needles and haystacks

[Markey]

i know this is going to be a bit difficult to answer but

i noticed that neither the upstairs or downstairs mcb for the lights would actually switch off the lights on their own, so i worked out the most likely cross was on the stairs and indeed someone had installed a single gange single way switch where there used to be a two gang two way switch, so i have replace that and it all now works correctly.

One thing that i did notice is there is a single red cable (single as in not part of a T&E cable) into a choc block behind the switch. Does this mean i have not correctly undone their mistake or its there for some other reason and if thats the case would anyone like to offer an opinion on what its for?

 

[ericmark]

Years ago two way switches on stairs would normally have a two core and earth cable between the two switches one switch plate would be a double and the line from non two way switch would be linked across to two way switch.

First problem was mains hum on radios etc. because the line and neutral did not follow same path.

Second both switches had to be supplied from the same MCB which would mean both upstairs and downstairs lights had to be from same MCB.

As time went on it became the norm to use a different MCB for upstairs and downstairs and all to use 3 core and earth between the two switches.

When houses have been updated sometimes the fact that this old method of wiring two way switches has been used is overlooked.

In last year this has caused problems as separate RCD's are fitted to upstairs and downstairs.

When these problems are high lighted those working on the electrics have to find a way around the problem. These do not always follow standard wiring practices.

I will guess something like this has happened to your house and is underlying problem causing what you have found.

 

[Click-Sure]

Theres a whole estate near me that has a needless interconnection between downstairs and upstairs lighting circuit at the bottom of the stairs. Dead tests revealed it before I got to the point of watching RCD's trip!