[PSUBS-MAILIST] Earth Fault

[hank pronk via Personal_Submersibles]

James,
I have had this problem with rubber washers.  Some rubber contains carbon, I always put an ohm meter on material that needs to be an insulator.  Your rubber is likely a conductor.
Hank--------------------------------------------
On Mon, 7/27/15, James Frankland via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Subject: Re: [PSUBS-MAILIST] Earth Fault
 To: "Personal Submersibles General Discussion" <personal_submersibles at psubs.org>
 Received: Monday, July 27, 2015, 6:13 AM
 
 No.  Just
 sat on the trailer.
 On 27 July 2015 at 11:58,
 Alan via Personal_Submersibles <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>
 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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