UK Old cable in dwelling light circuit

[RealNetworks]

We are currently renovating an old house after recently moving in. Whilst purchasing the property we received written assurances that the original 1920/30s wiring had been fully upgraded and subsequently tested.

After removing all of the downstairs ceilings, it is clear than new electric 2.5m2 and 1.5m2 cable/wiring has been installed, however there would appear to be an old and rather thick set brown fabric cable routing upstairs. Using a ‘non touch’ volt tester I was able to identify that the cable was live and part of the house light circuit. (The full house is on a single ring light circuit is, not ideal but it works). I noticed that this old cable routes into a round, brown junction box with the lid missing. The cable would seem to be an old 2 core cable with no earth present. Both cores are large ‘silver’ cables with several strands twisted together. I’m no electrician and therefore will refrain from touching it or proding around, however I would be grateful if someone would kindly advise if this cable should be changed, or indeed what it is. Everything works as it should, I’m just concerned that if we install new ceilings and it then needs to be replaced. The house is an old property and uses a TT system setup which I believe was upgraded with the installation of the EV charging unit. Any advice would be very much appreciated.

 

[littlespark]

Best course of action is get it replaced now, to ensure there is an earth present… done by a professional so you get the test certificates.

Whether there’s any comeback on the fact it was supposed to already have been rewired…. I don’t know.

When was it supposed to be rewired? If it was pre 1980’s, it possibly needs done again… just for increasing number of sockets more than anything.

Brown/blue colours are post 2007 and will be fine.

 

[davesparks]

That looks like a bit of VIR which is in surprisingly good condition if it is. As far as I know it shouldn't ever have been installed outside of conduit if it is VIR as its the equivalent of modern singles.

A non-contact voltage detector does not prove that it is live, it shows that it might be live. Likewise they do not prove that something is dead, they prove that it might be dead.
A disconnected cable sat next to a live cable will often cause a non-contact voltage detector to light up due to the capacitive coupling effect.

Does that cable actually connect to any of the new wiring?
If you've only found one end of it so far I'd suggest trying to carefully trace it to find the other end and see if it is connected.

Or else call an electrician to test it and see what's going on.

 

[RealNetworks]

Best course of action is get it replaced now, to ensure there is an earth present… done by a professional so you get the test certificates.

Whether there’s any comeback on the fact it was supposed to already have been rewired…. I don’t know.

When was it supposed to be rewired? If it was pre 1980’s, it possibly needs done again… just for increasing number of sockets more than anything.

Brown/blue colours are post 2007 and will be fine.

To be honest I tend to agree with you. I’ve traced the cable from the consumer unit right up to the loft. From there it feed into a junction box. Each wire from the junction box there after is subsequently 1.5m2 twin & Earth. What’s the point of the subsequent wire having an earth when the main feed doesn’t…it just makes no sense to me. I suspect the electrician who rewired the house found it too much trouble to re-routes a new main feed wire from the CU up into the loft for the lighting circuit. He then replaced the more accessible/visible wire. The out of sight mentally I guess - how sad! Hey ho. The rewiring was done in 2006. I completely agree however, the best thing to do is call an electrician to look at and ensure it is safe to use. as when I’ve traced the cable I found a junction box extending said wire. The condition mortified me. Can a professional electrician explain how this wast picked up on a test. I’ve attached a picture below.

 

[RealNetworks]

This is a picture of what I discovered.

 

[RealNetworks]

That looks like a bit of VIR which is in surprisingly good condition if it is. As far as I know it shouldn't ever have been installed outside of conduit if it is VIR as its the equivalent of modern singles.

A non-contact voltage detector does not prove that it is live, it shows that it might be live. Likewise they do not prove that something is dead, they prove that it might be dead.
A disconnected cable sat next to a live cable will often cause a non-contact voltage detector to light up due to the capacitive coupling effect.

Does that cable actually connect to any of the new wiring?
If you've only found one end of it so far I'd suggest trying to carefully trace it to find the other end and see if it is connected.

Or else call an electrician to test it and see what's going on.

