John Rumm wrote:
wrote:
The small link is for the live and is called a bus bar. It is three
lugs that slot into the live terminals of all three switches of RCD and
two mcbs.
Yes, and the Neutral bus bar will be elsewhere in the CU and fed via a
link cable or rod from the other terminal on the *bottom* of the RCD.
Well, no. From the description given above the incoming supply must go
to the top RCD terminals because the bottom ones would appear to be the
outgoing feeds to the 'live' (strictly, phase) busbar and to the neutral
bar.
Yes, that appears logical. Live in top of RCD and lives out to mcbs via
a small bus bar. It is the neutral wire from the neutral terminal that
goes directly to the output terminal of the RCD, which has thrown me.
The Neutral of the supply is connected to the *top* of the RCD - next to
the Phase from the supply. The outputs from the RCD are at the bottom,
one to the phase bus bar (metal thing with lugs), the other (typically
[1]) via a cable to a neutral bus bar - multiway cable terminal with
screw downs.
[1] some small CUs with only a few ways actually mount the neutral bus
bar directly into the output terminal at the base of the RCD or main
switch.
The neutral is not switched through the RCD, although a terminal is
there to switch it on the RCD. I assess that this is to make the RCD
work not being familiar of operation.
No - the neutral *is* switched via the RCD. Both phase and netural must
pass out and return via the RCD in order for it to operate correctly.
The two outgoing final circuits are taken from the top terminal of each
MCB and the neutral bar.
Thanks. I get it now. The CU has two terminal strips, earth and
neutral. The live and neutral come in and connect to the "top" of the
RCD switch. The earth goes straight to the earth terminal. The output
of the RCD switch has the live going to the two mcbs via a amll bus bar
link, the neutral to the neutral terminal strip. When the RCD is off
there is no supply to the live bus bar or neutral terminal strip,
cutting out the lives and neutrals to all circuits. This makes sense.
The mcbs have the live from the output of the mcb and take take the
neutral from the common neutral terminal trip.