is this wiring correct?

[AJH]

I posted a similar message last Friday but it never appeared, if it does apologies!

My electrician wired up the new extension some weeks ago. I tried to replace a light switch in one of the bedrooms with a dimmer. The prob is that he seems to have brought the live feed for all the upstairs lights up through the switch back box. The neutrals are joined with a 'choc' connector inside the box, the feed from below goes to com 1 and then looped to com 2 from where it carries on up to the loft. the bed lights are fed from L1 terminal. The dimmer has just 3 terminals L1 L2 and one with a sine wave which I assume is live. This means I need to connect all 3 lives into one terminal and to be honest it's not that big. Does it sound like normal practice to take the onward feed to other lights via the rear of a dimmer??

[Palindrome]

So why not put in a second insulated choc block and use it to join the lives?

It sounds like the existing switch is a two gang switch. Are you trying to replace this with one dimmer?

As for the dimmer, it should have come with wiring instructions. Follow those. Never make assumptions about electrical wiring - if you haven't got instructions, trace the wiring to and from the triac. If you aren't able to determine what its wiring is, get another dimmer switch *with* instructions, or get an electrician to do the work.

It would help if you could describe what *cables* terminate in the box and how their *cores* are connected. eg, something like:

Cable 1 : Incoming Supply.

L to common 1 of first switch gang, looped to common 1 of second switch gang.

N to neutral choc block

Cable 2: Onwards Supply

L to common 1 of second switch gang.

N to neutral choc block

Cable 3: First Light circuit

L to L1 of first switch gang

N to neutral choc block

Cable 4: Second Light circuit

L to L1 of second switch gang

N to neutral choc block.

[AJH]

You have worked it out correctly there is a 2 gang switch there already but no cable for the 2nd circuit. I am replacing with the dimmer. I know you should follow exactly the existing connections but there are only 3 terminals available. I understand what you say about joining the lives, and thanks I will try that. I just wondered if joining in the back box is acceptable practice as I need to get it certificated for Building Control. I suppose I am a bit suspicious as my electrician forgot to put a 3 core interlink cable between the smoke alarms. He put in 2 core T&E supply to each from the board. When I queried this he said 'oh no problem I'll just link them at the board'. When I checked with the alarm manufacturer they said if he does that he'll fry the alarms. I am now in the throes of routing the missing cable from the upstairs landing alarm to the downstairs one. It would have been a lot easier if he had done it right to begin with. I am also suspicious as since I mentioned the need for a cert. and the 3 core problem he has just not ben in contact even though he is owed money on the job.

[Palindrome]

If done properly, no problem.

I thought that the link was L + N + Alarm.

Why have each got a supply from the "board"?

Why would linking the two cores (L + N) at the board "fry the alarms"? They are linked by the board, in any case..

I suspect that you will have to disconnect the existing cable in all but one of the alarms and leave it isolated and with ends suitably insulated.

[AJH]

echie at AICO said.

I was going to leave the T&E supply to one alarm then run a 3core interlink cable to the other one, this is what it says in the instruction booklet.

[Palindrome]

That sounds good to me. However, I still have no idea what the company was on about, saying that commoning up the T&E cables at the panel would "fry" anything.. IMHO, All that would happen is that the alarms would operate independently.