delrin washers, but I cant see how the earth could return through a piece of rubber and then glass fibre.  A mystery unless anyone can see something obvious?
> 
> Regards
> James
>  
>  
> _______________________________________________
> Personal_Submersibles mailing list
> Personal_Submersibles at psubs.org
> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles