changing old light switches for new

[samsondel]

Simple I thought! Wrong. My old light switches are cabled in red and black and operate one common 2 way light and 1 other independent light each. The upstairs switch has three connectors at the top marked ABB and three at the bottom marked AAB. Three cables come into the box - cable 1 has the red line not connected and the black line goes to the B connector on the bottom row (AAB). Cable 2 has the red line going to the A connector on the top row (ABB) and the black line goes to goes to the first A connector on the bottom row (AAB). Cable 3 has the red line going to the middle B connector on the top row (ABB) and the black line goes to the other B connector on the top row (ABB).
The switch downstairs has the same AAB and ABB connectors but the wiring is different. 2 cables come into the box. Cable 1 has the red line going to the B connector on the top row (AAB) and the black goes to the outside B connector on the bottom row (ABB). Cable 2 has the red line going to the outside A connector on the top row (AAB) and the black line goes to the middle A connector on the top row (AAB). There is also a red line connecting the B connector on the top row (AAB) to the A connector on the bottom row (ABB).
My new switches are from Focus and have 2 banks of connectors with 3 openings in each. The openings are not marked in any way I can read although there seems to be one marked with 50Hz, one with BSEN 60669 and one marked GB 18916. I think these are just manufacturing numbers.

Can anyone please suggest a safe wiring layout for each switch so that I don't blow the fuses or myself up. Thanks

 

[mikeyd]

Does the new switches show any lines which might suggest that half of the terminals are for one switch and the other half for the other switch? - Something like a diagonal line like either of these:

[code:1]
---O---O---O--
| \ |
| \ |
| \ |
| \ |
| \ |
---O---O---O--



---O---O---O--
| / |
| / |
| / |
| / |
| / |
---O---O---O--
[/code:1]

If there are and they match the top example then wire it exactly as your previous switches.
If they look like the second example then the wires in the top row of your old switch needs swapped with the bottom row.
It sounds like you only have lives and switched lives in the switch so you should not worry about blowing fuses.

 

[JohnD]

"The upstairs switch has three connectors at the top marked ABB and three at the bottom marked AAB"

You may need to draw this on a bit of paper to see what I mean...

A single, one-way switch has one terminal at the top and one terminal at the bottom (easy!)

A single, two-way switch has three terminals arranged in a triangle... one terminal at the top and two at the bottom (so it sends the power from the top one, to one or other of the bottom ones.... hence two way) (fairly easy!)

If you want to use a two-way switch as a one-way switch, you just go in through the single terminal at the top and out through either (but not both) of the two at the bottom.

- however, if you turn the two way switch upside down, it obviously now has two at the top and one at the bottom. The power still goes in through the single and out through one or other of the two. (still fairly easy)

But...

A Double two way switch, is composed of two single two way switches in the same moulding. each has three terminals. In order to confuse you, the makers often arrange the terminals so that one of the switches has one terminal at the top and two at the bottom, and the other has to terminals at the top and one at the bottom. If you didn't know how it was constructed, you would just see three terminals at the top and three at the bottom.

Now you know how it is made, you just have to look at the back of your double switches and identify which are the three terminals for the left-hand switch, and which are the three terminals for the right hand switch.

See what I mean? If not, draw a single two-way switch on a bit of paper, and another single two-way switch on another bit of paper. Cut them out and stick them together.

 

[samsondel]

Mikeyd - thanks for response. No markings on the old or new switches like the ones in your sketch.

 

[samsondel]

JohnD - thanks for response. I'm struggling with the new switches because there are no markings to identify which connectors are for either of the two switches. I've decided to take the switches back to Focus and try to get ones that are at least marked - failing that I will find an electrician.

 

[Space cat]

Start by identifying which terminals belong to which switch in your new ones. The usual arrangement is for each switch to have two terminals at one end and one at the other. The single one is CoMMON, COM or just C. The two at the opposite end are L1 and L2. Are you sure there are no such markings? From your existing wiring we can see that the old switches were functionally the same but labelled differently. A single A in a row of three is COMMON. The two A's in the opposite row are the L1 and L2 that go with it. Ditto for the B's.

On your downstairs switch, connect the short wire between the two COM's. Cable 1 red goes to one of the two COMs and black goes to either L1 or L2 opposite. This switch will not be part of the two way circuit. If it works upside down move black to the other L. Connect cable 2 red and black to L1 and L2 respectively on the other switch.

On your upstairs switch, connect cable 2 red to one of the COM's and black to either L1 or L2 opposite. This switch will not be part of the two way circuit. If it works upside down move black to the other L. Connect cable 3 red and black to L1 and L2 respectively on the other switch. Finally, connect cable 1 black to the COM terminal opposite.

You won't blow anything up if you get it wrong but you will find that lights don't work as expected. Make sure you can get all the wires back into their original holes in case you have to start again from scratch.

 

[JohnD]

if you buy yourself a multimeter for about £10, we can explain how to identify terminals on a light switch. It can also be used for lots of other things, including identifyig which of half a dozen wires in a ceiling rose is which.

Most light switches will have the terminals marked "COM" "L1" and "L2" as space cat says.