2-way lighting circuit

Its there in the text. the latter means it becomes too easy to take a neutral from a different circuit to the one that supplies the live.

This is colloquially referred to as a "borrowed" neutral.

Using the 1st reduces the risk of borrowed neutrals.

(A fully populated RCBO CU will in fact detect borrowed neutrals but MCBS won't. On a twin RCD split load, it depends on whether the borrowed neutral cones form the same RCD as the live or from the other RCD. The former won;t trip but the latter will.

I thought that they explained it fairly well.

In domestic premises you tend to get such a configuration on the stairs and if the live feeds at top and bottom of the stairs are on different lighting circuits as is actually quite common (or at least was back in the incandescent lamp era).

I found a nasty one in my home when I moved in. Strictly the oil boiler heating engineer found it when replacing the pump. Someone had provided a sneaky way of powering the CH pump from a switch on the lighting circuit from the living room. IOW the CH circuits were not safe to work on because it was stealing power from the downstairs lighting circuit.

Thank heavens for neon screwdrivers!

It depends. If you only have one lighting circuit then it is simple but if you have more than one things could be dangerous and still live.

My hall and landing lights are fed from the upstairs lighting circuit. This has advantages, such as the time I arrived home in the early hours of the morning, switched the light on and the bulb blew, tripping the MCB - it meant that the downstairs circuit had not tripped and pushing the kitchen door open, allowed me to use that light to see the burglar alarm buttons and cancel it in time, so avoiding waking all the neighbours up!

My hall light is on d/stairs RCBO and the landing light is on the Upstairs RCBO.

Both the hall and landing switches are in a 2 gang switch plate at all doors. So if one circuit trips, i simply turn the other light on and there is usually enough light for most people to then work with.

It also says that it's fine when executed correctly.

I'm thinking another problem with the 2-wire control is that there is T+E from the ceiling rose to the 1st switch, then 3+E cable between the switches (of which one core is the switched live). The switched live will have to find its way back to the ceiling rose via the T+E, which will require a junction.

Not the case actually.

One method is:

you use the 3 core to wire the two way switches together so common to common, L1 to L1, L2 to L2 and earth the back boxes together.

Then your Twin and Earth wire from teh ceiling rose is then wired across L1 and L2 in one of the switches and teh earth added to the back box.

Another method is put one wire from ceiling rose switch cable into common terminal of 1st switch.

Then 3 & E cable is used to wire L1 to L1, L2 to L2 and then use the third remaining conductor to connect to Common of the remote switch and then to the other wire coming from the ceiling rose at the first switch via an insulated choc block connector.

Yes, that's what that web-site calls 3 wire control.

And that seems to be the 2 wire control.

The risk of connecting the live from one circuit to the neutral of another, which is both dangerous, and also incompatible with RCDs in some cases.

It it also more likely to cause interference for inductive loop hearing aid users.

Here is the preferred option:

The light and switch wiring are as per normal, and you run one 3&E between the switches.

Why, I'd have thought the difference was minimal. Brian

That much depends on how much you like being electrocuted!

Borrowed neutrals are a serious electrical faults, not just a minor problem that trips RCDs.

If you isolate a circuit to work on it, it can be very unwelcome to find that its neutral is now live because it it connected to the live on another circuit via a lamp.

Take a look at this ..... big changes now in how things can be done.