Different way to do two way lighting

[Ian Mills]

Came across a odd system today here in a house in France, thought I would share it with you all,
light switch down stairs live to one output of the switch neutral to other then what would normally be input went up to the light, upstairs switch same set up,the two wires from the switches connected to light , if you turned down stairs switch to live and upstairs to neutral light came on , change downstairs switch to neutral you have 2 neutrals at light so goes out, turn up stairs to live you have 2 lives at light so light goes out, change any switch again and comes back on so has worked for maybe 35 years, I do not know how many people working on the lights have been killed over the years, had to stop and draw it out to see what was happening

 

[pc1966]

That seems to combine all of the worst possibilities that a working two-way switch arrangement could have!

As a complete aside: where I have seen a similar arrangement is for DC motor control when you have two change-over relays (one allows forward motion, the other reverse) with the moving contacts of each relay to the motor, and the fixed N/O and N/C relay contacts going to positive and negative/ground supplies. They key point of that sort of switching arrangement in the DC motor case is it shorts out the motor when "off" so the motor stops very quickly, and operating both forward & reverse relays simultanbeously is safe as that is also "off" (motor shorted, but both at +V).
[automerge]1595627739[/automerge]
Basically a mechanical H-bridge driver!

 

[jackhammerJIM]

I worked on a big house in the south of france all the 2 / 3 ways were switched through contactors .

 

[Lucien Nunes]

This 2-way configuration was called the 'Carter' system, used in the early decades of the 20th century but soon fell out of favour and became increasingly non-compliant in most places as regs evolved.

Making both terminals of a lamp live to turn it off seems ridiculous here and now, but if you consider older delta-derived single-phase systems where there is no neutral and one lamp wire is always live, the extra risk posed by the Carter system is not great, concerning mainly the polarity of a screw lampholder. I do wonder whether there were cases of crossfire at the switches, where the normal momentary arc in series with the load as the circuit breaks, diverts to a full-on power arc between the L & N contacts. DC-rated QMB and tumbler switches would have been much less likely to do this than AC micro-break types though.

Another interesting thought about Carter 2-way is when it is combined with single-core earthed-concentric wiring. With EC, the neutral is everywhere - it's the cable sheath - so most jobs can be done with single-core cable. For lighting, loop at the switches; one single-core feed, another for the loop out and another to the light. For Carter 2-way, L & N are already present at both switches; all that is required is one extra single-core cable from the second switch to the light. A remarkable economy of material.

I remember a eureka moment when I was young, while examining the electric window switches in the car. I knew how to reverse a PM motor and about dynamic braking by closing the motor circuit onto itself at rest. The switch made both motor wires normally negative; pushing the switch up changed one side to positive, down changed the other side. What puzzled me was that the switches had two separate negative terminals linked with a wire at the connector. The penny dropped when I realised that although our car (a Citroen CX) only had one switch per window, by connecting the N/C contacts of each direction separately to the outputs of an identical switch instead of to negative, they can be daisy-chained to give control from multple positions.

And intermediates work with Carter, too.

 

[Ian Mills]

This 2-way configuration was called the 'Carter' system, used in the early decades of the 20th century but soon fell out of favour and became increasingly non-compliant in most places as regs evolved.

Making both terminals of a lamp live to turn it off seems ridiculous here and now, but if you consider older delta-derived single-phase systems where there is no neutral and one lamp wire is always live, the extra risk posed by the Carter system is not great, concerning mainly the polarity of a screw lampholder. I do wonder whether there were cases of crossfire at the switches, where the normal momentary arc in series with the load as the circuit breaks, diverts to a full-on power arc between the L & N contacts. DC-rated QMB and tumbler switches would have been much less likely to do this than AC micro-break types though.

Another interesting thought about Carter 2-way is when it is combined with single-core earthed-concentric wiring. With EC, the neutral is everywhere - it's the cable sheath - so most jobs can be done with single-core cable. For lighting, loop at the switches; one single-core feed, another for the loop out and another to the light. For Carter 2-way, L & N are already present at both switches; all that is required is one extra single-core cable from the second switch to the light. A remarkable economy of material.

I remember a eureka moment when I was young, while examining the electric window switches in the car. I knew how to reverse a PM motor and about dynamic braking by closing the motor circuit onto itself at rest. The switch made both motor wires normally negative; pushing the switch up changed one side to positive, down changed the other side. What puzzled me was that the switches had two separate negative terminals linked with a wire at the connector. The penny dropped when I realised that although our car (a Citroen CX) only had one switch per window, by connecting the N/C contacts of each direction separately to the outputs of an identical switch instead of to negative, they can be daisy-chained to give control from multple positions.

And intermediates work with Carter, too.

This system would have gone back to when electric first arrived in this region the system was very simple it would have been 3 phase 15A per phase, there where no fuse boxes, EDF supplied a 500ma 15A trip, cables went direct from this around the house with a fuse built into every light switch and socket, if the total load got more than 15A it would trip, normally not very quickly, over the years the power has being increase and now is 30A per phase, DIY people have taken out some of the fused sockets and light switches replacing them with new un-fused modern units leaving only the 30A main trip to deal with any problems.
Normally I would rip the lot out and start again but some people have not got or do not want to spend the money,
In this case I fitted a 30ma 3 phase rccb and 3x 16A trips used as a combined lighting socket circuit, not ideal but does give a exceptable level of protection, cable all pvc covered and in okay condition.
I found the washing machine, dishwasher and fridge along with half the sockets in the house all on 1 phase, so cable would have being overloaded.
I need to go back and fit new supply to both washing machine and dishwasher, I already had put a new supply to one part of the installation as it had a earth fault that was taking the trip out;
I have also added 2 new consumer units for other work they are doing and sorted out another that had been in about 25 years
I think at the end of the day cost will not be much less than a rewire, but the customer is always or nearly always right
PS thanks for the info on the carter system great to know its name

 

[stevethesparks]

Came across a odd system today here in a house in France, thought I would share it with you all,
light switch down stairs live to one output of the switch neutral to other then what would normally be input went up to the light, upstairs switch same set up,the two wires from the switches connected to light , if you turned down stairs switch to live and upstairs to neutral light came on , change downstairs switch to neutral you have 2 neutrals at light so goes out, turn up stairs to live you have 2 lives at light so light goes out, change any switch again and comes back on so has worked for maybe 35 years, I do not know how many people working on the lights have been killed over the years, had to stop and draw it out to see what was happening

So in one instance at the pendant, the brown and blue will be correct polarity, in the second instance they will be wrong polarity.
Sound european to me

 

[Ian Mills]

So in one instance at the pendant, the brown and blue will be correct polarity, in the second instance they will be wrong polarity.
Sound european to me

even the sockets can be wired both ways legrand do a double socket where the two are wire one live on left one live on right problem is things like boilers with a fuse built in the fuse has a 50 / 50 chance of being in neutral helps to keep you awake