I completely agree and understand that, but it is a useful tool for quickly providing a rudimentary reference point. The cable was live until I isolated the light circuit, and then live again. I’m just a little confused how live and neutral is identifiable without any markings. To be honest, the safest thing to do is have a electrician inspect the electrics in it entirety,

 

[westward10]

As above a volt stick is wholly unreliable. The fact it goes off when the circuit is isolated is no guarantee it is still live so it needs verifying with an appropriate voltage indicator.

 

[RealNetworks]

As above a volt stick is wholly unreliable. The fact it goes off when the circuit is isolated is no guarantee it is still live so it needs verifying with an appropriate voltage indicator.

I agree, I’m not implying it is 100% reliable. I’m simply explaining it was indicated. I’ve got my old Fluke 1653 multifunction tester I will use to determine any certainty.

 

[davesparks]

This is a picture of what I discovered.

That's not regular VIR then, that's something I've not seen before. It appears to be a coaxial 2 core cable with cotton tape and rubber insulation and a woven sheath.
@Lucien Nunes may be able to shed some light on what it is.

So to answer your question of how the cores are identified it is their physical position within the cable, the centre core will most like be live and the outer conductor neutral (may have been neutral/earth combined originally)

 

[RealNetworks]

That's not regular VIR then, that's something I've not seen before. It appears to be a coaxial 2 core cable with cotton tape and rubber insulation and a woven sheath.
@Lucien Nunes may be able to shed some light on what it is.

So to answer your question of how the cores are identified it is their physical position within the cable, the centre core will most like be live and the outer conductor neutral (may have been neutral/earth combined originally)

Reply, many thanks for the detailed response

 

[7029 dave]

I have not seen that type of VIR. Is this cable still in service (live), if yes then I advise the circuit/ circuits need rewiring.

 

[timhoward]

It reminds me a little bit of this photo, described on a USA wiki as "fabric- and rubber-insulated multi-strand electrical wire."

I'm not 100% sure it's the same though.
While it would be interesting to know what it is, whatever it is it pretty clearly shouldn't be in service.

At a minimum the CU end of this needs a good look at, some tests need doing at the junction box you found, and the lighting circuit downstream of it needs testing for the presence of a CPC and absence of any other supply.

Quite aside from any issues from the elderly cable, if there are any metal lights or switches then there is a pressing safety issue if the lighting circuit isn't earthed. It might be that the subsequent T+E has an earth connection from another circuit. (This is permitted by the regs if sized correctly)

But really it needs someone to take a good look at it, soon.
It might be worth sharing (vaguely) what area you are from as there may be a forum member nearby that can help you.

 

[RealNetworks]

Thanks everyone. I can’t disagree with anyones comments and or advice, it’s been very helpful.

It’s certainly an interesting one. Every other wire on this circuit is 1.5m2. I’ve also notice this wire connects to a 1.5m2 wire before entering the CU. Effectively, the electrician has installed new wire either side what would’ve been a complicated run of wiring from downstairs up through to the loft.

 

[telectrix]

@OP. ifyou post your rough location, 1 of us may be close enough to have a quick look and advise.

 

[RealNetworks]

@OP. ifyou post your rough location, 1 of us may be close enough to have a quick look and advise.

Excellent idea. Northumberland.
To be honest, I think the whole property requires a complete rewiring. Whilst my background is a Network Engineer and I’m quite happy doing small electrical jobs and understand the logic and principles involved. However under no circumstances, is it ever good idea for a DIY or amateur to consider replacing cables or messing around in the CU. Others may disagree, but quite frankly is the risk worth it? I don’t think so. It’s important to understand what installation you have and how it works, but leave the doing it to professionals.

 

[westward10]

It is two core it is just that the red insulation has all but gone but you can just still see it. It is more like PBJ that that was normally single core meter tails.

 

[RealNetworks]

It is two core it is just that the red insulation has all but gone but you can just still see it. It is more like PBJ that that was normally single core meter tails.

How would they’ve earthed the circuit as there is no cpc present. I think moving forward the sensible thing to do is have a EICR done. In the meantime for peace of mind, whilst I don’t like meddling with mains electric, I’m competent enough to use my Fluke multifunction tester to do some rudimentary testing. Therefore I will do a r1, r2 + rm and Zs and Ze as I’m not convinced about the external cpc. I will report back.

