ring main woes

Hello,

Is there a rule that you should re-wire a house every x years, and if so, what is x?

The wiring in our house is, I presume, the original from the 1970s. Rather than run T&E to the lamps, the builders/electrician has used conduit cable. The electrician that visited told us he hadn't seen anything like it, though he was younger than the house!

The problem is that in the 1970s we didn't have pcs, dvds, etc and all the sockets were put onto one 32A ring main. To be fair that's not a problem under normal use but other houses we have lived in have had two ring mains; usually one for upstairs and one for downstairs or one for front and one for back of the house.

Recently I was working on the CH during a cold spell, so we had a couple of fan heaters on. The problem was that a couple of 3kW fan heaters and a kettle, left little room for anything else, so the mcb tripped once or twice.

The CH is up and running now, so hopefully we will not need the fan heaters for a while, but it would be nice to divide the ring main into two. I think it would be useful to divide the ring logically, e.g. all upstairs on one; all downstairs on another (incidentally they did this with the lights, so why no the sockets?). I don't suppose this is possible? I suppose the ring main lies between the up and downstairs floors and drops down into the ground floor rooms and up to the upstairs alternately? Would I have to settle for a front of house/back of house divide?

Is it just a matter of disconnecting one end of the ring and then disconnecting at different sockets to see which are powered or is there any easier way to trace the ring main?

Once it is split in half, is it just a matter of adding a new T&E tail to each half, back to the CU to convert the two radials into two rings?

Thanks.

Reply to
Fred
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Around 60 for a total rewire, and 30 for a damn good check.

Anything is possible, bu the time taken to work out how to do it may exceed the time to lay a complete pair of rings.

Not necessarily, but it does get tricky..

Essentially yes but really, by the time you have done all that its easier to hoick up all the floorboards ad do it all over again.

I would strongly recommend a bit of bullet biting, a new consumer unit, and a totally modern installation: If some of the original cable can be used regard that as a bonus.

Just don't expect it.

Reply to
The Natural Philosopher

On Mon, 18 Feb 2008 14:10:56 GMT someone who may be Fred wrote this:-

Not much of an electrician if he can't cope with conduit.

It would be nice.

They were economising.

Most things are possible. However, in extending conduit one either needs to use conduit, or measure and calculate carefully whether some other sort of cabling system like twin & earth can be added to the system safely. There are a number of pitfalls in this to do with fault currents and ensuring a proper earth connection everywhere.

Unless you have the skills to slowly DIY all this the cheapest option will be to get someone else to install two new ring mains.

It would also be worth testing the existing system to check on disconnection times. Sometimes conduit can rust to the extent that it goes high impedance.

Reply to
David Hansen

used in conduit). You do not imply that conduit is used.

I did a lighting circuit like that in the '60's - but the wire was double insulated and at the time suitable for burying in plaster. Is yours double insulated singles?

A cable of 3 strands of 0.029" was used. The red and blacks had an outer grey sheath.

Reply to
John

I'm sorry if I have used the wrong term. I think the other poster thought conduit had been used as an earth? That's not the case. I didn't know that was allowed. The ring main for the sockets is (as far as I have seen) wired in T&E.

I think I have confused the issue by saying that the lighting circuit, but only the lighting circuit, is wired in what I thought was called "conduit cable"; you are right that what I meant by this is that a double sleeved black neutral wire runs to each light and a double sleeved red (or rather two of them) run to and from the switches.

As it happens the inner and outer sheaths are the same colour.

Reply to
Fred

Thanks. The CU looks relatively modern (mcbs rather than fuses); it's a shame they didn't modernise everything else at the same time!

The problem with a re-wire is that it requires lifting all the carpets and a lot of floorboards so it becomes a big job. That would not be so bad because carpets and boards can be re-laid but my worry is getting the wires down the walls. No doubt they are plastered in and will require half my walls to be demolished too!

Reply to
Fred

I have been thinking about this some more. The house was built in the

70's, so we are at the "damn good check" distance. What is involved in a damn good check? Like the other poster said, if you have to lift everything to go looking, I suppose you may as well replace everything at the same time?
Reply to
Fred

So it is wired in Twin Sheathed Single Cables. What do the experts make of that? I guess it is ok?

