Two Way Light Switching

[erinues]

I'm just in the process of some renovations and my current lighting has two separate circuits, one for downstairs and one for upstairs. The downstairs hallway and upstairs landing lighting switches are both dual gang two way items. The downstairs one is fed from the downstairs MCB and the upstairs from the upstairs MCB. To me this seems outrageously dangerous as to work on either of the circuits safely requires both MCBs to be switched off as they are linked together.

I don't really want to lose the facility of switching the upstairs from downstairs and vice versa and am wondering if there's a safe and legal way of doing so?

Regards

Phil

 

[bogbasher]

Why does it require both to be switched off ?

 

[erinues]

The scenario listed below can be reversed:

For the downstairs light, there is a live feed applied to the downstairs switch C terminal this is then passed to either the L1 or L2 terminals (dependent on switch position) which go to the upstairs switch. At the upstairs switch there is now power on either the L1 or L2 switch and depending on the position of the switch also on the C terminal which goes to the downstairs light fitting.

I want to work on the upstairs light switch so I turn off the upstairs lighting MCB. I unscrew the light switch from its back box and start to remove a wire from an L1/L2 terminal. I'm now suffering from severe pain or death as I removed a wire from the wrong (still live) L1/L2 terminal.

 

[bogbasher]

Being as it is a switch to link upstairs to downstairs how else could it be ?. separate switches ?
But I see your point.

 

[ColJack]

quite common..
nothing wrong with it

you always isolate all possible sources and check for dead before working on any circuit..

 

[bogbasher]

The mcbs are protection devices not isolators ?.
The mcbs arent linked either. The circuits just share the same switchbank.

 

[ban-all-sheds]

1) How often do you take the switch off and fiddle with it?

2) You now know what you have so you know how to avoid injury.

3) You also know which side of the switch is which, so you shouldn't inadvertently fiddle with the wrong circuit.

4) It's an odd way to wire it - if you rewire it with the more conventional 3C+E strappers then that would give you another way to tell which side of the switch was which.

5) If you can get a neutral from the downstairs circuit to the landing light then you can put that on the downstairs circuit and thus only have the one circuit at each switch.

 

[ColJack]

who said anything about an MCB?

I said isolate ALL possible sources. the big red switch that is double pole and removes the neutral is the isolation device you want to operate ( turn the CU off in other words. )

if you are not well informed enought to realise that there may be live wires in landing switches with a single breaker off, or that feedback from a neutral can kill you just as easily as a live wire can, then you shouldn;t be messing with electrics..

 

[Space cat]

I'm now suffering from severe pain or death as I removed a wire from the wrong (still live) L1/L2 terminal.

There are two simple ways around this problem:

1) Knowing that the double switch gets power from two different circuits, you turn them both off.

2) Knowing that you have a live terminal in there, you THINK before you remove the wrong wire then DON'T DO IT!

Personally, I would go for option one.

 

[bogbasher]

Oh they are linked.

 

[bogbasher]

mcb mentioned in original post.

 

[erinues]

Thanks for the replies, it looks like my installation is legal then. I'm an electronics systems engineer with over ten years experience in system safety management and there's no way I'd ever sign off on a system such as this. Yes these comments are true:

"2) You now know what you have so you know how to avoid injury.

3) You also know which side of the switch is which, so you shouldn't inadvertently fiddle with the wrong circuit. "

However just because I know the system layout doesn't mean the next owner of my house does. What happens when they want to change the light switch for a pretty {insert appropriate colour/metal here} and only turn off one of the circuits. Based on the current Part P regs, they would be perfectly entitled to but who's the one they're going to attempt to take legal action against? Just because it's deemed safe by a qualified person against a flawed set of guidelines doesn't mean it's actually safe.....

 

[ColJack]

1) How often do you take the switch off and fiddle with it?

once every couple of weeks when I get bored

4) It's an odd way to wire it - if you rewire it with the more conventional 3C+E strappers then that would give you another way to tell which side of the switch was which.

it's not at all an odd way to wire it, 3C+E is a fairly recent thing and before it's introduction most strappers were T+E, but then again most houses also had a single lighting circuit, so the neutral was already upstairs for it..

 

[ban-all-sheds]

It's perfectly safe if people adopt safe working practices.

If they are ignorant of how to do it safely, and proceed on the assumption that they aren't then they may get a nasty surprise, in the same way that if they are ignorant of how to cross a road safely, but proceed on the assumption that they aren't.

 

[bernardgreen]

The other safety aspect is the situation when a lighting MCB is tripped off for any reason.

The way you have it now you can lose one lighting circuit and still have some lights on the stairs.

However just because I know the system layout doesn't mean the next owner of my house does. What happens when they want to change the light switch for a pretty {insert appropriate colour/metal here} and only turn off one of the circuits

Prepare some hand over notes for the next owner and fix a second copy firmly next to the consumer unit.