 

[littlespark]

They may have borrowed a cpc from another circuit…. Upstairs sockets or whatever…

It needs replaced anyway.



I’m close to Northumberland…. But only the top bit.

 

[RealNetworks]

Just a quick note. As I really don’t recognise this cable, I’m wondering do any of these old fabric cables contain asbestos in their inner insulation?

 

[westward10]

Not likely to contain asbestos and it may not even be live a voltage indicator will quickly prove this.

 

[RealNetworks]

Not likely to contain asbestos and it may not even be live a voltage indicator will quickly prove this.

No it’s live, so far initial testing would indicate it is part of the ring circuit for the house lights - Yes I know, all the lights on a single circuit. If this is the main connection to upstairs, it may be a good idea to split the ring and have an upstairs and downstairs both on radial circuits. Further testing will be needed before deciding this however.

 

[7029 dave]

No it’s live, so far initial testing would indicate it is part of the ring circuit for the house lights - Yes I know, all the lights on a single circuit. If this is the main connection to upstairs, it may be a good idea to split the ring and have an upstairs and downstairs both on radial circuits. Further testing will be needed before deciding this however.

Dont mean to be pedantic but lighting circuits are radial circuits. I would be very worried if it was a ring circuit.

 

[timhoward]

How would they’ve earthed the circuit as there is no cpc present. I think moving forward the sensible thing to do is have a EICR done. In the meantime for peace of mind, whilst I don’t like meddling with mains electric, I’m competent enough to use my Fluke multifunction tester to do some rudimentary testing. Therefore I will do a r1, r2 + rm and Zs and Ze as I’m not convinced about the external cpc. I will report back.

To be honest, while you could test and prove it is or isn't earthed, its a little bit academic as if that's the supply to the lighting it needs replacing.
It would be helpful/reassuring to know if the circuit is currently RCD protected.

Excellent idea. Northumberland.

I know we said rough, but Haltwhistle to Berwick is a fair trek! (I used to live in Carlisle and love the area you live in).
Are we allowed at least the start of the postcode?!

 

[littlespark]

To be honest, while you could test and prove it is or isn't earthed, its a little bit academic as if that's the supply to the lighting it needs replacing.
It would be helpful/reassuring to know if the circuit is currently RCD protected.

I know we said rough, but Haltwhistle to Berwick is a fair trek! (I used to live in Carlisle and love the area you live in).
Are we allowed at least the start of the postcode?!

Berwick postcode will throw you off… It’s TD, when everywhere else is NE

 

[timhoward]

Berwick postcode will throw you off… It’s TD, when everywhere else is NE

Yeah! I recall it's been in England and Scotland a fair few times.... I've no idea if the story about it remaining at war with Germany or Russia by accident is true but it's a good story nonetheless!

 

[davesparks]

Dont mean to be pedantic but lighting circuits are radial circuits. I would be very worried if it was a ring circuit.

I wouldnt be worried as there's nothing wrong with wiring lighting as a ring, it's just very unusual.

What also may happen is someone may assume there is a ring if there are two cables in an RCBO.

 

[davesparks]

No it’s live, so far initial testing would indicate it is part of the ring circuit for the house lights - Yes I know, all the lights on a single circuit. If this is the main connection to upstairs, it may be a good idea to split the ring and have an upstairs and downstairs both on radial circuits. Further testing will be needed before deciding this however.

You say this is the main run to upstairs and also have said this connects to a cable coming out of the CU, are there two lighting cables coming out of the CU by any chance? Ie two cables connected to the same MCB or RCBO?

 

[RealNetworks]

Dont mean to be pedantic but lighting circuits are radial circuits. I would be very worried if it was a ring circuit.

Indeed you would think. However I am assuming it has been wired as a circuit as there are two wires in to MCB. Surly you wouldn’t except 2 radial circuits to be wired in to the same MCB? Nevertheless I am pressuring but will have a better idea tomorrow. But as said above, we’re just going to have it replaced before having new ceilings installed. Better to be safe than sorry. I’m just curious to know what type of wire it is as I’ve never seen its like before. It’s using a 6am MCB with an RCD so I hope the electrician will only need to replace this wire with a new run of 1.5mm2 cable but in all truth I won’t know until I have the EICR completed.

