Separate lighting circuits/borrowed neutrals

[JohnW2]

Although it basically used the 'old' method of 2-way switch wiring, it used 3C+E cable, with the L feed travelling in the third core, with the two strappers. ... so there are variations around.

That would be the modern (conversion) method and surely not involve a borrowed neutral, wouldn't it? ... Edit - or rather a miswired conversion method.

As I said, what I inherited was a 'variant'. It certainly did not involve a borrowed neutral, which I imagine is probably why it was done.

It was not quite the 'modern method', since, with that, the third core (the other two being the strappers joining the two L1s and the two L2s) would be joining the two COMs. With mine, it was simply a permanent live feed to the COM of switch remote from the light - hence representing a 'correct circuit' source of the L, rather than a 'different floor L' which could/would have been the case in the absence of the third core.

Functionally, there was absolutely nothing wrong with what I had, and it did not involve the potential problem (EM radiation etc.) of an 'unaccompanied conductor'.

Kind Regards, John

 

[JohnW2]

It all boils down to a risk assessment my house with two rather old RCD's fitted in the early 1990's has a RCD trip on average 6 times a year my mothers house with all RCBO's in kitchen has never had one trip.

Experiences vary a lot. I have been living with about 10 RCDs for 15-20 years (so some are fairly old), and I don't think I've ever experienced an 'unexplained nuisance trip' - what few trips there have been have, IIRC, all been 'for good reason'.

Kind Regards, John

 

[Risteard]

5) It is permissible to go up to 16A for lighting as long as there are no items like ceiling roses which are only rated at 5 amp.

Rubbish. You aren't going to exceed 5A load on a ceiling rose! 16A is permitted for such accessories, as stated explicitly in BS 7671.

 

[ericmark]

5) It is permissible to go up to 16A for lighting as long as there are no items like ceiling roses which are only rated at 5 amp.

Rubbish. You aren't going to exceed 5A load on a ceiling rose! 16A is permitted for such accessories, as stated explicitly in BS 7671.

Since a bulb should have a built in fuse having a BA22d bulb holder rated at 2A is not a problem and where the supply is feed from switch to switch with 20A rated switches having a ceiling rose rated at 5A again is not a problem.

I personally would consider a ceiling rose would take well over 5A, but where the ceiling rose is being used as a junction box, which was the standard method until we started using down lighters, then when rated at 5A that becomes the maximum rated capacity for the circuit, the 3 meter rules comes in, and so where the next lamp in the circuit is over 3 meters from the junction box or ceiling rose rated at 5A then the maximum size of fuse or MCB is also 5A.

Using common sense a 6A MCB is clearly good enough and we don't have to hunt out a 5A MCB but to double or triple the rating to 10 or 16 amp is clearly going OTT.

If the lighting circuit with standard bulbs exceeds 6A then that would mean where ceiling roses are used as junction boxes you need to split the circuits, swapping the 6A MCB for a 10A MCB is not an option.

Personally because of the problem when bulbs blow the high current due to ionisation of the gases in the bulb and possible welding of bulb contacts as a result even if there are no junction boxes below 16A rating fitting 10 or 16 amp MCB's or even using C rated instead of B rated is likely to mean the whole bulb holder needs changing rather than just the bulb and also more likely to take out any dimming switches used so even if the rules did not say use a 6A MCB to me using a 6A B rated MCB for lights is the sensible way to do it.

Today there is not really a problem with all lights from a 6A B rated MCB we have with the so called energy saving bulb reduced the demand on the lighting circuit.

 

[securespark]

If there is a borrowed neutral, I would feed a neutral from the ground floor lighting to the landing light.

This has the added bonus that if the upstairs lights go off, the landing light remains on.

 

[AndyPRK]

If there is a borrowed neutral, I would feed a neutral from the ground floor lighting to the landing light.

This has the added bonus that if the upstairs lights go off, the landing light remains on.

But the disadvantage of having no light at all on the stairs from either landing or hall light if that circuit goes off

 

[ban-all-sheds]

True, but most people have rooms upstairs where they can turn on lights and open doors, and get enough light that way to see to get downstairs.

Or use a maintained or sustained fitting for the landing light.

 

[ban-all-sheds]

... the 3 meter rules comes in, and so where the next lamp in the circuit is over 3 meters from the junction box or ceiling rose rated at 5A then the maximum size of fuse or MCB is also 5A.

Err... umm... "3m rule"?