Lighting Puzzle

[Bernster]

Hi,

I had some house renovation work done a couple of years back and the electrician provided me new lighting in the dining room-to-be consisting of 6 low voltage down lights and a central single lighting point. Both lighting systems are controlled by a double dimmer switch in the room.

As this work was done prior to decoration and other work he left it so that the 6 down lights were working from the dimmer switch but the central light was what I thought an isolated (taped up) supply from the middle of the ceiling.

My assumption was when I was ready to fit the pendant light it would be a case of turning off the lighting supply , fitting the pendant and off we go. Seems what he left me was not so simple and what I have is the following:

4 cables from ceiling:

• 
  1 x Twin & Earth cable (not connected) which is the unused switch cable (confirmed and tested)
  2 x Twin & Earth white supply cables
  1 x Twin & Earth grey cable which is the in use switch cable for down lights

The 3 cables are connected via connector blocks as follows:

• 
  The black wires from the 2 white cables (assumed supply) connected to the blue wire of the switch cable.
  The red wires from the 2 white cables connected to the brown wire of the switch cable

Any pointers as to how this works or was intended to be configured to supply the pendant light ?

 

[riveralt]

The 3 cables are connected via connector blocks as follows:

• 
  The black wires from the 2 white cables (assumed supply) connected to the blue wire of the switch cable.
  The red wires from the 2 white cables connected to the brown wire of the switch cable

Any pointers as to how this works or was intended to be configured to supply the pendant light ?

Red wires should be your live loop in terminal block.
Black wires should be your neutral loop in terminal block.
Earth wires should be your earth loop in terminal block.

Assuming your dimmer has been wired as normal ie red in C and black(with red sleeve) in L1 then...
At the ceiling
Your switch (red) should be connected to the live loop terminal block- this will take the power down to your switch.
At the ceiling
Your switch wire black(with red sleeve) bringing the power up from the switch should be wired to the brown in the pendant. The returning blue wire from the pendeant should be wired to the neutral loop block. Any earth should be wired to the earth block.

 

[Chri5]

The pendant wire x 2 goes one side to the neutral, otherside to the switch wire. The other switch wire goes to the live.

This then allows the switch to switch the live between supply and pendant lamp.

Old colours red = live, black = neutral, new colours brown = live, blue = neutral.

Don't forget to sleeve and terminate the earth at the pendant rose, even if the earth isn't used it must be added for use on a metal lamp..

 

[ban-all-sheds]

4 cables from ceiling:

• 
  1 x Twin & Earth cable (not connected) which is the unused switch cable (confirmed and tested)
  2 x Twin & Earth white supply cables
  1 x Twin & Earth grey cable which is the in use switch cable for down lights

The 3 cables are connected via connector blocks as follows:

• 
  The black wires from the 2 white cables (assumed supply) connected to the blue wire of the switch cable .
  The red wires from the 2 white cables connected to the brown wire of the switch cable

1. Could you clear up the discrepancies and ambiguities about what is connected to what, as indicated by colour-coding above?
2. What did you do to confirm that the unused switch cable is what you think it is? Is it connected to the dimmer switch?
3. Can you describe and/or post photos of what wires are at the switch?

 

[Bernster]

The 3 cables are connected via connector blocks as follows:

• 
  The black wires from the 2 white cables (assumed supply) connected to the blue wire of the switch cable.
  The red wires from the 2 white cables connected to the brown wire of the switch cable

Any pointers as to how this works or was intended to be configured to supply the pendant light ?

Red wires should be your live loop in terminal block.
Black wires should be your neutral loop in terminal block.
Earth wires should be your earth loop in terminal block.

Assuming your dimmer has been wired as normal ie red in C and black(with red sleeve) in L1 then...
At the ceiling
Your switch (red) should be connected to the live loop terminal block- this will take the power down to your switch.
At the ceiling
Your switch wire black(with red sleeve) bringing the power up from the switch should be wired to the brown in the pendant. The returning blue wire from the pendeant should be wired to the neutral loop block. Any earth should be wired to the earth block.

Thank you Riveralt,

that made sense and was exactly the solution.

I should have mentioned that the earth is present and connected in all cases as the switch and lights are metal cased.

 

[Bernster]

4 cables from ceiling:

• 
  1 x Twin & Earth cable (not connected) which is the unused switch cable (confirmed and tested)
  2 x Twin & Earth white supply cables
  1 x Twin & Earth grey cable which is the in use switch cable for down lights

The 3 cables are connected via connector blocks as follows:

• 
  The black wires from the 2 white cables (assumed supply) connected to the blue wire of the switch cable .
  The red wires from the 2 white cables connected to the brown wire of the switch cable

1. Could you clear up the discrepancies and ambiguities about what is connected to what, as indicated by colour-coding above?
2. What did you do to confirm that the unused switch cable is what you think it is? Is it connected to the dimmer switch?
3. Can you describe and/or post photos of what wires are at the switch?

Hi Ban-all-sheds,

thanks for response, in the interests of any others reading this I will try and clear up any ambiguity.

So, the 4 cables from the ceiling:

• 
  1 x twin & earth cable that is not connected at the ceiling but I confirmed it is connected to the double gang dimmer switch, red to terminal C and black to L1.
  3 x twin & earth cables, one of which is grey and two are white
  connected to the double gang dimmer switch and connected via terminal blocks.
  The 3 connected cables are connected as per the attached picture

I confirmed the 4th cable from the ceiling was the connected to the dimmer switch with a circuit tester.

The 2-gang dimmer switch has 2 twin & earth cables running into it, with red/brown to C and black/blue to L1 and earth to earthing terminal on back box.

