One of the switches in this 2 way setup has been acting up, I popped it off to replace it and it's wired like this:

wires entering the rear of the switch

The only configuration I know of that is like this is the Carter system. Is this definitely Carter or could it be something else? If it is Carter then how bad is that, does it need rewiring?

Here's a shot of the wires entering the wall, in case that helps:

wires entering the wall

  • the yellow one is the ground. looks like the bottom 2 reds are one set. and the blue and red is another set. not sure. so i am adding a comment
    – Harsha M V
    Mar 6, 2011 at 19:11
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    I can't answer your question without putting a voltmeter to positively identify the travelers, hot, and load conductors. not familiar with the UK color codes. The Carter system has been outlawed here in the US since 1923 as it puts hot on the shell casing of light sockets. Take a look at this link and back engineer which system you have. Really good diagrams and explainations. en.wikipedia.org/wiki/Carter_system Mar 6, 2011 at 19:48
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    Solid yellow is not (and never has been) ground in the UK, ground is green/yellow. Red used to be live, blue is now neutral but used to be L3, yellow used to be L2. I back engineered from Wikipedia already, Carter is the only one it could be based on how many wires are going where.
    – ZoFreX
    Mar 6, 2011 at 20:12
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    It looks like they've used a four core (the red, yellow, blue + earth wire) and a 3 core but the black from 3 core has been resheathed in red (possibly to indicate it's live). Can you give more detail on the "acting up" bit.
    – ChrisF
    Mar 6, 2011 at 20:18
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    Looks like the images aren't displaying any longer.
    – Tim Post
    Jun 26, 2011 at 14:51

2 Answers 2


The only dangerous thing i see there is that that the wires is not properly inside the plug..

If you see the copper on the red wire = dangerous.

But the flicker will be because it is not screwed in properly most properly. You will need to turn off all power and look properly on the wires.. you will need to pull them .. like pulling a door to open is enough.. if wire comes out then that is the flicker problem.

Your plug should look like this with the wires... and the screws should be tight.. You see the wires are inside the holes and you cannot see any bare wire! The bare wire must only be enough for the screws to touch.. sometimes people fold it over for better contact.

enter image description here

  • Thanks, I already re-stripped and screwed in the wires which did indeed fix the flickering problem. I already knew the exposed copper was bad, but thanks for the very clear diagram, I'm sure that'll be helpful for others finding this :) I still think it's the Carter system btw, but without a live tester of some sort I can't really test that theory.
    – ZoFreX
    Jul 5, 2011 at 14:08
  • I'm accepting this one as re-doing the wires did fix the actual problem at hand, and as I am no longer at this property I can't test any of the theories on the wiring.
    – ZoFreX
    Apr 11, 2014 at 17:17

The "California Three-Way" could be wired similar to what you have shown. Fundamentally, it wires each wire of one three-way switch to the corresponding wire of the other; if the switches are in opposite positions, each switch will form a connection between the wiper and one other terminal, and thus the two non-wiper terminals will be connected.

The primary advantage of the California three-way as compared with running either two switched travelers to a remote switch and having it return the properly-switched line, or running hot to a remote switch and having it return two travelers is that the remote switch gets access to both hot and a properly-switched line without having to run an extra wire. The disadvantage of the California three-way is that parts of the circuit have no clear "upstream" and "downstream" relationship. In general, disconnecting all the wires upstream from a circuit will kill power to it. In the C3W configuration, that doesn't necessarily hold; one can disconnect the unswitched hot wire from part of a circuit and still have it receive power through switches. The safety risk from that is probably not as severe as the risks posed by the Carter system, but some building codes may still not allow it.

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