Is this permissible?

[hightower]

Had a question in my mind for a while now, thought I'd better ask to see if I can understand better. Please excuse the poorly drawn image below, but hopefully it will help clarify my question.

Let's say some two-way switching like the top half of the image (earths removed in image to make clearer) had a damaged core on the strappers, but the other 2 core (and earth) test fine. Can the setup then be made like the bottom half of the image (so pinch the line off another switch wire at the far end switch (switch 1), use the two good cores of the 3-core as strappers, and then bin the neutral at the near end (switch 2) and just pass the feed to the light using the brown on the 2-core - I think the diagram will show it better than I've just explained it.



It will work (I think!) scientifically, in that the light will come on. But for my learning, is this a good way to solve an issue like this (possibly saving destruction of walls/decor to replace the damaged core), or would it be frowned upon. Furthermore, would it meet regulations - I think the actual circuit is acceptable in a scientific sense (ie feed one switch, 2-core strappers to other switch, feed to light) but can you reuse a damaged cable so long as it tests ok?

I know what best practice would be (new cable etc), but just trying to figure out whether I'm a boy-wonder or a boy-wally!

 

[Billythekid]

It wouldn't be a neutral, it'd be a switched live back to luminaire. In this theoretical scenario would the two lights be on the same circuit? Your thinking has some logic, but I believe you need to give this some more thought. Regards Billy

 

[hightower]

It wouldn't be a neutral, it'd be a switched live back to luminaire. In this theoretical scenario would the two lights be on the same circuit? Your thinking has some logic, but I believe you need to give this some more thought. Regards Billy

I would imagine they'd have to be on the same circuit otherwise it would activate the RCD. I was just referring to the blue core in the twin as neutral for ease, but yes, you are correct - bin the switch live in the twin.

I was just curious more as to how something like this would stand from a regulations stand point.

 

[davesparks]

If it's all on the same circuit then it would be ok from a theoretical point of view and may even get wired with a twin in place of the three core when it's installed.

If they are not all on the same circuit then you cannot do it as you will have created a borrowed neutral (live from one circuit returning via the neutral of another) which is a very dangerous situation.

What you have to consider though is that the cable will still be damaged, and without knowing exactly what that damage is you cannot know how safe it is. The damage may have left the copper of the other conductors exposed

 

[Billythekid]

I would imagine they'd have to be on the same circuit otherwise it would activate the RCD. I was just referring to the blue core in the twin as neutral for ease, but yes, you are correct - bin the switch live in the twin.

I was just curious more as to how something like this would stand from a regulations stand point.

What will now control this 2nd light?
How will you achieve switching at both lights?

 

[hightower]

So the answer seems to be the scientific theory is sound, but we'd expect installs like this to be done by cowboys - sound about right?

If a client said they had this fault, would you do it as per the lower half (re-use the 'good' cores) provided everything else checks out (on the same circuit, the 'good' cores test perfect etc) or would you tell them you'd only do the work by dropping in a new cable?

 

[hightower]

Couple of clearer images in case my first diagram didn't make much sense (yes, I am a photoshop master)

 

[davesparks]

So the answer seems to be the scientific theory is sound, but we'd expect installs like this to be done by cowboys - sound about right?

If a client said they had this fault, would you do it as per the lower half (re-use the 'good' cores) provided everything else checks out (on the same circuit, the 'good' cores test perfect etc) or would you tell them you'd only do the work by dropping in a new cable?

As I said before, without knowing exactly what damage has happened to the cable you do not know what condition it is in. If the damage has left the insulation of the other cores damaged you could be leaving live parts exposed which a slight bit of movement could cause to make contact with earth and start a fire.

 

[hightower]

As I said before, without knowing exactly what damage has happened to the cable you do not know what condition it is in. If the damage has left the insulation of the other cores damaged you could be leaving live parts exposed which a slight bit of movement could cause to make contact with earth and start a fire.

Totally, thanks for your help

 

[conrad]

I would imagine they'd have to be on the same circuit otherwise it would activate the RCD. I was just referring to the blue core in the twin as neutral for ease, but yes, you are correct - bin the switch live in the twin.

I was just curious more as to how something like this would stand from a regulations stand point.

Obviously need to change the connection in the light changing the feed to a switch.

 

[Midwest]

hightower, you've asked two questions on 2 way switching in two different threads. I see from your occupation, that you are an IT manager. There is a DIY section in this forum, that unqualified persons can post in and be advised by certain forum members. Might be better that you ask the mods to allow you entry into that section.

 

[GMES]

hightower, you've asked two questions on 2 way switching in two different threads. I see from your occupation, that you are an IT manager. There is a DIY section in this forum, that unqualified persons can post in and be advised by certain forum members. Might be better that you ask the mods to allow you entry into that section.

High tower is a Trainee and part of the trainee section, hence the title under his username, so it won't go into diy, the trainees keep most of their questions in the ts but are also allowed to ask questions in the main forum.

 

[Midwest]

High tower is a Trainee and part of the trainee section, hence the title under his username, so it won't go into diy, the trainees keep most of their questions in the ts but are also allowed to ask questions in the main forum.

Ok, I'll keep my nose out then!

 

[GMES]

Ok, I'll keep my nose out then!

I didn't tell you to keep your nose out, I merely pointed out that he was a trainee and therefore gets cut some slack, and why would we ever put a trainee question in the diy forum.

 

[Midwest]

I didn't tell you to keep your nose out, I merely pointed out that he was a trainee and therefore gets cut some slack, and why would we ever put a trainee question in the diy forum.

As per my reply to your PM, should leave these matters to the mods (that's what I meant), and no offence taken.