Reply to
John

I'd say that was a trivial issue. If there's no earth wire, thats less than ideal, and its best not to use any metal light or switch fittings. Once its buried in plaster its no more or less drillable than T&E, and the risk of cable drilling is tiny anwyay.

NT

Reply to
meow2222

No. Once you get as far back as the 60s then the need to rewire becomes high. And if the 60s wire is rubber insulated, fairly certain.

singles

The problem you describe sounds trivial, and the solution you propose sounds far more inconvenient. So it doesnt make a lot of sense really.

If you want to split the ring, yes as you say 2x T&E runs back to the CU. You dont know how the existing wiring is routed so you wont get a halfway split, unless by chance, and it doesnt matter anyway. Just pick the furthest point from the CU to split it to maximise the amount of socket distribution.

But really I cant see any point in it.

70s installs are normally ungenerous but adequate capacity-wise, imperfect but pretty good safety wise, totally inadequate in terms of number of sockets, and quite often have been subject to various inexpert bits of rewiring that need sorting out safely.

So with such an installation if you dont know its history an inspection should pick up any issues that need sorting - but bear in mind it will also pick up issues that don't. There is no practical or legal reason such installs would need to meet the regs for a new install, but any spark touting for business will pretend it must.

Re socket provision, lots more sockets can be added to an existing ring without causing a problem. More sockets doesnt change system capacity.

NT

Reply to
meow2222

There are no hard and fast rules. The design life of PVC cable running continuously at its full rated load is 25 years, but of course the actual loading pattern of house wiring usually comes nowhere near that, making cable life effectively indefinite (apart from specific issues such as cables affected by the 'green goo problem').

It's recommended that a formal 'periodic inspection report' (PIR) is commissioned every 10 years, although this is seldom observed in practice in owner-occupied premises. The purpose of a PIR is to assess whether an electrical installation remains safe for continued service. A PIR consists of a thorough visual inspection of the installation together with relevant testing - insulation resistance, earth fault loop impedance, RCD operation, etc. The report follows a standardised format and includes schedules of inspections and of test results, the later identifying all the final circuits. Issues identified are 'coded' for severity: code 1 = immediate danger, 2 = requires improvement, 3 = requires further investigation and 4 = not compliant with current regs but not necessarily dangerous. Assessment is always to the current version of the regs, so older installations will always throw up a number of code 4s, and possibly the worse code 1s and 2s. Effective PIR-ing needs a knowledgeable electrician, preferably one holding the C&G 2391 qualification.

You have to ask yourself whether it's worth the bother, if/when use of electric heating will be pretty rare. If it won't be rare you could consider adding one or two dedicated radial heating circuits instead.

It happens naturally for lighting circuits which tend to have one 'tail' for each floor.

If your house has a suspended timber ground floor you'll probably find that one end of the ring goes under the ground floor floorboards, loops round all the ground floor sockets and then rises somewhere for a similar loop upstairs. If that's the case then cut the rising section and join on two new ends.

You'll probably need to use a mixture of visual inspection, selective disconnection and continuity testing to work it out.

Essentially yes, although, since you are modifying circuit(s) it will need to comply with current regs, including 30 mA RCD protection (sockets likely to be used for portable equipment outdoors) and the adequacy of the underlying earthing an bonding.

Reply to
Andy Wade

If it's rubber, should have been done ~30 years ago. If it's PVC, then even the earliest PVC installations should still have sound cable unless it's got hot, and should remain good for decades yet. IEE estimates 1000 year live of the PVC in ideal conditions, dropping to

21 years for a cable operating continuously at max rated temperature of 70C. Some wiring schemes such as conduit can suffer high earth impedance after a long time.

Wiring accessories (switches, sockets, fuse box, etc) will not generally last as long as the wiring and should be checked periodically -- life will depend on usage and original quality. Fortunately, they are much easier to replace than the wiring. Also check for terminal screw tightness, as poor contacts there can lead to heating and damage to accessories and cable (and worse).

