Red & Green twin core

[Me!]

As part of redecorating a room, I would like to fit some metal light units to replace the current plastic ones and so I need to earth them. The wires to the existing ceiling light are multiple single core neutrals, and also this one twin core red and green


I have never seen a cable like this before, nor can I find anything about it using Google. Testing it shows that the red is a switched live, but the green isn't unfortunately connected to earth. Does anybody know if it should be an earth please, or did the green core in red and green cable like this have a different purpose? There is no additional earth core between the red and green as in the way it is done in modern T&E.

From where this cable is in the house, I'd guess it is probably no older than 1970's, although it is hard to be sure that it wasn't already installed before then.

 

[88v8]

I've never seen that either.
But green was certainly the earth colour, so if you can find the other end you wouldn't be confusing anyone by earthing it.

And it's PVC. And single-core copper. Good stuff.

Ivor

 

[fernicarry]

Solid green was the colour for protective earth pre-1977, then it became striped green/yellow. I have a solid green earth bonding cable to the metal pipework in the loft. Would be very bad practice to re-use the protective earth colour for any other purpose but doesn't mean it didn't happen. As Ivor says best to find the origin of that cable and confirm whats really going on.

Take it this is at a ceiling rose? Odd for neutral to have been missing and added later in singles. Usually its the earth that's missing in old lighting circuits since didn't use to be required. If it were me I'd be very tempted to rewire the circuit for peace of mind. If you have RCD's on your board you'll need to make sure the neutral comes from the same section as the live, often neutrals get borrowed from other circuits if the are added later and that leads to problems. You're going to be decorating anyway...

 

[Flyfisher]

How curious. I'd guess it's not a terribly old cable because of the solid copper cores. Early PVC cables had multiple (usually three) tinned copper twisted cores. I'm not sure about when things changed to solid copper though.

Solid green was certainly the old colour for 'earth' but I'm not sure what application would only require true earth and live conductors. I agree with fernicarry about trying to find the other end of the cable and see how the circuit has been wired.

My guess is that the green conductor has been used as a neutral conductor, though goodness knows why.

 

[steveb]

What was the green connected to - or was it just floating loose?

 

[Me!]

Thank you for your thoughts.

The earlier photo showed the ceiling rose, where the red switched live was used and the green wasn't connected to anything. I do have RCDs and they don't suffer from any unexpected activations, so as the lighting in this room has been working fine for at least the 15 years that we have lived here I don't believe the neutrals have been borrowed between circuits.

Unfortunately I have just finished decorating this room though, so I'd really rather not start pulling down bits of ceiling now even though this one is only plasterboard, and there is another floor above so I don't really want to pull up a fitted carpet and floorboards either. So basically I don't know where the green goes and I don't think I can find out.

The lighting circuit in this room should be very simple. There is one switch at one door that turns on one ceiling light and one wall light at the same time.

So, as the wall light is on a hollow wall immediately above a ring-main socket, what I am currently doing is running just a single core earth up inside the wall from the power socket to the wall light and as the wall light is connected via a normal bit of red and black twin & earth to the ceiling light, that also gets me an earth at the ceiling rose. I'm then going to leave the green wire disconnected as it was when I found it. I know this means that I have connected a ring main earth to the lights for just this one room, but I can't see a problem with that, does anyone else think I shouldn't do it this way?

Many thanks.

 

[plasticpigeon]

My downstairs lighting circuit is odd. It has neutrals to the roses and lives to the switches. It then has switched lives to the roses. As there is an earth on the live and neutral circuits, the switched lives don't need to be earthed. Could that be the arrangement you have? At first I was going to rip it out, but it made sense once I worked out what was going on. I think it has a name but I can't remeber what this type of circuit is called.

 

[Me!]

As there is an earth on the live and neutral circuits

So have you got twin cables like mine to do that? I.E, do you have a cable with a red and a green in it, and perhaps another with a black and a green in it?

 

[MikeG]

Have you stripped back the outer insulation at all, to see if there is another wire hidden in there? Otherwise, have you pulled at the red or green sheaths to see if they are sleeves? I've certainly never come across a 2 core cable with just green and red, and can't imagine for a second why any such thing would ever have been manufactured.

 

[Me!]

