Quick question regarding intermediate switch.

Hi, just built a conservatory but I want to crack on with the plastering. On a 4 way switch, do I need to run 3 core or 2 core cable between the switches. Don't want the spark hacking out the new plSter later.

Depends on the method you are using.

Probably three-core these days.

An intermediate switch has four terminals so will at least need four wires, ( two strappers in and two out ) normally bought the switch as two cables of twin and earth,

But it is more convenient to keep the Switched Live together with the strappers so triple and earth is often used

Circuit and cable layouts can be found in the wiki as in this link

//www.diynot.com/wiki/Electrics:Intermediate

In the main four way switches are rotary switches to get the four options. I don't think your really meaning a four way switch. In the main we have on/off and two types of two way switches which we tend to label two way and intermediate.

The standard way to wire is with triple and earth cable but there is a method where we borrow the line from another switch which allows the use of twin and earth. However this method also radiates RF at 50 Hz and messes up any wireless systems from cordless phone to broad band. It's not banned but it is something to be avoided.

So I would always run triple and earth cables between switches even if I could get away with twin and earth.

Transmission lines is a whole module when I did my degree and as you may realise quite complex. The distance between conductors in twin and earth and triple and earth cable is important to prevent losses. When we used power hungry lamps it was not such an issue but with LED lighting getting them to switch off is a real problem. Using the old method of borrowing a line will often cause problems with low power lighting.

There is also the problem were borrowing a line results in what is called borrowing a neutral which is very much outlawed so I would play safe and install triple and earth cable.

Cheers guys,

From what I gather the intermediate just needs linking to the others by means of 2 wires plus the earth obviously, what's the purpose of using the three core

Just looked at the diagram so by using three core one switch will have L1 and L 2 with two wires in each terminal.

Just seen other replies. With DC it does not matter how close feed and return cables are and the school diagram works OK. But with AC if the feed and return don't run together than they will transmit. This is the standard method note the circles showing how the cores are held in the same cable.

As frequency increase so to does the problem and as a radio ham we used 300Ω ribbon cable which held the two conductors as a set distance apart. The same applies with coaxial cable the distance between conductors is very important. 95, 75, or 50Ω coaxial being common sizes.

At 50Hz it's not as big as a problem as with 50MHz but it is still a problem. I once did learn all the formulae to work out the losses but it's not so much the losses as the gains which cause a problem. When your speaker wires pick up the losses they feed these back into the amplifier and then it is re-broadcast as 50Hz mains hum.

Unless you are trained to work out where that hum is coming from is a nightmare. With three switches you have 4 combinations which will cause the lights to light. Likely only one will produce mains hum on Hi-fi, Cord less phone and wireless lan the latter is a real problem as one does not listen to the signal so working out it's the two way lighting causing the problem is really hard.

The two-wire has supply at the first switch and switched live at the last.

The three-wire has both at the first switch, so the switched live has to be returned from the last switch, hence the extra wire which is not connected to the intermediate(s) but passes straight through.

Yeah,

See the reason for the three core now, will put that in ready. Don't realy like the idea of having a single wire just connecting the commons of the two outer switches.

Cheers guys.

Glad you can see the reasoning. To be frank to have reproduced the theory would now be hard for me. My son took most of my books.