Adding addition light and switch. Lamp only receiving 80v

[stringman]

Hi all

I have read the page
https://www.diynot.com/pages/el/el032.php as I wanted to add a separately controlled ceiling light in the bathroom.

Firist I changed the switch (well a lightwave dimmer) to a 2 gang. fed a new 1.5mm twin and earth to the ceiling.
Then I located the existing junction boxes that are used for the wall lights.
There was one junction box with the switchwire going in and another twin and earth coming in from another room.
They are joined red to brown(new grey twin and earth) black to blue and earth.
when the switch is off I get 230v between red and black and 230v between red and earth

when the switch is on I get 56v between red and black and 230v between red and earth

the next junction box has a twin and earth going to the lamps and a another disappearing to another room.
Light switched off and 0 v between live and neutral and also between live and earth

switch the light on and the voltage goes to 170v !!

This was all discovered after following the instruction on the linked page.
I split the feed to get my "loop through" feed, put that into some choc bloc to test the light (replicating a ceiling rose) fed in my switch feed and connected my lamp.
the lamp worked but was very dim and low and behold the feed to the lamp was 70v

Any ideas what on earth is going on??

many thanks

 

[echoes]

Sounds as if some lamps have got wired in series.
May we have some photos inside your junction boxes, switches and anywhere else you've been, showing what's connected to what?

 

[ericmark]

I would guess you have used a black or blue wire as a neutral when in fact they are switched line, so you have ended up wiring in series instead of parrellel.

 

[stringman]

I have discovered the answer to one of the issues!! it appears that Lightwave dimmers only output around 180v even when running at 100%
so that's the reason for the first batch of problems.
Not sure if you chaps were kindly answering the first or the 2nd problem.

I will have a go at photos but I am not sure where anything goes as the previous owner did the electrics.
What I want to achieve, though, is have a new ceiling light on a separate switch. so am I correct in thinking that in theory I need to find a live lighting circuit cable, which I then "break into) from this I take a live into the switch and then back out and then into the ive of the light (via a rose or connector) and take the neutral from the lighting circuit again to the live and then join all the earths.

Many thanks

 

[echoes]

I'm now slightly confused.
Is this correct...
You've changed a one-gang switch or dimmer to a 2-gang dimmer switch to control a newly installed lamp?

I need to find a live lighting circuit cable, which I then "break into) from this I take a live into the switch and then back out and then into the live of the light (via a rose or connector)

So far, so good... All these connections can be made in a single junction box.

...
and take the neutral from the lighting circuit again to the live and then join all the earths.

No. You must connect the neutral at the lamp fitting to a neutral of the lighting circuit.

Edit: did you have twin + earth, or 3-core + earth at the *original* switch? I.e. Do you have a neutral at the switch, or just live & switched live?

 

[echoes]

I will have a go at photos but I am not sure where anything goes as the previous owner did the electrics.

Just photos of anything to which you have made additions or alterations.

 

[stringman]

I'm now slightly confused.
Is this correct...
You've changed a one-gang switch or dimmer to a 2-gang dimmer switch to control a newly installed lamp?

No I have installed a two gang dimmer so that I can dim the existing wall lights and then add in the ceiling lights so it is in effect s systems


So far, so good... All these connections can be made in a single junction box.



No. You must connect the neutral at the lamp fitting to a neutral of the lighting circuit.

Edit: did you have twin + earth, or 3-core + earth at the *original* switch? I.e. Do you have a neutral at the switch, or just live & switched live?

Sorry that was a typo I did mean take the neutral from the live circuit and join that to the neutral of the lamp. as I see it you effectively T off the light circuit but put a switch on the live.
But that does make me think!
looking at it as if it was a choc bloc instead of a ceiling rose I had this:

1 Live in from main circuit Feed Out to switch
2 feed in from switch (live) live feed out to lamp
3 Neutral in from main circuit Neutral feed out to lamp
4 Earth from live circuit earth from switch wire, earth to lamp

How I broke the main circuit was to take the feed (which is permanently 240v) to the existing lamp (which was where it also connected to the switch wire (which is where I think I am going wrong) and T off to by choc bloc as above.
I wonder if that is whats causing me problems?

 

[echoes]

Those photos are going to save a lot of time!

 

[ban-all-sheds]

I have discovered the answer to one of the issues!! it appears that Lightwave dimmers only output around 180v even when running at 100%

Really?

Why would they make it do that?

 

[JohnW2]

Really? Why would they make it do that?

I don't know about the 'new fangled' (i.e. modern) ones, but some of the simplistic dimmers of yesteryear were unable to to produce 100% brightness (which roughly equates to "average voltage 100% of supply voltage) - with the very simplest (those which used a thryristor/SCR, rather than TRIAC) had a theoretical ceiling of 50%.

Kind Regards, John

 

[echoes]

Hey @JohnW2 , you'll like the earthing requirements: "Not essential (double insulated)"

 

[JohnW2]

Hey @JohnW2 , you'll like the earthing requirements: "Not essential (double insulated)"

Yep. I would regard that as a very sensible statement

Kind Regards, John

 

[stringman]

so I have a couple of pics taken this are not changes I have made but are the junctions as I found them.
The 1st one The one with the nailclippers in the edge shows the grey cable going to the switch and the white cable that goes under the floor to another room.
The 2nd picture shows a white cable that comes from under the floor from the same room as the other white cable and the grey cable that goes to the lamp.
the only actual change I have made is swap over the switch (the wiring is the same)
The lights work (albeit showing 180v - but we don't talk about that lol)
but when I added another light to the system as per the linked page (I tried many different ways) I could only get a very dim illumination 70 v.

 

[echoes]

I split the feed to get my "loop through" feed, put that into some choc bloc to test the light (replicating a ceiling rose) fed in my switch feed and connected my lamp.

That's what I would have liked a photo of.

 

[winston1]

I don't know about the 'new fangled' (i.e. modern) ones, but some of the simplistic dimmers of yesteryear were unable to to produce 100% brightness (which roughly equates to "average voltage 100% of supply voltage) - with the very simplest (those which used a thryristor/SCR, rather than TRIAC) had a theoretical ceiling of 50%.

Kind Regards, John

I have a dimmer from yesteryear (around 1969 if I remember) and its SCR is fed by a bridge rectifier and can achieve full brightness. In fact never seen one that only gives 50%.