 

[davesparks]

Indeed you would think. However I am assuming it has been wired as a circuit as there are two wires in to MCB. Surly you wouldn’t except 2 radial circuits to be wired in to the same MCB?

This suggests there may be further issues.

I suspect there may be what's called a borrowed neutral between what was originally two lighting circuits and instead of fixing it they have put both cables into the one MCB to make it safe.

 

[RealNetworks]

You say this is the main run to upstairs and also have said this connects to a cable coming out of the CU, are there two lighting cables coming out of the CU by any chance? Ie two cables connected to the same MCB or RCBO?

You’re spot on Dave but it is an MCB not an RCBO. One of the cables from the CU go to round brown junction box and connects to this wire. I haven’t fully traced the other cable yet.

 

[telectrix]

Indeed you would think. However I am assuming it has been wired as a circuit as there are two wires in to MCB. Surly you wouldn’t except 2 radial circuits to be wired in to the same MCB? Nevertheless I am pressuring but will have a better idea tomorrow. But as said above, we’re just going to have it replaced before having new ceilings installed. Better to be safe than sorry. I’m just curious to know what type of wire it is as I’ve never seen its like before. It’s using a 6am MCB with an RCD so I hope the electrician will only need to replace this wire with a new run of 1.5mm2 cable but in all truth I won’t know until I have the EICR completed.

not unusual to have 2 lighting circuits in 1 MCB, but then, by definition, they both become 1 circuit.

 

[RealNetworks]

This suggests there may be further issues.

I suspect there may be what's called a borrowed neutral between what was originally two lighting circuits and instead of fixing it they have put both cables into the one MCB to make it safe.

I very much think you are right. I would rather 2 separate circuits, 1 for upstairs and 1 downstairs to allow lighting in the event one area goes down. This wouldn't be an option if both wires are using the same MCB. The only correct way to do this is to replace the entire circuit with new cable. As we’re eliminating the circuit we wouldn’t need to use 3 core with cpc and therefore only need normal 2 core with cpc. Having looked at some of the 2 way switches, there are some single 1mm cables with 2core and cpc. I’m suspecting tge borrowed neutral is going to be in one of these switch/connections.

 

[Lucien Nunes]

That does look like concentric cable, rather than twin with all the red insulation missing. Inner conductor, plain rubber insulation, outer conductor, cambric tape and compounded braid sheath. Very rare stuff, I've been collecting cables for 30 years and never seen any of that before.

Interestingly it appears to be 7/.029, going by the size relative to the JB terminals and the fact that .029" was the smallest strand generally used in non-flexibles. This is a larger cable than needed for any normal lighting circuit and, allied with the fact that this type of cable was rarely used in domestic work, I wonder whether it was installed separately to the original installation perhaps as a repair, by someone who had some surplus on hand.

Concentric cable achieves its compactness and enhanced rating in part by having reduced or no insulation over the outer. This imposes the requirement that the neutral conductor is reliably earthed which was not always done until after the war and the amendments to the 11th edition, and sometimes required permission from the supply company. Use of concentric wiring would tend to be a deliberate choice, very often following a proprietary system, not one made on a whim by the installer. It might have been done to the specifications of an engineer who was personally keen on the idea, more likely in the 20's than 30's.

I would be very grateful for an opportunity to save whatever of it you can get out intact, for the museum. Old rubber cables don't always withstand removal without crumbling, but the longer the pieces you can get, the better. I will happily pay for you to pack it in a box and send it down. Even if you can only get short stubs as samples, they are still interesting.

In the meantime when I am next in the museum store I will try to find a reference to it in a catalogue.

 

[pirate]

Thank you Lucien...really interested in such things, and love your knowledge.

 

[Aaron b]

That looks like a bit of VIR which is in surprisingly good condition if it is. As far as I know it shouldn't ever have been installed outside of conduit if it is VIR as its the equivalent of modern singles.

I didn't realize it was supposed to be in conduit in floors. I've seen it through conduit in the walls but usually fed through small holes in the joists around here.

