[PSUBS-MAILIST] Earth Fault

[Sean T. Stevenson via Personal_Submersibles]

What sort of cable? Is it possible that the power supply common is being connected to chassis ground through the cable shield?

Sean


On July 27, 2015 4:33:32 AM MDT, 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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>
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