oh no, it's that two way switch again

[miss_novice]

As you can tell by my sign in name, I am really new to this wiring lark. I've been trying to have a go at this problem myself for a week, and after searching for hours on web have found this site and looked through every 2 switch problem on here. Nearest one to my problem was 2 way switch again! from Peter CFC but I've tried the solution to that and, no joy. I've swotted up on electrical terms - so will someone just check that I've got this right and I'm not being dim

2 gang - 2 buttons (toggles in my case)
2 way - switches on/off in two locations

OK, here's wot's going on. Hall/stairs with two ceiling lights. Upstairs - one gang, one switch which turns upstairs hall light on and off. Downstairs - two gang, two switch which should have one switch turning downstairs light on/off, the other switch should turn the upstairs light on/off.

Wiring - two 3 core wires, each with a black and a red, with both earths in one green/yellow sheath connected to the metal box.

When I took the old switch off I did one wire at a time and put them into the same position on the new switch. Didn't work. Can't remember 100%what was going on but as far as I recall both lights worked but downstairs switch only worked when upstairs switch was either on or off. The only thing I remember about old switch wiring was that one red was in the common at the top, the other was into one of bottom holes on the other switch and there was a piece of red wire connectng both common holes at top.

I've tried putting wires for bottom light as follows - into the switch for downstairs with red in common at top, black into L1. This works the switch downstairs. For the other switch, which should be for upstairs light, have done the same, red in common and black in L1 - not working. Also tried black in L2, not working. So upstairs light is only working with upstairs switch.

Any of you guys out there able to help me? I did think that perhaps I need to link the two L1 holes, and L2 holes between the two switches (as per the diagram that came with the new switch) but not sure how this is going to work - what happens with the two black cables from the wires in the box? HELP!

 

[plugwash]

before 3 and earth became popular people did 2 way siwtching in all sorts of ways

from you descriptions i take it by 3 core you mean twin and earth cable

my guess is that one of those wires is a normal switch cable for the downstairs light it should be easy to figure out which by wiring a switch to each one in turn ( in that cable red is probablly live black is probablly switched live)

then the live (red wire) from that is borrowed and taken to the common of the other switch

and the L1 and L2 from that go via the other cable to the lightswich on the landing and on to the landing light

that will make it work but it may not be a compliant installation....

with such a setup you need to find out where the neutral of the landing light comes from if it's comeing from the upstairs lighting cuircuit you have a borrowed neutral which is very bad practice and needs to be dealt with

and if you have singles (that is single cores with only one layer of insulation) that are not in conduit you have another issue that needs dealing with

 

[miss_novice]

Ok, thanks for the quick response but you really have lost me now. I think I better give up on this and get a sparky in to help me, bit concerned about the couple of issues you have mentioned.

Are you saying that the red that works the downstairs light should go into the common switch that operates the upstairs light? Is this why there was a small piece of red wire linking the downstairs common to the upstairs common on my old switch? What should I do with the other red wire - should that go into the L2 of the switch for upstairs light?
By the way, I live in a new house so I would have thought my wiring would be OK. Mind you, it was built by some cowboy outfit so I wouldn't be surprised if it wasn't.

I can't believe I'm having so many problems - I did fit a new 2 gang 2 way dimmer switch in my living room with no problems.

Feeling a bit dim (ha, ha, excuse the pun)

 

[plugwash]

yep that is what your short red wire was for

red and black of the cable to upstairs go into L1 and L2 of the switch for upstairs

and the live feed is being borrowed off the cable from the downstairs light

this should make it work but it probablly still won't be up to spec

 

[MANDATE]

You appear to have the switch for the downstairs light wired correctly, which is a two way switch,but you're using it in a one way mode ie L2 is not being used.
The other switch is also a two way switch and you need to use it in the two way mode if it is to function in conjunction with the switch upstairs, which also must be a two way switch. These two switches must be connected to each other as well as the light, but how is it done?
Well there are two methods completely different.
See if you can follow this for method 1
Live ( red) goes to com at switch A, this comes from light.
Wire ( colour?) goes from L1 on switch A to L1 on switch B
Wire ( coulor ?) goes fro m L2 on switch A to L on switch B
Switched live (black) leaves com on switch B to go to light

The other method has the live (red) and switched live (black) both going to switch A. Red to L1 black to L2.
This time there are three wires linking the two switches.
com to com (red) L1 to L1 (yellow) and L2 to L2 (blue).

I suspect yours is method 1 and and the incoming ( live) instead of coming down from the light, it comes from the adjacent switch using a short wire to feed it from com to com.
So it all seems to make sense. You have a red and black for the one way switch (com/L1) and a red and black for the two way switch (L1/L2 ) and the link from com to com.
No doubt you could check the upstairs switch which will have wires in L1 and L2 (linking the switches) and also a wire in com going to the light.
Three wires in total.

 

[ban-all-sheds]

A picture is worth, etc...

Have a look at the second diagram on this page: here and see if it helps.

And as plugwash says, if the upstairs light is fed from the downstairs circuit, or vice-versa, make absolutely sure that it also gets its neutral from the same circuit, not the other one where it physically is just because it's handy.

 

[miss_novice]

Cheers guys, I think I'm getting it now. Not been able to try it tonight cos it's gone dark but will do so tomorrow. Plugwash, your explanation was really easy to follow and makes sense. Ban-all-sheds - thanks for diagram, a lot like the one I got with the switch. The penny is finally dropping!

Gonna check my upstairs light - got a feeling that might be where there is a problem too. I'll let you know how I get on.

 

[miss_novice]

Got it sussed, and it's worked - I've not blown us all up. Plugwash - thanks for your clear and easy to follow instructions. Miss Novice is now a beginner!

 

[ban-all-sheds]

Excellent.

What was the problem?

 

[miss_novice]

I think I must have put the L1 and L2 wires around the wrong way on the downstairs switch. Checked the upstairs light, it was wired up fine. Have put the small piece of wire in to link the two com's from downstairs light switch into switch downstairs which works the upstairs light. (How it was originally).

The problem all along was that I didn't know what I was doing and didn't understand how it all works and how they need to link. Wasn't reading the diagram in my instructions right either. Thankfully, I'm a little bit wiser now.

Cheers