 

[ban-all-sheds]

Well - that diagram is nothing like the solution which riveralt gave you, and frankly I don't see how it could work.

If the white cables are carrying the loop then connecting a switch as you have shown it would blow the fuse/trip the circuit breaker and probably destroy the switch as soon as you turned it on.

And if they aren't the loop, where is it?

 

[Bernster]

Well - that diagram is nothing like the solution which riveralt gave you, and frankly I don't see how it could work.

If the white cables are carrying the loop then connecting a switch as you have shown it would blow the fuse/trip the circuit breaker and probably destroy the switch as soon as you turned it on.

And if they aren't the loop, where is it?

The diagram is what has been in place for the last 2 years with a working set of 6 lights from one of the controls on the 2-gang dimmer. I am wondering f it is the end of the loop and so one of the white cables is the feed to the 6 down lights ?

 

[mfarrow]

As BAS has told you, that configuration cannot work, and doesn't make sense.

Are you sure there's not four connectors in the block?

 

[riveralt]

Is your ceiling pendant light working and are you downlighters working?


The problem with the diagram as you have drawn it, is the blue wire coming back from the switch is the switch live (should have a brown sleeve). You have this going into the neutral block which will cause problems.

The blue wire(brown sleeved) should go to the live side of the pendant or downlight your drawing refers to. The returning neutral from the pendant should go to the neutral block.

So your drawing is a circuit without a light at the moment.

.... Having thought about it... is there a terminal block in the switch by chance?

 

[Bernster]

As BAS has told you, that configuration cannot work, and doesn't make sense.

Are you sure there's not four connectors in the block?

I can confirm there is only 3 connectors as shown, plus the 4th cable that was not connected and confirmed to be connected to the dimmer switch.

I tested what Riveralt suggested with a pendant light and now both lights work independently from the 2-gang dimmer switch.

 

[ban-all-sheds]

The diagram is what has been in place for the last 2 years with a working set of 6 lights from one of the controls on the 2-gang dimmer. I am wondering f it is the end of the loop and so one of the white cables is the feed to the 6 down lights ?

So which is the end of the loop?

Is it the bottom white cable with its live & neutral shorted together by the switch, and permanently connected to the top cable which is the feed to the 6 downlights?

Or is it the top white cable with its live & neutral shorted together by the switch, and permanently connected to the bottom cable which is the feed to the 6 downlights?

I can't argue with you that it was working, but I can, and will, argue that it cannot have been wired like that unless the loop ran to the switch and switched live & neutral came from there to that connector block where it split off to feed the 6 downlights, e.g. as 2 sets of 3.

But you say that the only cables at the switch are the two drop cables.....

 

[rebuke]

I think the answer here is that the grey T&E isn't going to a switch, but probably to another connection somewhere, i.e. it's the supply to the downlighters circuit (a 'spur' off the lighting loop if you want)...

Edit to add: metering it might make it appear as a switch cable as if the downlights were in you would have continuity L-N through the bulbs, that would get broken when you turn the switch off etc.

 

[Bernster]

Is your ceiling pendant light working and are you downlighters working?


The problem with the diagram as you have drawn it, is the blue wire coming back from the switch is the switch live (should have a brown sleeve). You have this going into the neutral block which will cause problems.

The blue wire(brown sleeved) should go to the live side of the pendant or downlight your drawing refers to. The returning neutral from the pendant should go to the neutral block.

So your drawing is a circuit without a light at the moment.

.... Having thought about it... is there a terminal block in the switch by chance?

Riveralt,

this is what puzzled me, what is powering the lights, as this seems missing a cable.

I checked and one of the 2 white cables and the top one in the diagram is live feed, the bottom one is not so assume is supply to the 6 down lights.

There could be more to this in the ceiling space but I cannot access this without lifting a fitted wooden floor in room above.

There is an adjacent room with similar lighting set-up. e.g. 6 down lights and 2 wall lights to another double dimmer. I note in this dimmer switch there are 4 drop cables with all blue wires connected into a terminal block. The brown wires go into the switch terminals and link across the 2 sides of the dimmer.

 

[riveralt]

Riveralt,

this is what puzzled me, what is powering the lights, as this seems missing a cable.

I checked and one of the 2 white cables and the top one in the diagram is live feed, the bottom one is not so assume is supply to the 6 down lights.

There could be more to this in the ceiling space but I cannot access this without lifting a fitted wooden floor in room above.

There is an adjacent room with similar lighting set-up. e.g. 6 down lights and 2 wall lights to another double dimmer. I note in this dimmer switch there are 4 drop cables with all blue wires connected into a terminal block. The brown wires go into the switch terminals and link across the 2 sides of the dimmer.

The problem with lighting circuits is that there are many right ways, semi right ways and a number of wrong ways to design them.

When faced with a lighting problem I spend most of my time trying to figure out how the previous guy has wired the circuit up - which is vital to then understanding what the problem is.

Your second dimmer and backbox sounds like it is acting like a jb - in that it has a live, neutral terminal block and earth facility. Normal light switches only have live and earth. It is possible that one of the four cables in this switch is acting as a live,neutral and earth to the first set of downlights but without a significant amount of continuity testing it is difficult to say with any certaintity.

The bottom line is that your downlighters have worked for two years and continue to work without any problem. Furthermore your new ceiling pendant light works as well.

Unless you want to go down the investigative route to finding how the lighting circuits are wired I would leave alone.

If, at the end of the day, you feel there is a problem with the wiring of the lighting circuit, it might be best to get an electrician in to have them checked over.