Replacing 2 gang light switch

[ormerods]

We're replacing the light switches and plug sockets in our living room, the plug sockets were easy enough but I was looking for some guidance with the light switch.

The old switch has 4 terminals (see photo)
The new switch has 6 terminals + earth (see photo)

I'm guessing the common wires go into COM1 and COM2?

I'm just a bit unclear about L22 L21 L12 L11 - what do these mean?

I assume I should also be connecting the earth terminal to the metal back box?

 

[Jurassicspark]

Red wires to COM 1 and COM 2. Get a short bit of 1.5mm wire and interlink from COM 1 and COM 2 on the new switch.

The wires at the bottom - One in L11 and the other in L21.

I assume I should also be connecting the earth terminal to the metal back box?

Yes.

 

[securespark]

It looks like the wiring and back box are pre-14th Ed.

If this is the case, you should change the switch for a non-metallic one.

 

[EFLImpudence]

Red wires to COM 1 and COM 2. Get a short bit of 1.5mm wire and interlink from COM 1 and COM 2 on the new switch.

The wires at the bottom - One in L11 and the other in L12.

Yes.

Are you sure?

 

[Jurassicspark]

Are you sure?

It looks like it. OP should send clearer pictures. The small bit of black wire looks like it's connected to both of the commons of the old switch.

 

[ericmark]

The use of either L11 or L12 will change if the switch is up or down for on, but either will work, the same with L21 and L22. So two terminals are left without any wires, which means basic same as the old switch.

As @securespark says pre-1966 we did not earth the lighting circuits with non-metallic fittings, and lamps had to be filament type. So to use LED lamps, in theory pre-1966 wiring needs to be renewed. In real terms, we want RCD protection for the lights, and all plastic fittings, with bungs that fit into the screw holes, before 1966 we had wooden back boxes.

Safety must come before what it looks like, I had the same problem with parent's old house, even when built it did not comply, as it had wall lights fitted, and pre-1966 rules only allowed no earths to lights if using "Lighting fittings using filament lamps installed in a room having a non-conducting floor, mounted at such a height that they cannot readily be touched and are out of reach of earthed metal." The filament lamps were to stop one using fluorescent lamps, as they needed an earth. But a tungsten lamp one could not touch while switched on as they would burn you, with LED they are cold, so one could change a bulb while live, so these need an earthed system.

 

[sparkwright]

Can't see any earth wires - if there aren't any, you can't fit your new switch.

 

[sparkwright]

The wires at the bottom - One in L11 and the other in L12.

Would you like another run at that?

 

[Jurassicspark]

Would you like another run at that?

Just realised the typo from typing too fast!

 

[Jurassicspark]

@ormerods - Get a 2 way 2 gang plastic switch. Noticed you wiring is very old.

 

[sparkwright]

The use of either L11 or L12 will change if the switch is up or down for on, but either will work, the same with L21 and L22. So two terminals are left without any wires, which means basic same as the old switch.

As @securespark says pre-1966 we did not earth the lighting circuits with non-metallic fittings, and lamps had to be filament type. So to use LED lamps, in theory pre-1966 wiring needs to be renewed. In real terms, we want RCD protection for the lights, and all plastic fittings, with bungs that fit into the screw holes, before 1966 we had wooden back boxes.

Safety must come before what it looks like, I had the same problem with parent's old house, even when built it did not comply, as it had wall lights fitted, and pre-1966 rules only allowed no earths to lights if using "Lighting fittings using filament lamps installed in a room having a non-conducting floor, mounted at such a height that they cannot readily be touched and are out of reach of earthed metal." The filament lamps were to stop one using fluorescent lamps, as they needed an earth. But a tungsten lamp one could not touch while switched on as they would burn you, with LED they are cold, so one could change a bulb while live, so these need an earthed system.

There was a long cross over period between wooden switch boxes, and metal switch boxes (generally with the nylon lugs).

You could certainly get metal back boxes for switches long before 1966. Mid 50s, probably.

Indeed the purpose of the nylon lugs was because the lighting circuit would seldom have an earth connection.

One of the weirdest things I have seen during the various cross-over periods with new materials was plastic oval conduit used with wooden back boxes. Looks odd, the old combined with the new.

 

[sparkwright]

.

