Replacing 4 term 2 way switch with a 3 term 2 way switch

[s_rashid]

Hello Guys,

I have an old two way switch with 4 terminals (2 at the top for L1 and 2 terminals at the bottom for L2). There are three wires at the back of this two way switch, Black, Earth (dark green sleeve - no yellow color on the sleeve) and Red. Top two terminals (L1) has Black and Earth (dark green sleeve) wire and the one of the bottom terminals(L2) has Red wire

When the light is switched on - using a basic scredriver tester all three wires is indicated as live. On the other end of the two way switch (this is a new three terminal switch with new color wiring - 3 core and earth); all three terminals are live(with screwdriver tester) as well.

When the light is switched off; on new switch(three terminals); the common terminal is live and one of the other two terminals is live. On the old two way switch on the other side ( 4 terminals); Earth (dark green sleeve) is live and RED (connected to one of the bottom terminals - L2) is live.

Two way switching works fine. Functionally the circuit works fine.
Couple of things:

1) How do i replace the old 4 terminal switch with a new 3 terminal switch; really looking for which of the 3 wires would go in the COMMON terminal of new switch and which one for L1 and L2.

2) Technically; should the old two way switch side really have three core and earth? I understand this side doesn't have any wire connected to the earth and is a possible safety risk(?) AND will this fail the electrical certification (Part P regulation stuff) on this basis?


****** One another question urelated to above *****

There is another switch; where the flush metal box(single switch) in the wall; out of the two screw holes (for screwing on the switch plate) has a half broken screw with no head only stem; this is an issue as i can't get that screw out; is there a way to remove this screw; the room has been painted and don't really want to replace the metal box with a new one.

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Any help in this regard would be greatly appreciated. Thanks in advance.

 

[breezer]

picture?

 

[ColJack]

your 4 terminal switch is actually an intermediate switch, but they can be used as 2 way..

the use of the earth wire as a live conductor is never a good idea an as such it's highly recomended you change the wire or get an electrician in to do it for you..

that being said, it's as easy to change the intermediate for a 2 way as it can possibly be in this situation..

the red is live and should go in the COM or C terminal if your 2 way is marked as COM / L1 / L2, or in L1 if your switch is marked as L1 / L2 / L3.

the black and "ahem!!!" green should go in the other 2 terminals..

in the type of 2 way lighting circuit you have, it's perfectly normal for all 3 wires to be live when the light is on..

as for the broken screw, it's pliers time..
if it won't come out, then try screwing it in a bit first to loosen the threads..

 

[s_rashid]

Thanks for your reply ColJack much appreciated !!! I was wondering if this wiring arragement would fail Part P testing (electrical certification), is it a safety risk (under what circumstance(s))?.
The other thing is; the broken screw doesn't have any head to it; there is barely a two thread rounds in front of the metal box screw hole.

Cheers

 

[Click-Sure]

Damn good reason behind not using the earth/cpc wire as a live wire.

What happens if a live cable shorts to the backbox (and the metal screws) making it all live, no protective device (well, RCD, just possibly, but not a common find on lighting circuits pre-17th ed, except in a TT) will disconnect the juice!

Nylon screws (you're a better man/woman than me if you can get them to work well with cheap-o galvanised back boxes. Screw covers are not an option.

I'd certainally flag it up on a PIR, with similar severity to a lighting circuit with no CPC.

 

[ColJack]

going with a similar theme...

I have in my house, a 2 way light switch that is wired in 2 single core and earth cables..

the "live" cable has it's earth used as as earth, and the strapper cable has the earth used as a switch wire..

since there is an earth at the switch, would you still flag it?

(BTW, this was how it was when I moved in and entails chasing out roughly 15 foot of plaster to change as it's in the ntrance hall stair well.. )

 

[s_rashid]

Thanks once again for the response Click Sure and ColJack.

Click Sure -

"I'd certainally flag it up on a PIR, with similar severity to a lighting circuit with no CPC"

Does this mean that the Eletrical certification or PIR would fail( in other words would i need to get this rectified inorder to get my electrics certified)?

Kindly suggest any tip(s) to get the headless screw out of the backbox screwhole. Changing the box is not something i really want to do on a newly skimmed wall.

Cheers.

 

[RF Lighting]

Does this mean that the Eletrical certification or PIR would fail

Yes

( in other words would i need to get this rectified inorder to get my electrics certified)?

Yes

Kindly suggest any tip(s) to get the headless screw out of the backbox screwhole.

Change the back box

Changing the box is not something i really want to do on a newly skimmed wall.

Oh dear