"Andy Dingley" wrote in message
...
On 28 July, 18:24, "js.b1" wrote:

In replacing the CU, any spark should at least check...
a - There is no borrowed live/neutral condition (eg, on hall 2-way
lights). A giveaway that there is would be both Lights-UP & Lights-
DOWN on the same RCD rather than split between 2 RCD as 17th reg 314.1
would require.

This check takes 5 min.

Whilst splitting the circuits by floors might be a separate
requirement of the regs, and a shared circuit is thus a bad thing,
does this necessarily indicate a borrowed neutral? In particular,
can't a borrowed neutral exist anyway, even if the stair lighting is
supplied (live anyway) correctly? (i.e. absence of the obvious shared
circuit doesn't indicate that there isn't a borrowed neutral).

Last house of mine where I encountered this did have separate circuits
for ground and first, but the two stair lights had neutrals from two
different circuits. The middle landing's came from the ground floor
(actually the rear extension which included both kitchen & bathroom),
the upper landing's was from the first floor circuit that supplied the
bedrooms.

What's the approved method of checking for a borrowed neutral, and
proving that there isn't one?

Turning the lights on and sticking a clamp meter over the cables in the CU
is one way.

I always check the landing light before swapping a CU.

Cheers

Adam