The question seemed perfectly reasonable since there are a variety of ways - some more common than others - used for these two way switching arrangements.
I would have thought from the nature of the question that would have been obvious.
Moot point since no qualifications are required to replace a light fitting.
You seem to be jumping to conclusions here.
You also need to learn that asking questions is not a sign of inadequacy or weakness.
The real question is, having found such a wiring case can he fix it legally? Its not legal to leave it in a dangerous condition and it would appear to be in a dangerous condition. Even if its not dangerous to the occupier its still not legal to leave it if its dangerous to for example, another handyman.
Not really - even wiring to the 17th edition using the "standard" arrangement with 3&E run between floors to facilitate the "other" two way switch, you will still have a switch position containing live wires from two separate circuits.
If it were truly dangerous, then yes one would either have to refuse to do the work, or only agree if one were also allowed to rectify the cause of the danger (or find an alternative workaround). However this is not necessarily one of those situations. If working on a switch that is known to switch lamps notionally covered by two different circuits, then its a fair assumption that you may need to isolate both circuits to make it safe to work on.
Cases with borrowed neutrals are certainly examples of poor practice - but again its fairly common poor practice!
Why? You have live running to the top switch, two switched lives from the top switch to the bottom switch and one switched live running back to the fitting, only one live circuit is needed and no neutrals run down the cable at all. Operating the switches will either turn the light on and off if the wrong circuit is isolated or do nothing.
Well they are done by electricians and they aren't all the brightest of people. ;-)
And that means the bottom two gang light switch has lives from the upstairs and downstairs circuits. (and the upstairs likewise if two way switching is implemented in both directions).
Well while statistics and experience would support this view, there are also some fairly smart ones about.
Perhaps he cannot legally resolve the problem, so what he should do is flag up the problem to the owner of the property and let them then employ someone suitably qualified to resolve it.
I've never come across that arrangement. It would appear to me to be a dangerous practice to have an upstairs light on a circuit marked 'downstairs'
I would expect the hall light to be on the downstairs light circuit and the landing light to be on the upstairs cisuit. That way, if one circuit fails, you still have light in the stairwell, which is one of the most dangerous places in a house not to have any light. I also have an emergency light above the stairs, in case of a total power failure.
It's true that there's only one neutral connected but it's connected to the wrong circuit. Looking at the diagram, the neutral return (from the upstairs light) should have been taken back to the neutral of the downstairs circuit. As you say, this should have been done using three core and earth but whoever did the installation obviously didn't have the correct cable. He could have used an extra single core cable to make the return to the downstairs circuit but chose to use a much shorter run to tap into (i.e. 'borrow') the neutral of the upstairs circuit.
It's clear that the name, 'borrowed neutral' is recognised by professionals in the field and it's equally clear that the arrangement is widely used despite being frowned upon. The whole situation should serve as a reminder to us all to check every wire individually before doing any related work.
As far as the two live wires are concerned they're both off one circuit (downstairs in the drawing) but they're both switched - only one is live at any time - so not causing any problem provided that the circuit is switched off at the CU.
The neutral used for that section of circuit in the diagram supplied by the downstairs circuit, is the neutral intended for the upstairs circuit - it is therefore 'borrowed'. I agree that if the live for the upstairs circuit were used, that there would not be a problem.
I have three lighting circuits covering three floors. All multi way switched. On the first floor I have three circuits on one plate. If one circuit should trip, there will be enough spill from another to see your way out.
Only a fool assumes a circuit is dead without checking before working on it in a place strange to them. What seems logical to one may not to another. Another example here is the light inside the cellar door where the CU is. That isn't on the ground floor circuit for good reason. The CU is clearly and accurately labelled, though.
The live must come from the same circuit that the neutral returns two. This normally means that the light on each storey will connect to the neutral belonging to the circuit feeding that storey, hence the live needs to come from there also.
I have drawn an example of double two way switching using the 17th (and
16th for that matter) edition recommended way of wiring two way switches here:
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borrowed neutrals (so RCBO safe), feed to each lamp from the adjacent circuit for the storey, but two circuits live conductors present at each two gang switch.
Does this mean that RCBOs on the two circuits connected by a borrowed neutral will be ineffective? Would there be any direct danger in putting RCBOs into such an arrangement?
If so, is removing the borrowed neutral the only remedy?
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