Sparks wrote:
I tried disconnecting it's earth (and keeping away from it!), and the
tripping stopped
If I measure the current from it's earth wire to earth, the RCD trips
(no surprise there then!)
If I measure the current between its earth wire and Neutral, I am
getting about 2.9A
If I measure the voltage, it is about 120v
There've been quite a few replies explaining that this measurement isn't
valid, or at least is irrelevant to the problem, but I am note entirely
clear on why. My understanding of the test that you are performing is as
follows:
Appliance L connected to Supply L
Appliance N conencted to Supply N
Appliance E - not connected
Supply E - not connected
You then place the multimeter from the appliance earth to supply neutral,
and it read 2.9A. To me, this clearly doesn't sound healthy. In a healthy
appliance, the earth should isolated from both live and neutral (with the
exception of a high impedance link via the noise suppression caps), and
should hence not be able to supply any current to neutral.
The point that was being made is that if you place a multimeter between the
supply earth and neutral then significant current will flow. This is
clearly true, as N and E are held different potentials via a relatively low
impedance, depending on the earthing system. However, in Sparks' case, he
is not measuring current from supply earth to neutral, but from the
appliance earth to neutral, and the appliance earth should be isolated from
any potentials as he has disconnected the earth terminal. It is possible
that some form of supplementary bonding is in place, and introducing a
potential on the appliance earth, but this seems unlikely because his RCD
ceased to trip when the earth terminal was disonnected. Also, the fact that
the RCD doesn't trip, even when the multimeter is showing 2.9A flowing to
neutral, suggests that this current is being sourced from the RCD protected
supply.
If my understanding of the tests that have been performed is correct, then
this does sound clearly like a faulty device.
Chris Key
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