Outer case now stripped back a bit further to confirm just red and green and nothing else -

 

[fernicarry]

So, as the wall light is on a hollow wall immediately above a ring-main socket, what I am currently doing is running just a single core earth up inside the wall from the power socket to the wall light and as the wall light is connected via a normal bit of red and black twin & earth to the ceiling light, that also gets me an earth at the ceiling rose. I'm then going to leave the green wire disconnected as it was when I found it. I know this means that I have connected a ring main earth to the lights for just this one room, but I can't see a problem with that, does anyone else think I shouldn't do it this way?

To be absolutely certain you'd need to make sure the earth on your lighting circuit has sufficiently low resistance to allow a large enough fault current to flow to operate the protective device. Slightly counter-intuitively you want as big a fault current as possible.

Measure the resistance between live and earth at the furthest point in the circuit -- or in your case the furthest point where both are present. Most meters aren't sensitive enough to give you this resistance since its expected to be very, very low, so you really need a sparky and his big expensive meter to do this. Divide into your nominal voltage (230) to give the fault current in amps. Typical MCB's guaranteed to operate at 5x rated current, so on a 6A lighting circuit you're looking for at least a 30A fault current or a resistance of less than 7 and a bit ohms. Occasionally lighting circuits have a C curve breaker so you need 10x rated current to operate it or under 3.8 ohms. Both those figures are very large for mains wiring so unlikely you won't meet them.

In reality your sockets are going to be on a larger breaker anyway so if the sockets are in spec your lighting circuit ought to be too. Be careful not to break ring continuity when you connect into the socket.

Have you had a look at your other ceiling roses? The other end of the green cable ought to be at another rose or back at the fuse box. But if you can't find it then that would be 'interesting'...

 

[Me!]

And if I temporarily connect a socket tester, it shows as no earth -

 

[Tom-H]

As above, the lives will be looped at the switches and the neutrals looped at the light positions - this used to be a common wiring method.

If you remove the light switch in that room, the other end of the cable should be there so check if all the earths are still connected there.

If all looks OK then it’s possible there is a fault elsewhere on the circuit and other lights could also be without an earth.

 

[plasticpigeon]

As there is an earth on the live and neutral circuits

So have you got twin cables like mine to do that? I.E, do you have a cable with a red and a green in it, and perhaps another with a black and a green in it?

I'm afraid not. Black and earth to the neutrals, red and earth to the switches and single core red with no earth as the switched live.

 

[Zebra]

How strange. Not seen red and green before. I wonder whether it's some specialist cable which a DIYer got hold of, or foreign even. It looks 60s/70s.

 

[a twig]

I have twin and earth, where the earth is fully insulated/sheathed in my house. The wiring dates back to the late 70s/early 80s - the earth on that is the same colour as yours.

Apparently this was available in the past as "damp proof" wiring. Rather than fix the damp problems, the previous owner just ran "damp proof" wiring :lol:

Interestingly the latest wiring regs in Ireland now mandate fully insulated earth - TE6193Y

 

[a twig]

On a more serious note, single and earth is a thing. Info on usage and example circuits here:

http://www.aaelectricalservices.co.uk/single-earth/

 

[CliffordPope]

, or foreign even. It looks 60s/70s.

I've just done a Google search for old European wiring colours, and French pre-1970 sometimes had Green for live and Red neutral.

 

[fernicarry]

On a more serious note, single and earth is a thing. Info on usage and example circuits here:

I can see the advantage of having fewer cables to mess around with at the ceiling rose, some fittings can be very fiddly, but the single cable is more expensive than the twin!

I'm more inclined now to go to the other extreme and drop a 3C+E from the rose to the switch position so that neutral is available there too. Required by some smart switches if you are into home automation. Also gives the option of taking a feed directly to a round pin socket from the switch location.

 

[Me!]

I've now looked at the wires to a few more ceiling roses in that part of the house, and they all have two single neutrals to them and one single switched live. No earth and no permanent live.
So I will probably never know why they used this mysterious red & green twin in just this one room, but I'm pretty sure that they only ever connected up the red. There is no sign of the green at the switch for that room, it only has one normal bit of red and black T&E going to it, so there must be some hidden junction box above the ceiling where the green ends up. The house was owned by an American during the 1970's, so maybe it was foreign-spec cable.

I do like Fernicarry's idea of using triple & earth to switches though, as that allows for much more flexibility in the future. Would that be legal to do it that way? Presumably though it would only work for circuits with one switch, as we'd run out of cores if trying to do a 2 or 3 switch circuit?