Light switches with 2 or 3 screws, difference?

[konisaan]

I'm replacing some of the wall switches and sockets with aluminum faces for better visual appeal. You have to buy the switches and sockets separately and fit the plate over. The switches come with either one screw on top and bottom or 1 screw on top and 2 on bottom. Is the extra screw for an earth wire?

I have no experience with this sort of thing and will be paying a tradesman to do the work. I suppose I will have to instruct him to connect the earth wire (if it's available) otherwise he might cut corners.

Is there a way to confirm earth wire connection apart from visual inspection?

[IMHO]

The light switches with 3 terminals will likely be double pole types, used to create 3-way circuits (i.e. can switch a light on/off from two different switches).

[lopburi3]

As said above - normally used for hall/stairs so you can control at both ends.

[konisaan]

The light switches with 3 terminals will likely be double pole types, used to create 3-way circuits (i.e. can switch a light on/off from two different switches).

Ah comprende! Thanks.

So if there is only one switch per light then the third point is just not hooked up and remains redundant without issue?

[KhunBENQ]

It has nothing do with earthing, thats for sure.

I just compared two such switches (I have some on stock here )

Both types have two wire terminals ("holes for the wire) on top and on bottom.

So a total of four terminals,

Lets name them T1, T2, B1, B2).

For both types:

T1 and T2 are fixed by one screw and are electrically connected (conductive),

For the type with one screw:

B1 and B2 are also electrically connected.

Switch position up connects all four terminals.

For the type with two screws:

Switch position up connects B1 with T1/T2.

Switch position down connects B2 with T1/T2.

So the both bottom terminals are connected alternating.

Edited April 2, 2015 by KhunBENQ

[KhunBENQ]

Ah comprende! Thanks.

So if there is only one switch per light then the third point is just not hooked up and remains redundant without issue?

Yep.

You paid too much

Two screw model would suffice.

[KhunBENQ]

The simple model:

two screws. four terminals.

The two top and bottom terminals simply connected respectively.

From here:

https://www.surajit.co.th/vmart/components/com_virtuemart/shop_image/product3/103681.jpg

Edited April 2, 2015 by KhunBENQ

[KhunBENQ]

Own production , the three screw version.

Note that special switch symbol on the middle left (where the terminals are designated as 0, 1, 3 (!).

B1 and B2 each having its own screw of course.

Edited April 2, 2015 by KhunBENQ

[Forkinhades]

OP has been answered, and is happy

//CLOSED//