[PSUBS-MAILIST] Earth Fault

[via Personal_Submersibles]

James,
I've found that some rubber compounds are conductive. For  instance when I 
tried to electrically insulate with a piece of inner tube from a  tyre, it 
still passed current.
Jim
 
 
In a message dated 7/27/2015 7:14:28 A.M. Central Daylight Time,  
personal_submersibles at psubs.org writes:

No.  Just sat on the trailer.

On 27 July 2015 at 11:58, Alan via  Personal_Submersibles 
<_personal_submersibles at psubs.org_ (mailto:personal_submersibles at psubs.org) > wrote:

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_ (mailto: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
>
>


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