 

[RealNetworks]

That does look like concentric cable, rather than twin with all the red insulation missing. Inner conductor, plain rubber insulation, outer conductor, cambric tape and compounded braid sheath. Very rare stuff, I've been collecting cables for 30 years and never seen any of that before.

Interestingly it appears to be 7/.029, going by the size relative to the JB terminals and the fact that .029" was the smallest strand generally used in non-flexibles. This is a larger cable than needed for any normal lighting circuit and, allied with the fact that this type of cable was rarely used in domestic work, I wonder whether it was installed separately to the original installation perhaps as a repair, by someone who had some surplus on hand.

Concentric cable achieves its compactness and enhanced rating in part by having reduced or no insulation over the outer. This imposes the requirement that the neutral conductor is reliably earthed which was not always done until after the war and the amendments to the 11th edition, and sometimes required permission from the supply company. Use of concentric wiring would tend to be a deliberate choice, very often following a proprietary system, not one made on a whim by the installer. It might have been done to the specifications of an engineer who was personally keen on the idea, more likely in the 20's than 30's.

I would be very grateful for an opportunity to save whatever of it you can get out intact, for the museum. Old rubber cables don't always withstand removal without crumbling, but the longer the pieces you can get, the better. I will happily pay for you to pack it in a box and send it down. Even if you can only get short stubs as samples, they are still interesting.

In the meantime when I am next in the museum store I will try to find a reference to it in a catalogue.

Fascinating and extremely interesting. Thank you for taking the time provided all of tris information. And of course, it would be my pleasure. From the research I’ve done regarding the property, it originally had gas lights fed through led pipes. However in 1929 it was wired with electricity. We are located in a rural location. Obviously in the 2000s it was then once again rewired. The wire is in generally very good condition and I’m sure I will be able to retrieve a good 4-5 meters if that was of any use to you. I would be happy to provide you with some information documenting the property and the chaps who built it, a rather sad story. I will pm you once it has been removed.

 

[davesparks]

I very much think you are right. I would rather 2 separate circuits, 1 for upstairs and 1 downstairs to allow lighting in the event one area goes down. This wouldn't be an option if both wires are using the same MCB. The only correct way to do this is to replace the entire circuit with new cable. As we’re eliminating the circuit we wouldn’t need to use 3 core with cpc and therefore only need normal 2 core with cpc. Having looked at some of the 2 way switches, there are some single 1mm cables with 2core and cpc. I’m suspecting tge borrowed neutral is going to be in one of these switch/connections.

The most common borrowed neutral situation is a single core live taken from the downstairs lighting circuit to the 2 way switch at the bottom of the stairs. Then a twin is taken from downstairs switch to upstairs switch and another single, the switched live, taken from their to the light above the stairs. This light would then have its neutral connected to the upstairs lighting circuit. Thus the two circuits become linked, and quite dangerous for anyone working on it.

 

[Lucien Nunes]

I will be able to retrieve a good 4-5 meters if that was of any use to you. I would be happy to provide you with some information documenting the property and the chaps who built it, a rather sad story. I will pm you once it has been removed

Thanks!

The fact that it is rural adds another possible dimension, which from your research you might be able to dismiss or not, and that is whether the original wiring was powered from a generating plant rather than a connection to the public supply. If the property had its own lighting plant, the voltage might have been well below modern mains voltage. 50V and 110V were popular choices, and especially in the case of 50V, larger conductors might have been used hence the 7/.029 for lighting.

I didn't realize it was supposed to be in conduit in floors. I've seen it through conduit in the walls but usually fed through small holes in the joists around here.

We need to be careful and clear with the terminology here. 'VIR' (Vulcanised India Rubber) normally referred to single-core insulated cables without sheath, intended for installation in conduit just like modern singles e.g. 6491X. The external surface of VIR is the braid, not the rubber itself.

'TRS' (Tough Rubber Sheath) normally referred to rubber-insulated and sheathed cables made like modern flat twin and earth, with two or three insulated cores, optionally an uninsulated earth, and an overall extruded rubber sheath. This is not intended to be run in conduit. The term TRS is still used with the same meaning today, mostly in reference to flexibles e.g. H07RN-F

The OP's cable, if it is what it appears to be, is something of an oddity. The outer conductor doesn't need insulating so there is no rubber around it, only the braid. This gives it the appearance of single-core VIR when it actually serves the purpose of 2-core TRS. There were flat twin rubber-insulated cables with braid overall but these are also rare. I do however have samples of a couple of varieties.

