lost landing light

[ezekiel]

after installing a split rcd board and on reinstating the circuits, the landing light switch at top of stairs is fine however the two gang at bottom of stairs which did work landing and livingroom now both switches will only work living room.

any ideas as to reason (im guessing that since neutrals have now been split at db this may be the issue but not sure)

 

[Spark123]

Are you sure it worked before? Changing a CU shouldn't have any effect on the operation of the switches unless something more sinister was going on - a borrowed neutral when you end up with the line conductors on 2 separate RCDs will cause it the RCDs to trip. Have you disturbed something whilst testing? The only other logical explanation I can think of would be if the line and neutral were somehow reversed beforehand on one of the circuits? - I haven't thought this through yet fully!
Odd that it works with one switch and not the other.

 

[ezekiel]

thanks sparks, it actually not my job, just one i came across today at work with a one week wonder course builder i work with occasionaly as ive heard about borrowed neutrals wondererd if this was the cause and how you would:
a. identify borrowed neut
b. fix problem

 

[Spark123]

Are the RCDs tripping when the light is operating, or were they before someone messed around with the wires? If it is a borrowed neutral then the best way imo is to pull in the required 3c&e between the up and down switches and pull in 2c&e from up switch to light and wire it properly.

 

[ericmark]

Years ago it was common to use two core as strappers between two way lights borrowing a line from another light (Referred to as borrowed neutral) one cure when fitting RCD's is to remove two way lighting function.
Since you said you did not do the job I would consider this likely.

Two ways to fix
1) Replace with 3 core and earth strapper.
2) Run both upstairs and downstairs lights off same MCB/RCBO.

The latter may need addition of emergency lighting to comply with regulations.

 

[ezekiel]

as far as im aware they were fine till the board was swapped when he xxplained i was trying to draw it out to see if i could work it out but not getting it.

in borrowing a line would you run a single core to where its needed?

 

[Spark123]

If it was borrowed then there could have been a link between the living rm perm live and the com for the down landing light switch. 2c & e from the L1&L2 of the down landing light switch to the L1&L2 of the up landing light switch. Com from the up switch would go to the landing light, making up the top schematic for 2 way switching here:

Imo the best way to retain 2 way switching would be to convert it to the bottom diagram utilising a 3c&e between the two switches.

 

[Taylortwocities]

in borrowing a line would you run a single core to where its needed?

Not unless you want to run it in conduit. You cant run single insulated singles around the place you'll need a cpc too. May as well run regular twin & earth.