Two circuits, one accessory?

[Donkmeister]

In my house (wired in 1998 by an electrician), there is a 2g switch at the bottom of the stairs that controls the light at the top of the stairs (two-way switching), and a light in the hallway (ground floor).

I've just checked and if I isolate the downstairs lighting circuit, the hallway light is dead but the upstairs light can still be controlled... The upstairs light is on the upstairs lighting circuit.

I thought it was against regs to have such an arrangement without a big warning sticker on the front, something along the lines of "this enclosure contains multiple circuits" Or is there some reason that this would be allowed, bad design practice reasons aside?

The reason I ask is that in my rewire it would be useful to continue such an arrangement whilst leaving the upstairs light on the upstairs circuit. The alternatives are to place upstairs light on downstairs circuit (seems sloppy) or have two separate 1g switches in the hall (looks untidy).

Looking in my 17th Edition I would say that 514.11 and 537.2.1.3 forbid this without a suitably placed warning. Without these two regs though, 514.10.1 would accomodate it because nominal voltage doesn't exceed 230V.

 

[Taylortwocities]

I think you know the answer. The switch and the consumer unit should have suitable notices to indicate that the switch is fed from two different sources.

What you describe is very common in many houses and i have yet to see a notice properly posted to warn of the hazard (except ones that I have installed, of course!)

 

[flameport]

514.11.1 refers to items 'which are not capable of being isolated by a single device'. In a house, the main switch will isolate both, and this is the single device required.

537.2.3 regarding the notice is primarily about 2 separate supplies, such as would be found where a generator and mains supply could be present, or for PV systems. In those cases, it would be necessary to isolate both the mains supply and the generator as separate items to ensure all power was disconnected.
That won't apply in a house.

Additionally, there is no requirement to have lighting split upstairs/downstairs, it could just as easilt be split left/right or 1 circuit per room, or not split into multiple circuits at all.

 

[Taylortwocities]

I take your point, up to a point. I wonder why MK provide their grid systems with just such a label.
Maybe they expect there to be multiple supplies used in the average installation.

I shall continue to post warning notices/

 

[flameport]

BS7671 is only the minimum standard, nothing wrong with providing additional warnings.

 

[Donkmeister]

Additionally, there is no requirement to have lighting split upstairs/downstairs, it could just as easilt be split left/right or 1 circuit per room, or not split into multiple circuits at all.

Oh, sure. My old place was a lot smaller so only had one lighting circuit.

I was thinking about the situation where someone flips the MCB for "Downstairs lighting", flips the switch a few times, takes the faceplate off and then only checks one of the browns for live.

That would be down to their carelessness, but as I'll have to get it signed off by BCO I thought I should check it can be done before I do something that needs to be redone

So does that mean it is OK to switch two lights on two circuits inside a 2g switch? Obviously using one gang for each!

 

[electronicsuk]

So does that mean it is OK to switch two lights on two circuits inside a 2g switch? Obviously using one gang for each!

Yes, that's fine. You can't win either way, as the alternative would be for the landing light to be fed off the downstairs lighting circuit. This would kill the supply to both switches at the bottom of the stairs when the downstairs supply is isolated, but conversely, someone working on the switch at the top of the landing (or the light fitting itself) might assume it to be fed from the upstairs lighting circuit, which wouldn't be the case. It may, however, allow you to avoid multiple circuits in a single accessory if the upstairs switch controls only the landing light.

 

[Taylortwocities]

So does that mean it is OK to switch two lights on two circuits inside a 2g switch? Obviously using one gang for each!

It is BUT be sure to keep the lives and neutrals separate when you do your wiring. Otherwise you will create a borrowed neutral situation and your RCD will trip.

 

[ban-all-sheds]

The reason I ask is that in my rewire it would be useful to continue such an arrangement whilst leaving the upstairs light on the upstairs circuit. The alternatives are to place upstairs light on downstairs circuit (seems sloppy).

It's far from sloppy - it means that if you lose the upstairs light circuit you still have light available over the stairs. If you lose the downstairs one you still have light available from the rest of the rooms on that floor.