 

[Aaron b]

Was the lead covered flat cable used at the same time as vir singles? I've never seen it terminated.

 

[Mike Johnson]

The volt stick pro with the shielded tip is very sensitive and will not indicate on the neutral side of T&E its an advance on the normal volt sticks: Volt Stick instant non-contact voltage testers - https://voltstick.com/products/selective

 

[Lucien Nunes]

Was the lead covered flat cable used at the same time as vir singles? I've never seen it terminated.

Generally yes, but lead fell out of use earlier. Where cost was the main consideration, TRS was cheaper than lead and increasingly found acceptance for domestic work. Where durability was the main consideration, VIR in conduit had always been and remained the system of choice. TRS was superseded by PE/PVC T+E, VIR singles by PVC singles. Lead sheaths kind-of fell through the gap in the middle for building installations, although continued to offer advantages for underground cables.

Lead twin was normally jointed using pressed metal JBs with screw-down clamping bars at the cable entries to connect the sheath to the box. At fittings such as roses and switch pattresses, continuity could be maintained and/or a connection could be picked up off the sheath using screw-on clips, or by pairs of flat bars that could be clamped around multiple cables. These were called 'bonding bars' because at that time 'bonding' meant maintaining earth continuity generally, rather than specifically connecting extraneous conductors to the equipotential. For ironclad fittings and switchgear there were saddle-type clamps that screwed into the conduit entries.

Because lead flows easily, these various clamping methods did not remain very tight. Although continuity was normally maintained, it was recognised as a weak spot and for high-class lead work even by the early '30s there was the option of lead twin with a bare tinned copper CPC inside, in contact with the sheath. This was terminated in the JB in the usual way offering a reliable CPC connection to both the sheath and the next point.

 

[telectrix]

The volt stick pro with the shielded tip is very sensitive and will not indicate on the neutral side of T&E its an advance on the normal volt sticks: Volt Stick instant non-contact voltage testers - https://voltstick.com/products/selective

got one. ideal for when you have multiple cables in back of a switch. bloody expensive though, was >£30.

 

[RealNetworks]

The most common borrowed neutral situation is a single core live taken from the downstairs lighting circuit to the 2 way switch at the bottom of the stairs. Then a twin is taken from downstairs switch to upstairs switch and another single, the switched live, taken from their to the light above the stairs. This light would then have its neutral connected to the upstairs lighting circuit. Thus the two circuits become linked, and quite dangerous for anyone working on it.

This is precisely what has been done, although it is initiates im the downstairs hallway which is also controlled by a 2 way switch. It is such a mess. I’ve also noticed that at every junction box the installer has simply twisted the individual CPC together at the back of each box. Whilst it’s not necessary dangerous as such, it is bad/lazy practice. Indeed at 2 junction box on the final ring, the CPC has separated. I’ve replaced each junction box with new Wago box and connected the CPC securely. It really is quite a mess.

 

[Lucien Nunes]

@RealNetworks, Hope your renovation is going OK. Just curious if you managed to liberate this cable yet?

 

[RealNetworks]

@RealNetworks, Hope your renovation is going OK. Just curious if you managed to liberate this cable yet?

Unfortunately very slow!!! It will hopefully be removed over the next 4 weeks and I will make sure that I inform you. All the best

 

[RealNetworks]

@RealNetworks, Hope your renovation is going OK. Just curious if you managed to liberate this cable yet?

Sorry for delay! Cable fully liberated now I have retained a good few meters for you. Message me so we can arrange postage

 

[Mike Johnson]

@RealNetworks You must be the only person on here who does not know that Lucien died a month or so back, but it's good to see his legacy lives on.

 

[RealNetworks]

@RealNetworks You must be the only person on here who does not know that Lucien died a month or so back, but it's good to see his legacy lives on.

Really, what awful news. I feel terrible. He was incredibly helpful. Thank you for letting me know.