2 way light circuits - is this crazy?

[fumb]

Hi there,

I'm planning a light circuit rewire as my vintage 60s circuit is a cpc free zone
I am as yet uncertain whether I will get this done via a friends company (which is NAPIT "registered" and hence able to self-certify through their scheme) or whether I will go through the LBC route and get it signed off that way. I do have access to all the equipment required to test it myself though unless I need IR testing at greater than 10KV or circuit resistance to less than 0.01ohm

Anyhoo, I would like to use 1.5mm 3 core and earth instead of twin and earth. This means I can run point to point round the switches and ceiling roses with a single cable carrying live, neutral, switched and cpc and I have live and neutral in all the backboxes so I'm future proof for fancy dimmers etc. I've run this past my friend and so far he believes this is in compliance with regs although I'm not 100% sure he's certain. I don't see it as much different to looped neutrals in the back of the switch and don't see any issues with it

So then I came up with another idea to run 2 way switched circuits which seems to have thrown him for a loop. I think it's possible to do this using 3core+e maintaining the point to point power loop

Any feedback muchly appreciated, especially regarding what regulations this might contravene

Here's what I have in mind. The top circuit is the normal way, two linked 2 way switches.
My idea is below. Rather than feeding the switched pair to the second switch and returning the common as it were why not use the bottom circuit with the light fitting seving as a middle junction box. That way I get to continue the L and N wires into the next switch location so I can maintain my ring. The bulb will either be switched between L & N (making light lol) L & L or N & N, both of which make light not work

I hope this makes some sort of sense. It would appear to be a little too far out of the box thinking to have any kind of direct regulation
I know it will work though

PS, I also know it won't work for 3+ way switching

 

[Lectrician]

Sounds OK except for the 2way - you would need 4 core and earth for this.

Are you looping in and out of pendents and a drop the switch? OR looping from pendent to switch to pendent to switch to switch to pendent etc? This may make things rather confusing.

 

[bernardgreen]

This works but there are two serious problem with it

[1] when the light is OFF both side can be live. Changing a bulb is then quite danagerous.

[2] The switches need to be a type that quarantees a 3 mm break before make action other wise the live and neutral can be shorted as the moving contact inside the switch moves from one pole to the other.

An arc can be formed that keeps burning until the fuse blows or the switch burns out

With incandescent lamps you may get away with it but definately not recoomended. I have changed a few switches which have gone "pop" and blown the fuse or MCB

 

[Spark123]

It also contravenes the regulation about having single pole switches in the phase conductor only.

 

[ColJack]

it will work with a modification..

connect the lamp between swithed live and neutral at the light.. this then acts like 1 way switching but from 2 points.. ( eg you have a live and a swithched live at one switch, then loop both into the next switch and then on to the light.. )

and this way you can add more light switches.. just use 1 ways..


your way is a no-no, since you are switching the neutral as said and there is the posibility of L/N shorts inside the switch..

I would however not bother with 3C+E to use as a feed cable..

just stick with T+E to run the mains round and link with 3C+E where you need to link lights,

run 3C+E to each switch if you absolutely must but ensure you sleeve the black with blue and the grey with brown to denote that the black is neutral..

This last will no doubt spark a debate over what core to use as what, since it's not written in stone anywhere.. just personal prefference..

I used to use...

RED = LIVE
YELLOW = SWITCH ( sleeved red o/c )
BLUE = NEUTRAL ( sleeved black.. )

since blue was neutral on flex...

I now use

BROWN = LIVE
GREY = SWITCH ( sleeved brown )
BLACK = NEUTRAL ( sleeved blue )

since black WAS neutral.....

 

[fumb]

So, long story short yes it's crazy and yes it contravenes the rules

I must admit the short thing never occurred to me since I assume switches would always be break before make

Oh well, idea dead and buried

Looks like I'll be ending up with 3c&E from switch to pendant for power and switched and t&e from pendant to next for just power with the odd extra cable for 2 ways

Many thanks for the input, even if you did sink my battleship

I shall now retire back to the bunker and await the outcome of the great cable colour debate

 

[fumb]

Actually, one last question if I may

Should this have been blindingly obvious to a genuine spark?

I'm slightly worried that my friend didn't spot it unless he was just trying to humour the idiot

 

[ColJack]

actually, it's permanent live and neutral from light to light, not switched...

it can still be done the way I said... not sunk completely, just kind of flooded a bit... just need help to bail it out...

and yes it should have been obvious to a good sparky..
but i must admit i still get switching questions from the guys at work who have been "factory bound" for the last decade or so.. seems if you don't use it you lose it...

 

[fumb]

Oh well,

I have a suspicion he was just trying to keep me quiet. I hope so since he's been on the tools since we left school 20 years ago.

I think I'll just stick to tried and tested methods. Probably the sensible thing to do with electrics


Ta muchly for the advice

Right, to the lifeboats. Women, children and idiots first

 

[sm1thson]

An arc can be formed that keeps burning until the fuse blows or the switch burns out

like this

 

[RF Lighting]

this is still my favorite

 

[TicklyT]

I saw a 2- way setup switching between phase and neutral. The DIY'er who put it together was pleased he had saved himself a few pennies on cable, and wondered why everybody didn't wire 2 way switches that way.

He eventually gave up and rewired it correctly when he got fed up with re-setting the MCB every time he used a switch, and changing the burnt out switches weekly. The final straw was when he threw himself off the top of his steps when changing a lamp, having forgotten that both connections could be live when the lamp was off

His day job?..... Designing and installing electrical installations on aircraft

 

[bernardgreen]

His day job?..... Designing and installing electrical installations on aircraft

Ironically on aircraft it is acceptable to do things like this where using a more complex switch will reduce the number of conductors in the loom and thus reduce weight.

 

[Adam_151]

One way that seems to make a lot of sense to me is to loop through the switches instead of the lights and take a switched phase and a neutral upto the lights from the switch.

In two way switching, take a 3c+cpc across to the other switch carrying two strappers and a neutral, and then take a switched phase and neutral upto the light from there. If you are careful with which cores you use as your strappers and pick cores that are on opposite sides of cpc then you'll limit capacitive coupling between the two and minmise the chances of the flashing CFL problem (it does havever mean you have to deviate from the accepted way of re-sleeving the cores in 3c, but as long as you re-sleeve properly then its not much of an issue)

 

[fumb]

His day job?..... Designing and installing electrical installations on aircraft

Ironically on aircraft it is acceptable to do things like this where using a more complex switch will reduce the number of conductors in the loom and thus reduce weight.

How bizarre that should come up

There's a reason why I know this works just fine

Great, or perhaps not, minds think alike