On Sat, 12 Sep 2015 19:04:25 +0100, John Rumm wrote:

On 12/09/2015 17:16, Tough Guy no. 1265 wrote:
On Sat, 12 Sep 2015 17:11:19 +0100, ARW
wrote:

"Tough Guy no. 1265" wrote in message
news On Sat, 12 Sep 2015 16:54:51 +0100, John Rumm
wrote:

A different circuit wouldn't matter. Same voltage, same phase, etc.

A different circuit *would* matter. Think about it.

I have, and there is no reason. The voltage and phase from it is
identical.

Try again, voltage or phase are not the issues.

I won't try again, because there is no other reason.

Dennis and John have both given different reasons.

Both are viable reasons.

Nobody gave any reason, all I've seen is "It would matter".

OK, subtitles for the hard of thinking:

1) If you combine the switched live connections of two circuits powered
via different RCDs, then you will get a RCD trip on one or both devices
the moment the light comes on.

The trouble with RCDs is they aren't intelligent. And they stop you taking nice shortcuts like using an earth as a neutral. Or grabbing a neutral that happens to be nearby on another circuit when you're in a cramped space in the attic and can't be bothered finding the right one.

--
What lives in the sea, and goes dah di dah dit, dah dah dit dah?
A morse cod.