On Thursday, 8 March 2018 16:45:03 UTC, SteveE wrote:

My 89 y/o mother can no longer reach the switch above the mirror and I
want to change it for a LED pullcord light.

The old light was installed by a bathroom fitter and was not earthed.

This light requires an earth connection but further investigation has
revealed that her upstairs lighting circuit has no earth.

Can I borrow an earth from an accessible ring-circuit in these
circumstances?

Better to take all 3 conductors from where you plan to take the earth.
Borrowing of earths does work, it's not regs compliant of course, and perhaps someone one day will disable part of the wiring system leaving the light unintentionally unearthed. By then it should be all RCDed anyway, but who knows. So don't do it.


NT