Possibly dangerous wiring

[Cicero]

Whilst attempting to fit a new bathroom light fitting I had a problem isolating the upstairs lighting circuit which is separate from the downstairs circuit. I traced the problem to a bridge (shown as red diagonal in picture) in the downstairs two gang switch which contains a one way (for downstairs hall light) and a two way for upstairs landing light. It required the downstairs lighting to be switched off at the CU before the upstairs two way switch (upstairs circuit already switched off at CU) lost power.

Is this an acceptable arrangement or is it just plain dangerous? Two alternative picture formats of my circuit drawing here:

a supplementary question. Is there any definitive version of wiring for a two way switch since Google appears to be littered with alternative versions?

Cic.

[Andy Burns]

IME with two-way switching of hall/landing lights, it's fairly usual for either the hall to run from the upstairs circuit, or the landing to run from the downstairs.

Probably done to save a run of cable, but has the advantage that if either lighting circuit trips you have one light from the other circuit on the floor that has tripped, similar logic to having upstairs power and downstairs lighting on one RCD and downstairs power and upstairs lighting on another.

[<me9]

Plain dangerous. It's exactly like a well known builder (with a helicopter) from the 70s left mine ( & with other faults too).

I ran a new cable to the upstairs (landing) rose from the downstairs circuit, and removed all connections to it from the upstairs circuit.

[Andy Burns]

It's only dangerous if you make assumptions, isn't it?

[Huge]

SIDE, innit? :o)

(Am I the only person in the world who has the MCB number written on every light switch and mains socket? But then, the allocation of breakers is utterly wacko in my house, since it appears to have been done in about three stages.)

[Stephen Lewis]

But... Postel's Law[1] applies just as well to domestic wiring as it does in its original context :)

Stephen

[1] 'Be conservative in what you do; be liberal in what you accept from others'

[John Rumm]

borrows a neutral from another circuit, and would hence be a no-no if you were installing today (especially with the likelihood the two circuits would be on difference RCDs).

Its not necessarily more dangerous than the "proper" way of doing it since any two way switching arrangement will result in there being a live present in a switch that you notionally think of as being on another circuit.

The preferred way is:

L ------o------------------------------------o L1 \ O--------------------------------O COM \ SL------o------------------------------------o L2 SW1 SW2

So downstairs the the hall light live and switched live are presented at the switch in the normal way and are connected to L1 and L2 on the switch. A 3&E cable then runs to the upstairs switch, connecting the L1, L2, and COM terminals on both switches together.

My preference is to wire both hall and landing lights like this, with two gang two way switches at top and bottom. That way you can switch either light from either location.

[ARWadsworth]

It is a lot more dangerous IMHO and a certain failure on an electrical inspection.

When you are working on a circuit you check that it is dead when you have turned the breaker off. With a borrowed neutral that circuit can then become live through other circuit, in this case if the landing light is switched on.

Adam

[Dave Plowman (News)]

L1 L1 0===========0 0===========0============= Line | \ / | C 0================================O C \ / \ / 0===========0 0===========0============= Switch return L2 Optional L2 Intermediate Is the most practical way.

[ARWadsworth]

Is there anyway you could run a neutral from the landing light to the downstairs lighting circuit and remove the upstairs neutral from the landing light?

The very least you can do is stick a note to the CU to warn anyone else that may work on your electrics in the future.

Adam

[John Rumm]

I quite agree that its not nice, but was more thinking about it from the point of view of approaching any two way switched light - you would be expecting the switch to have a live wire present from the "other" circuit, even with the circuit in the room switched off.

[robgraham]

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=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3DO C

=3D=3D=3D=3D=3D=3D=3D=3D0=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D Switch ret= urn

=A0 London SW

I did such a 'borrowed neutral' a lot of years back because her-in- doors decided after the event that the lights for the then new kitchen needed double switching. It was 'borrowed' off a ring main which in hindsight is even more unwise - I got caught when I replaced the CU with one containing an RCD, .. it then had to be sorted.

Rob

[Pete Verdon]

Who was the well-known 70s house builder with a helicopter?

Pete

[Bob Eager]

Barratt? with Patrick Allen?

[Cicero]

========================================= Many thanks to everybody for all the very informative replies. When I was doing my safety checking I was surprised to find the 'borrowed neutral' which appears to be such a dangerous bodge and not in keeping with the rest of the workmanship. All the wiring is very neatly laid out and clipped securely which made me think that some second person must be responsible for such a potentially dangerous arrangement, although now apparently not. It will be removed promptly.

I shall keep all diagrams safely for future reference.

Cic.

[Cicero]

========================================= Yes, there is.

This is what I had thought of doing without knowing if it's allowable as good practice. Your suggestion confirms that my plan is an orthodox solution rather than replacing one bodge with another. In fact this will actually be the easiest solution as there is good close access to everything that's needed. Many thanks for the suggestion.

Cic.

[Pete Verdon]

Oh, ok. My grandad ran a company putting up lots of cheap houses, the

70s is a believable time for him to have been doing it, and apparently he did at one point buy a helicopter[1]. I didn't think he counted as well-known though :-)

Pete

[1] Which he was so bad a pilot of that he wouldn't allow any of his family to accompany him in case he crashed. I think he scared himself one time too many and sold it on not long after getting it.

[Harry Bloomfield]

Andy Burns brought next idea :

Yes but that is not the problem...

The problem is that a neutral has been 'borrowed from another circuit. Switch the light on, isolate the supply to the other circuit and you would then assume it was safe to disconnect the neutral from the second circuit - doing such the neutral would then become live.

[Andy Burns]

I hadn't noticed that, and thought the O/P was more concerned about the link of the live from the downstairs circuit to the landing light, which I've seen in a few 70's builds.

[Andy Burns]

seriously skewed usenet propagation going on, I saw Pete's reply to your message over 2 hours ago and only just saw your message itself turn up.