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.

A good reason to use fuses instead of those annoying things. Or one RCD for the whole house like they used to. I will never put RCDs in my fusebox, they're a ****ing nuisance.

2) By cross wiring a circuit from two MCBs you have now made it
implicitly dangerous to maintain - since even if you isolate the circuit
you are working on, it can still be back fed from another. This is
similar to the problem you encounter with borrowed neutrals only worse.

You switch one off, you test it, find it's still live, and switch the other off. The chances of it becoming live while you're working on it are negligible.

3) If the circuits are protected with MCBs (especially if rated for
different trip currents or curves), you may end up implicitly removing
basic fault protection entirely from one or both circuits, thus creating
both fire and electrocution risks.

Pansy.

4) You may also end up removing overload protection.

However on the plus side, you would highlight that the electrical system
has been interfered with by a clueless and dangerous ****, and hence
everything should be treated with suspicion!

Or wired by someone who isn't such a pessimistic pussy as you.

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