Lighting Problem

[John]

This morning our dining room lights (one central fitting) didn't come on, they worked last night. I have done some investigating as far as my electrical knowledge is concerned.

1. The MCB hasn't tripped, all other downstairs lights work, I know the dining room light is on the same MCB as I replaced the light fitting about 6 years ago.
2. The fitting is OK, (I have for the investigation swapped it for a pendant fitting I know works).
3. Lamps OK

Coming out of the ceiling there are only 3 wires, Red, Black and Earth, connected to a connector block. Both switches (one at either end of the dining room) are wired the same i.e. Black (No.1), Red (No. 2) and a further Red to Common, in one switch this Red is 'flagged' with white tape.. I cannot see these connections as being the problem, the lights have worked perfectly since the house was built in 1992.

1. Power is getting to the connector block (Red) at the ceiling, when either switch is used.
2. I have checked continuity between the connector block and the switches, using a 'bleep set'. Live OK, Earth OK, but I have *NO* continuity between the connector block and Neutral at either switch.
3. I have also tried continuity between the Neutral at the connector block and all 3 connections in both switches (one Black (No.1), one Red (No. 2), and another Red (Common), I have tried this with both switches turned on and off,

My (uneducated) feeling is that the Neutral connection has 'come adrift' somewhere, *SHOULD* I get continuity between the connector block and the switch(es)? Is my assumption correct if so how can I determine where from. My upstairs floor is made from those large chipboard sheets so it will be a major job to lift them so I would be grateful for any pointers in the right direction before I get the saw out!

Thanks

John

[usenet]

If your wiring is standard then, no, there won't be any neutral at the switches.

My guess would be that it's most likely that the fault is in the connector block in the ceiling above the light, hopefully you'll be able to access that from the hole above the light fitting. The lamp wiring hangs on this (usually) so it is liable to wires pulling out etc.

The other likely place for failure is the switches themselves but, if I understand you correctly you checked these - or have you?

[The Natural Philosopher]

I've found precious little standard in wiring - the two places the incoming feed MAY come to are the switch and the rose(s).

In my house mostly its the switch, and there are connector blocks tacked in there to common up the neutral

[John]

The connector block connections are fine on the 'house end'. Obviously on the 'light end' they have been disconnected and reconnected to the pendant fitting so OK there aswell.

I haven't actually checked the switches internally only the connections to them. I will try a replacement switch but isn't highly unlikely for two

*SEPERATE* switches (10 feet apart) to go at the same time? I would have thought if only one switch has died then the other would still work the lights.

Thanks

John

[usenet]

In the connector above the lamp I would expect a lot more than three wires, have you investigated back into the ceiling space? What is there?

As it's (presumably) a two-way switched light then the failure of one switch will stop both working if the switch fails to 'all open circuit'.

[John]

Not if my understanding of 'star wiring' is correct. All the connections are done at a junction box and a radial out to each fitting, is this not correct. As for checking in the ceiling space, as I said in my original posting my floors are made from large chipboard sheets and I am trying to avoid taking these up unless *absolutely* necessary.

Since my original post I have swapped the switch(es), one at a time, no better, also when the switches (originals) are put in the 'on' position there is power going through the lamp i.e. the Neutral wire at the connector block is now also live, which brings me back to my original thought of a neutral wire has come adrift somewhere.

Thanks

John

[John]

P.S. Since my original post I have swapped the switch(es), one at a time, no better, also when the switches (originals) are put in the 'on' position there is power going through the lamp i.e. the Neutral wire at the connector block is now also live, which brings me back to my original thought of a neutral wire has come adrift somewhere. Another question is are ALL Neutrals in the house linked together in the system? If so can check continuity of the neutral between my ceiling connector and a convenient socket if you see what I mean.

Thanks

John

[Christian McArdle]

Yes. You need to find the main junction box where the unswitched supply and neutral come in. This may be dangling off a short bit of cable not far from the light fitting. If you're feeling lucky, give it a pull and see if it is there. Otherwise, you're going to need to find it. You've already eliminated the switches as being the junction box location.

If you're unlucky, the junction box is buried underneath plaster or something.

Christian.

[Stefek Zaba]

It does sound that way, on a brief half-reading of the symptoms you describe.

Yes, all the neutrals are commoned at the consumer unit's neutral busbar.

If you have a split-load consumer unit, there are two neutral busbars, with the RCBO-side one linked to the pre-RCD one unless the RD has tripped. Similar caveat applies if you have individual RCBOs, which are usually double-pole. Other isolators (such as switched connection units) also isolate the N; in the Olden days sockets were switched exclusively in the L pole, but these days many 13A sockets are double-pole switched, so with the socket switched off the N hole of the socket is also isolated...

HTH - Stefek

[Christian McArdle]

Most RCBOs are single pole switched, aren't they? Perhaps things have moved on since I fitted mine.

Christian.

[ARWadsworth]

Almost certainly a loose neutral.

When you say there are 3 wires at the fitting is this 3 wires inside one grey or white PVC sheathing (i.e. a 1mm or 1.5mm T&E) or are there 2 separately sheathed wires for the back and red (with the earth inside the reds PVC sheath)?

The adrift neutral could be at another lightfitting. Have you swapped any other fittings recently?

Adam

[The Natural Philosopher]

They are in my house.

[John]

Wired in singles

[John]

P.S. Since my original post I have swapped the switch(es), one at a time, no better, also when the switches (originals) are put in the 'on' position there is power going through the lamp i.e. the Neutral wire at the connector block is now also live, which brings me back to my original thought of a neutral wire has come adrift somewhere. Another question is are ALL Neutrals in the house linked together in the system? If so can check continuity of the neutral between my ceiling connector and a convenient socket if you see what I mean.

I have now resigned myself to the need to get the floor(s) up. As I stated they are not traditional floorboards but these 8 ft x 2 ft sheets, large chips on surface, not like 'standard' chipboard. They are, IIRC, nailed down. Has anybody found a successful way of getting these things up without too much damage? I would presume they will be tounged and grooved in some way or other.

Any help/tips greatfully received.

Thanks

John

[Stefek Zaba]

Just been through this in another thread - groups.google.com->Advanced Search is your friend. Summary: chop into it with circular saw set to just over 20mmdepth, or cut-down jigsaw blade, run from drilled starter holes at corners, to achieve similar limited-depth cut. Non-power-tool, sweat-of-brow option is padsaw/padsaw-blade-in-Stanley-knife-handle. Fix battens to sides of hole with countersunk screws from above to replace cutout portion. Watch for fixing nails, joists, cable runs, CH pipes. If money no object, router accessory to cut round access hatches and neat hatch kit is also available...

HTH - Stefek

[ARWadsworth]

Then I take it you mean the latter of the two options and you should be looking for a bad neutral connector on another light fitting (the one that supplies your neutral to the dining room light). Start by looking at the fittings nearest to the dining room to check they have two good neutral connections.

Adam

[Doctor D]

This is how I always do it, but I use a circular saw set to *just* in excess of the depth of the chipboard. Doing this avoids all pipes etc. As well as fixing battens when replacing the panel I fix corner cross pieces diagonally across the hole for extra strength.

Measure carefully before you start cutting - it's always annoying to have the hole miles away from where you want it, and far more time consuming than just banging the floorboard back down and lifting another!

[John]

Thanks for that advice but unfortunately I do not know where I need to get the floor up for access so I will have to take full boards up in the area I

*THINK* the junction box will be.

Cheers

John

[ATC]

Make a hatch in a hidden area close to where you want to check and look in . Hopefully you won't have to cut too many.