[PSUBS-MAILIST] Earth Fault

[via Personal_Submersibles]

Marc,
That was a little more than 50 years ago I tried to use a  piece of inner 
tube to insulate an attachment on an electric  stock fence.  Didn't work, but 
I learned something very quickly.   Rubber boots insulated you pretty well. 
 If you wanted to check operation  of the fence, you could grab the fence 
with one hand and touch the other hand to  the ground.  You knew right away.
Jim
 
 
In a message dated 7/27/2015 9:11:01 A.M. Central Daylight Time,  
personal_submersibles at psubs.org writes:

Lots of  carbon black in tire rubber.

Marc

On 7/27/2015 8:28 PM, via  Personal_Submersibles wrote:
> 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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