2-way lighting mess

[ReverendJT]

Hello,

I have a light on a two way system which works (blows after about 4 months) but I believe the wiring is completely incorrect. The common live is taken from a different circuit to the negative which feeds the light fitting.

My question is; can I correct the wiring, without ripping down ceilings (not convinced I can after looking at the Wiki //www.diynot.com/wiki/electrics:lighting:two_way_lighting). Diagram is attached.

Any help would be appreciated.

His reverence.

Untitled

• ReverendJT
• 13 Oct 2008
• 1

 

[sparkyspike]

The wiring of the 'live' cables through the two switches looks normal to me, except for the link to L1. Is that a permanent live at the light fitting? Where does the neutral come from? What does the other switch do? What do you mean by it blowing after 4 months??

 

[ReverendJT]

sparkyspike,

The switch at the top has two light switches on it, the live (for the light which has the problem) comes from the second switch on this, a 1-way light but is on a different lighting circuit to where the negative comes from for the light pendant.

The wiring of the live would look correct but only if the negative and possitive comming into the light pendant are on the same lighting circuit, which they aren't.

The bulb will pop as you switch on one of the switches.

I hope this clarifies my picture.

Thanks

ReverendJT

 

[plugwash]

That wiring scheme shouldn't cause any functional problems though it is a violation of BS7671 and means you MUST isolate both lighting circuits before working on either of them. Ideally it should be sorted but it's not hugely urgent as long as you remember that it is there.

bulbs do often blow at switch on, if this bulb is blowing more often than would be expected then I would suspect old and dodgy switches or lampholders or lose connections.

 

[ReverendJT]

Thanks plugwash, you have put my mind at rest, it's usual state. Perhaps it is a dodgy switch/wiring. I assumed that joining two circuits would create some sort of hideous short circuit of doom. If you have the time perhaps you could explain why this isn't too much of a problem as I would like to learn.

Luckily I am fairly neurotic and always turn off all circuits of the same amps.

Thanks for the advice,

My eminence

 

[333rocky333]

If you search the words "Borrowed Neutral" on the forum, there is a few old posts, may explain it a bit.

 

[sparkyspike]

Once you have read about borrowed neutrals etc., you may still want to rewire the light. Basically this would involve removing the link between the two switches in the 2-gang (thereby removing the live feed). Then connect the live at the pendant (which is in the same sheath as the neutral you want to use) to the live at the other two way switch. You will need to alter the termnations in that switch (L - L1 - L1; SL - L2 - L2; COM - COM) and add a third core to the two cores running to your 2-gang switch for the COM connection. This is where you talk about ripping ceilings down. You will now have your light correctly wired on a new circuit. Bear in mind that you need to first identify the new circuit and check the current demand is ok. You also need to bear in mind that you will have two different circuits in one 2-gang switch. So which is worse? A borrowed neutral or two circuits in one switch?