Mike Clarke wrote:
John Rumm wrote:

What any of this has got to do with 12V wiring and plugs though I can't
quite see at the moment.

From the OP's second post I think they discard the live pin and use the
neutral and earth pins when using the sockets in a 12V circuit. So in
theory it should be safe if a 12V appliance is plugged into a mains socket
since N and E should be at the same potential. But in practice it just
needs an error like reversed L and N on a mains socket for plugging a 12V
appliance into it to become very serious.


Daves description / explanation of the problem seems somewhat
inaccurate, but yes there are rare situations in whcih the mains earth
can become live. However on anything other than a historic
installation, mains power would be cut off immediately at the CU /
fusebox / distribution board. And if everything in the house becomes
live for a moment, the potential addition of a 12v appliance to that
event is insignificant.

FYI there is more than one earthing system in use in UK, and the
scenario works out differently dependant on the system in use. The
nasty possibility is a 1950s install with local earth rod and no RCD
or ELCB; these can stay live indefinitely.

The other problem is as Mike says, one trivial mistake on a mains
socket or jbox and your 12v appliance can have live mains on it.
Checking all wall sockets doesnt prevent this, as extension leads can
also be miswired.

What could work is modding the plugs & sockets. Add a pin to the 12v
plugs (eg a small bolt) and drill a hole in the 12v sockets, and the
12v appliances cant plug into mains any more. However, easier just to
buy suitable plugs.


NT