tony sayer wrote:

Now do the same with the neutral output side of the trip and it won't
trip. So why does this happen?. Remember CURRENT flow. In the first

Errr, in fact it might. There is a very good chance that a potential
difference will exist between your earth stake and the neutral connected
to the incoming side of the RCD. Hence current can flow.

instance from the live to your earthstick current is flowing from the
incoming live line, through the RCD and then via your stick and then
through the earth back to the substation where one side of the supply
the neutral is connected to earth so you can see that current flows
through the live side of the RCD back through the earth connection to
the supplying transformer. It is NOT going back through the RCD so a
current imbalance has taken place.

This is true.

The important thing is that there was an !!imbalance!! because more was
going OUT of the RCD than what was coming BACK through it!.

However when you touched the earth stick to the neutral NO CURRENT was
flowing through the live side, so no current was or could have been
flowing back!.

No, there could be current flowing back - being sourced from your earth
stake.

Now suppose you have a one bar electric fire connected to the output
terminals of the RCD. Normally what is going out is going back through
the RCD, so all is well.

Now connect that earth stick to the neutral again and it will trip.
Reason is that the CURRENT has an alternative way back to the earthed
side at the substation, some current is flowing through the RCD back to
the substation , but some is now taking the alternative route home via
the earth stick.

true...

So an imbalance is caused, their being current flowing OUT through the
RCD but it has an alternative route back and if its going back and its
NOT through the RCD so its not the same as what's coming IN, then off
will go the trip.

Simple as that.

Yup, so long as you don't fall for the BigWallop assumption that E and N
are going to be at the same potential. The only setup where that is
likely is on a PME system, and then only where there are no circuits
turned on at all.


--
Cheers,

John.

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