3way/intermediate light switch

[stanwilcock]

Can someone please explain how light switching can work for three different levels of a building. We have a switch downstairs, a switch on the first floor and a switch in the loft all working the same lights. I need to change the middle light switch, what is this called and how does it all work. Thank you all in advance.

[kempie]

The third (intermediate) location is controlled by a 4-way switch.

An explanation of how the circuit works is given here.

[qapmoc]

I have to admit thats a pretty good explanation of the circuit functions.

[pedderwo]

The middle switch is the intermediate switch. Basically is works just like a 2-way except that the switch has 4 connections in the form of an X. Imagine the points of the X numbered from the top left clockwise 1.2.3.4. 1&3 are making contact, when you switch over the switch 2&4 then make contact.

There will be a switch wire at one end (2-way) switch and a live at the other end.

[pedderwo]

But most times the switch wire (one core of the cable from the light itself) first goes to the first switch and connected (behind the switch) to a core of a 3 core cable which then goes to the intermediate. At Switch One the other 2 cores of the 3-core, called strappers are connected to L1 and L2 with a live (from a seperate cable feed) at the top of the switch (Common). The 3 core then goes to the intermediate switch and the strappers are connected at points 1&2 with the 3rd core connceted behind the switch to the 3rd core of another cable that goes to switch 3 (2-way).

[pedderwo]

At the intermediate the strappers of the cable to switch 3 are connected at points 3&4.

At switch 3 the strappers are connected at L1 & L2 while the core that has been connected through connects into 'common'.

Back to switch 1 where the cable from the light (2 core). One core has been sent all the way to switch 3, the other will be the Neutral which will connect to the Neutral feed.

This sounds okay in my head but does it make sense?

[pedderwo]

Sorry about the three answers, AB wouldn't let me post it as one.