 

[ericmark]

I was rather surprised when I came to work on my parent's house to find no earth. It did have one when I was a boy, as I ruptured a fuse in the plug with a line - earth fault, but around 2004 my mother lost her leg, and the firm fitting in the wet room ran off into the Welsh hills, and my son and I were left to sort it out.

The only earth I could find, was the GPO party line phone. All I can assume was it was earthed with the water supply until it was changed for plastic, gas arrived late, so no gas when I was a boy.

We asked the DNO what earth we should have, they did not know, so had to visit to find out, and left us with a TN-C-S earth. But had I not tried to use the loop impedance meter, I would have likely been unaware there was no earth.

The builder had brought in someone he claimed was an electrician, he arrived with no test gear, swapped the fuse board for a consumer unit, and then could not get the RCD to hold in, and ended up fitting an isolator instead of the RCD, using our insulation tester, we quickly realised the house needed rewiring, but dad would not let us get it done, had to wait until he died, and took the opportunity when mother was in hospital to get it done.

We actually found most of the faults were with wiring added by my dad, spur off spur off spur etc. But it did point out how important inspection and testing is, which is often missed with DIY work.

 

[securespark]

One of the weirdest things I have seen during the various cross-over periods with new materials was plastic oval conduit used with wooden back boxes. Looks odd, the old combined with the new.

I have a board with samples of cable over the years that I made as a teaching aid.

One of them is rubber lighting T&E with a single strand cpc.

Edited as I forgot to specify

 

[FrodoOne]

Please permit me to make one or two "observations".

Photo #1 in Post #1 is
https://www.diynot.com/diy/attachments/new-switch-png.347620/

While I cannot see the front in this picture,
it seems probable that the (plastic encased) switch(es) are mounted on a "plastic" face-plate and
affixed to this face-plate is a decorative metal finish.

Without the deliberate connection (riveting) of the mounting screw holes to this face-plate, the metal surface would be insulated from any other "metal" able to come in contact with an "electrical supply" - by a fault condition.

If the mounting screws were to be "deep set" in the "body" of the switch-plate
and
the face plate to be a "Snap-On" cover-plate,
it world not be possible to touch the screws except with a tool - such as a screw driver - after removing the cover-plate.
There then would be no need (or possibility) to Earth this decorative cover-plate.

Most of you "regulars" will see where I am going with this !

An Australian four gang wall plate - cover removed - is shown in

File:Australian four gang wall plate - cover removed.jpg - Wikimedia Commons

commons.wikimedia.org

and
https://commons.wikimedia.org/wiki/File:Australian_four_gang_wall_plate.jpg
shows an Australian four gang wall plate - with cover.

When the "cover removed" photo was taken, it was thought sufficient to leave the deep-set screw hole as is, because it would be covered by the cover-plate.
This has now been changed and such switch-plates are now provided with "flush caps" and other "covers", of various designs.
"Flush Caps" are available to cover the "Deep Set" screws , in older switch-plates if they have been removed - as they often are !!!!
https://tle.mmem.com.au/hpmflushcaps

My point in this is that it is possible to design
insulated switch "cover-plates" for "switch-plates"
even with metal covers,
which are isolated/double-insulated away from any likely electrical connection.

If one country in the world has managed to do that (over the last 50 years - or more), why have not others,
with the same manufacturers providing such products (Legrand and Schneider among others.)?

Here is an el-cheapo cover-plate, with no screw holes and no Earth connection, possible or needed.
https://www.bunnings.com.au/deta-s-line-brushed-aluminium-4-gang-switch-cover-plate_p0288828

While the Earth is required at the Luminaire in Australia it is not required/needed at the switch.
Hence, with a "switch loop" connection, only single pair cables are required (No Earth wire.)
Hence the availability of Two Core electrical cable
https://www.bunnings.com.au/cable-elect-2core-twinact-p-m-1-5mm-cacp05a1002wvab-1m_p4430137
with a "Colour Code" which does not require "sleeving" - with "White" indicating "Switched Line".

However, "these days" having Line and Neutral at the "Switch" is becoming more "desirable" - for other reasons.
When the Line and Neutral are provided at the Switch, for on-wiring to the Luminaire, Twin and Earth would be used for "Supply" and Twin and Earth wired to the Luminaire, although the Earth would not (could not) be utilized at the Switch and is just "through-connected" there.