On 21/10/2017 20:14, Yam man wrote:
replying to John Rumm, Yam man wrote:
Pics of cu fuse and meter if it helps.the rcd used as main switch on far
right
is only 1 that is tripping off. https://www.homeownershub.com/img/bd
https://www.homeownershub.com/img/be
https://www.homeownershub.com/img/bf

Ah, good. Thanks for that.

That looks like you have got a classic 16th edition "split load" style
TT install since I can't see any earth connection from the main cutout.
(quite neatly wired in the CU as well)

http://wiki.diyfaq.org.uk/index.php/TT_Earthing

The RCD in question is a type "S" which means it also includes a time
delay - this allows discrimination with the 30mA trip RCD you have on
the left hand bank of circuits. (i.e. if there is a earth fault that
causes 150mA of leakage on one of the left hand circuits, the delay
gives chance for the 30mA device to clear the fault first without
tripping the upstream RCD)

So given that, you *can't* just bridge out the RCD since there is no
guarantee that your earth impedance is low enough to clear a fault on
the right hand side bank of circuits without it.

If you are still getting a trip with all the MCBs off (and other RCD),
then its still likely to be a faulty RCD.

There is one other possible cause, and that would be if you have N to E
short circuit - probably on the lighting circuit you have been
extending. If this fault is combined with a slight voltage rise on the
neutral of your supply (which can be caused either by your own load on
it, or a neighbours), then you can get a trip because a little bit of
current flows through the neutral of the RCD to earth, and that is not
balanced by equal current in the live.

You could test for this by measuring the resistance between your
rightmost neutral bus bar, and the earth bus bar (with everything turned
off obviously). If you get a low resistance, then disconnect the neutral
wire into terminal 2 on the right most neutral bar, and measure the
resistance to earth from that in isolation (i.e. testing just the
circuit you know you have been working on).

(Note I am assuming its been wired with the neutrals into the numbered
position matching that of the corresponding MCB!).

If you wanted to test the main RCD just on its own, again everything
switched off. Disconnect the two thick wires into the two right hand
terminals of the right hand neutral bus bar, tape the ends just so they
are not flapping about, and turn the main switch on again. If it trips
then it must be faulty.


A suitable replacement would be something like:

https://www.tlc-direct.co.uk/Product...100slash2.html

(note however replacing that would mean pulling the main switch in order
to work safely since you have no other way of turning off those live
meter tails coming into the top of it)

--
Cheers,

John.

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