2 way 2 gang switches

seosamh

I recently got an attic conversion but the switches that control the lights as you make your way up from the ground floor are not working as they should. Sometimes the light for the landing in the attic cannot be controlled by the light switch from the floor below because of the relative switching of the ground floor and second floor 2 gang switches. Other times it works fine. It is funny that the switch in the hall impacts the attic switch.
Is this sort of problem a DIY kind of thing to solve, I am not afraid to have a go. Or should I get a professional?
Thanks.

Diggerdunne

It sounds like the electrician took a feed off a strapper so the lights in the attic are dependent on the landing light strapper position. Not good practice. Ya can open the switch and hope the switch feed and not the switch wire is behind the switch. If the feed is there then you just need to loop off it to your new switch....

seosamh

Would that explain how having gotten to the second floor it may be necessary sometimes to return to the hall to change the switch ON/OFF position for the stairs light so that the attic light can then be controlled from the second floor and of course the attic?

The second floor has a 2 gang 2 switch to control the stairs light and the attic light.
The hall has a 2 gang 2 switch to control a light in the hall and the stairs light
The attic has a 2 gang 2 switch to control the attic light and a bathroom light.

Bruthal

Yes that would be one thing that would explain it. Another is a possible mix up between a strapper and a switch wire/feed.

This would also mean one switch (hall one) would need to be in one position for the others to work, as would using a strapper as a feed from a switch that had no switch feed like d-dunne suggests.

It could be very confusing for a diy person to have a look, but straight forward for a competent electrician.

seosamh

Diggerdunne wrote: »

It sounds like the electrician took a feed off a strapper so the lights in the attic are dependent on the landing light strapper position. Not good practice. Ya can open the switch and hope the switch feed and not the switch wire is behind the switch. If the feed is there then you just need to loop off it to your new switch....

Yes from looking at it today, he did take a feed from the strapper. And the two wires for the switch - are they strappers or does one go to the light. How can I tell?

Strangely, when I used a phase tester to check the wires for the switch in the hall, it lit up brightly for one wire (the one the switch connected to the common) but the other wire the tester lit faintly. I found this strange as I flicked the switch there was always this faint light for the wire not 'switched' to the common. What could cause this?

Bruthal

seosamh wrote: »

Strangely, when I used a phase tester to check the wires for the switch in the hall, it lit up brightly for one wire (the one the switch connected to the common) but the other wire the tester lit faintly. I found this strange as I flicked the switch there was always this faint light for the wire not 'switched' to the common. What could cause this?

This is caused by induction from the live strapper to the disconnected strapper. It is enough to light a phase tester faintly.

Marcus_Crassus

There's a lesson in there somewhere -- never trust a phase tester!! I was taught to never use them while in Fas, and on the job!

Bruthal

Well a bit more intuition is useful rather than just saying never trust a phase tester because fas said it. I remember hearing that one myself a long time ago. It is not giving false information really, it is showing a low glow on a conductor due to induction. They can be handy for indication purposes, but dont show magnitude. Rarely use them myself though.

Get a digital multimeter in the same situation. Test from live to neutral at the ceiling rose on a landing light while the 2 way setup has the light off, and bulb out, I seen them show 40 or 50 volts, which is there, but only with the incredibly small load of a multi megaohm digital voltmeter. Connect anything at all across this, for example, re fit the bulb, and this reading will become zero. The voltage will still show with CFL`s in the bulb holder though, as thier impedence is even higher than a digital multimeter when they are not lighting.

Its for the same reason the phase tester will show a dim glow rather than no indication, the circuit through it and the user, floor etc, is of very high impedence.

So a digital voltmeter can also give misleading readings, but it is giving correct readings for something of its impedence in a circuit, such as in the 2 way ceiling rose test mentioned above. A person touching the 2 points changes the circuit as a persons impedence is far lower than a multimeter.

So if a 1 megohm resistor is connected to a live terminal, and the multimeter tests from the other side of the resistor to neutral, it will show close to the mains voltage. If a person now touches the same 2 points, the voltage will almost all be across the 1 meg resistor, and near 0v across the person.

We know the above is not an every day occurance, but if a digital multimeter is used to test between a live and an earth wire from a shower unit for example, and the earth is connected to nothing at the mcb board, the reading can still show a high percentage of the 230v supply voltage, which is misleading, althoug correct for the situation.

The esb used to use a set of testers that had a solenoid moving indicator in them for 400/230v, which was relatively low impedence compared to digital meters, because they were more positive than high impedence testers, Not sure what they use these days. They were handy for tripping RCD`s from a socket:D

After all that, id agree phase teaters are not a great test method, just an indicator.