Yep, this is exactly what I did Disconnected the earth from the
connection plate, then clipped one test lead to it, and the other the
Neutral in the connection plate (as connecting it to the earth in the
plate trips the RCD)
I also tried clipping the test lead to the metal body of the hob and the
neutral in the connection plate - both displayed the same results of 2.9A
flowing (The test lead produces small sparks when connected too)

Whoa - not the way to go. Remember that when you have your meter set to
read current it looks like a short circuit across its probes (because it
is meant to be placed in series with a circuit - not across it like when
measuring voltage).

Yea, I know! I wanted to see the current flowing out of the earth

If I understand what you have written correctly then
you have just created an earth neutral short

Nope, if I plasced the test leads on the earthe on the supply earth and
supply ~Nuteral I would have done this

.. A sure recipe for tripping
a RCD in many cases. What sort of earthing do you have?

TN-S

What you need to do is leave the live connected to the live, neutral to
the neutral, and then disconnect the earth. Now connect one test lead to
the earth connector on the appliance, and the other one to the earth wire
you just disconnected.

That will trip the RCD, as the leakage is a lot more then 30mA

That will let you measure the current
flowing to earth.

As this method trips the RCD, I connected the probe the the Nuteral, as it
is at the same potential as earth

You will probably need you meter on a lower range! You
may still get a trip when you do this - but you should be able to get a
reading for the leakage current.

It trips as soon as the meter touches the copper, so I cant get a reading
quick enough!

You could try turning off other RCD
protected circuits at the CU for the duration of the test to desensitise
the RCD (by removing other sources of imbalance/leakage) if required.

Not really applicabalw with my test - it is definatly dumping 2.9A to earth!

Sparks (who wants to RCD everything possible, now more than ever!)

Why?


Because if the hob is faulty, as I expect it is, this fault would not
have been identified as the leakage would not trip the 32A MCB - Say at
some point the earth gets disconnected for whatever reason - the chassis
of this hob will be ready to supply a user with 2.9A @ 120v - and as it
is only leaking 2.9A no protection device would trip.

If it is faulty, then passing 2.9A to earth would be a rather odd fault. I
expect you are simply measuring a large current flow between N and E

Well, sort of - the disconnected earth of the hob and the N of the supply.

as a result of a slight difference between your earth and neutral
potentials. You would also not have been able to use the cooker to boil
your pan of water unless your RCD was also seriously knackered as well
since 2.9A should trip a 30mA threshold device rather rapidly.

I havent managed to measure the current when the RCD was staying on - so
mabe when this was happening it wasnt leaking quite so much!
The RCD is only about a year old - it was replaced as the pervious one went
well over sensertive

(I take it it trips when you hit the test button?)

Yep, and also when it was tested recently with an RCD tester )