Bizzarre connections in old light switch

[squeekykilt]

Hi All,

Just looking for a bit of advice.

I am in the process of renewing some old light switches in my house that have become worn-out. One is a two-gang switch controlling a ceiling light on one switch and a set of wall lights from the second switch. (it is an old MK brand affair in a modular construction with the two separate switches one above the other in a framework screwed to the back-box)

However when I have removed the faceplate to check the wires, I discovered something a bit strange - both switches are served by two-core cable (brown + red) as expected however there is a length of red wire going from the L1 terminal of the top switch to the L1 of the bottom switch, and I cant work out why it is there! (The lights work independantly so why the link?) Should this be transferred to the new switch that I install
as my gut instinct is that it shouldnt be.

Any ideas anyone???
Thanks.

 

[Lectrician]

You have a commoned live supply down to the switch, and two returning switched lives - very common practice.

You say you have the 'usual' red and brown........??? Thats un-usual. Brown/Blue or Red/Black.

Usually, a switch like this would be served with a 3 core and earth cable.

 

[squeekykilt]

You have a commoned live supply down to the switch, and two returning switched lives - very common practice.

You say you have the 'usual' red and brown........??? Thats un-usual. Brown/Blue or Red/Black.

Usually, a switch like this would be served with a 3 core and earth cable.

Ok thanks for the explanation. As long as that is a legitimate arrangement of wires then thats ok.

The wires may actually be red and black (they are covered in a bit of dust so that may well have made them look brown!) Will give them a dust off when I fit the new switch.

Thanks.

 

[squeekykilt]

You have a commoned live supply down to the switch, and two returning switched lives - very common practice.

So just to get this straight, am I correct in thinking that means the live feed from one light is "feeding" power to the live of the second light on the other switch. Or have I totally misunderstood that?

Usually, a switch like this would be served with a 3 core and earth cable.

Why three core and earth, I thought that was only neccessary for a two-way circuit?

Thanks

 

[dingbat]

I am in the process of renewing some old light switches in my house that have become worn-out... (it is an old MK brand affair in a modular construction with the two separate switches one above the other in a framework screwed to the back-box)

If that is what I think it is then there's a real chance your lighting is lacking an earth. Those switches are ancient and you should really get your wiring checked out by a professional. (If you have any Class I fittings and no earth you have no protection whatsoever from a fault causing exposed metallic parts to become live.)

 

[Lectrician]

I though it sounded like the old school grid, with a double architrave box?

 

[squeekykilt]

If that is what I think it is then there's a real chance your lighting is lacking an earth. Those switches are ancient and you should really get your wiring checked out by a professional. (If you have any Class I fittings and no earth you have no protection whatsoever from a fault causing exposed metallic parts to become live.)

From what I have seen when I took the faceplate off, it looks like you are correct about the lack of earth.

What do you mean by "Class I fittings"? (sorry im not 100% up on the terminology)

 

[squeekykilt]

I though it sounded like the old school grid, with a double architrave box?

It certainly looks like an older version of the current MK Grid plus system, with the separate switches, mounting box and faceplates.

 

[dingbat]

Class I fittings - anything that has exposed metallic parts that are not double insulated. Most modern replacement light fittings, for instance.

If the light circuit is that old (since 1966 an earth has been required on lighting circuits) how's the rest of your installation?

It's a false economy to rewire in stages. If it needs it (and it sounds like it's overdue) get it done before any fancy ideas about decor.

 

[squeekykilt]

The current faceplate for the switches has become damaged hence the need for the replacement.

In the interim before I can get the whole installation checked, will it be relatively safe to wire up the new switch with the red wire connecting the two L1 terminals (i.e the commoned live referred to by Lectrician) and all other wires to the same terminals in new switch???

Thanks.

 

[plugwash]

as there is no earth make sure you use a plastic switch and if the box is metal and doesn't have insulated screw lugs use screwcaps (or at a pinch if you don't have any screwcaps some kind of insulating sealant).

its a good use the existing screws to mount to the backbox, i'm not sure when accessory box screws changed to metric but i'm pretty sure they weren't metric sized originally.

i'd also be tempted to completely sleeve the wires with red or brown sleeving especially if you think the insulation migt be rubber (old rubber can fall apart soon after being messed with even if it looked fine before).

given all that you should have a repair thats as safe as the rest of the install but i agree that the installation as a whole should be checked out and either the lights or the complete install rewired ASAP.

 

[squeekykilt]

Thanks Plugwash,

The replacement switch I have bought is a plastic one, thogh not sure that the screw lugs are insulated - will have to check.

The screw sizes shouldnt be a problem as need to replace the backbox at the same time as current switch sits in a vertical two-gang box, so have bought new metal pattress too.

Will pick up some sleeving on my way home tonight to cover the wires before I connect them up.

So the commoned earth is acceptable and safe to re-connect when I do the change then? I.e I can transfer the connections exactly as they are in the existing switch with the separate red wire connected between the two L1 terminals as at present?

Thanks.