On Sun, 2 Jun 2019 14:42:19 +0100, John Rumm wrote:

Next door had a shower pump taken from the lighting circuit that is on a
100mA RCD; that was done by a 'qualified' electrician (domestic and
commercial).

Depending on the circumstances, that may be a sensible design decision.

The use of the 100mA RCD might be because the earthing system is TT and
hence all circuits needed to be RCD protected (even in days before this
was common) to ensure disconnection in the event of an earth fault.

It's TN-C-S - updated about 25 years ago.

If the pump is in a bathroom, there are quite possibly no other
electrical circuits available near by, and the load from a pump is only
likely to be a few hundred watts - so it will not stretch the supply.
That's the same reason other small loads in bathrooms like extractor
fans or shaver sockets are often fed from a lighting circuit.

No circuits, but the taps are on copper pipe (mine's all plastic, so no
Earth path) and the bonding's dodgey. My shower is off the 30mA RCD (same
board and basic installation, done at the same time).
Slightly worrying was that the pump was in a housing on the wall, the same
as an electric shower, and the brushes were wearing out resulting in
graphite visible around the joins and control - I don't know how conductive
that would be. Perhaps best not to have the iron bath bonded to earth in
this case.
--
Peter.
The gods will stay away
whilst religions hold sway