Standards and expectations change over the years. A 50 year old PVC installation could still be in perfect order, but would be lacking the number of sockets expected today, and below current earthing standards. That doesn't necessarily mean a rewire is required, but poorly done piecemeal expansion of an original installation is a common cuase of an installation having become an unrepairable mess.

My parents installation was one for earliest PVC ones in the 1950s. The original accessories are all MK, except the fusebox which was Wylex. I found the fusebox was in need of replacing 10 years ago during an inspection -- the contacts on the ring circuit fuse holder were getting too hot and caused insulation to go brittle. I replaced the fusebox as part of rewiring/refitting the kitchen and bringing service bonding up to spec. I can only think of one of the MK accessories which has failed -- a light switch. About half of them have been replaced during room redecorations over the 50 years, but none had anything wrong with them. A few of the terminal screws have been retightened.

Reply to
Andrew Gabriel

That's interesting - have you got a reference for that? Was it just a 'think of a number' when PVC cable was introduced? Clearly there are different qualities of PVC (not only for cable insulation/sheathing).

Most of my wiring is (AFAIK) original, the house having been built around 1973. The original stuff is stranded, so it's likely to be

7/0·029 for the sockets, although I've never measured it. Generally it seems to be in good condition. Not that it runs anywhere near its full rated load!
Reply to
Frank Erskine

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more detail.

Hmm, not so sure about 7/0.029 in 1973. Cable went metric around

1969-70, IIRC. 2.5 mm^2 was, and still is, available in stranded form (7/0.67 mm IIRC). Generally 7/0.029 to BS 2004 will have tinned conductors and metric to BS 6004 will be plain copper.
Reply to
Andy Wade

Could you expand a little on the 'green goo' and why it's a problem?

TIA

Reply to
Terry Fields

No, it's a concrete ground floor I'm afraid, so I think the cables drop from above.

Reply to
Fred

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to Dr. Jeremy Hodge of BASEC.

Green gunge / goo from older PVC cables

--------------------------------------- Green gunge (sometimes called green goo) is sometimes seen exuding from the ends of some older PVC insulated and sheathed cable. This is seen in some cables made in the 1960s and 1970s, but is not generally seen in modern PVC cables.

Its origin is the plasticiser used to provide flexibility in the PVC polymer compound. This is generally di-octyl phthalate, which over time or with excessive heat has reacted with the copper conductors to produce copper phthalate (hence the green colour) suspended in the liquid plasticiser. The material is of health concern, so should be handled with care ? gloves should be used and waste disposed of properly.

Industry guidance is generally as follows, if green gunge is seen. Although there does not appear to be a problem with the electrical performance or safety of the cable itself, any exuded gunge should be removed as it can cause corrosion or affect the action of switches and terminations, potentially resulting in tracking / overheating. It can also cause cosmetic problems such as staining. The affected circuits should be rewired as soon as possible.

The original manufacturer of the cable should be contacted if there are any additional questions.

HTH

Reply to
Andy Wade

On Wed, 20 Feb 2008 08:55:32 GMT someone who may be Fred wrote this:-

Separating the floors out is going to be complicated. Perhaps something for a leisurely DIY task. It will be far more rapid to install new cables from scratch.

However, there is no reason to separate floors in a domestic building. It is only done that way for ease of wiring. It may be more logical to separate circuits by the area they are in. For example rooms on all floors in a particular corner of the house. That may make the re-arrangement a lot easier, but it depends on how it is currently wired. We don't know how the house is wired and have no way of finding out. Only you can do that.

Reply to
David Hansen

Many thanks.

Reply to
Terry Fields

When I used to do re-wires some years ago I preferred to use Double insulated singles (with earth) for the lighting circuits. It made life so simple, dropping a nuetral round all the lamp holders and also allowed you to keep the colour coding right i.e. the return live from the switch. (red instead of black when you use TW&E) However, I don't see double insulted singles on sale today well not 1 or 1.5mm anyway.

Is that because it's not an approved way anymore ? Are there circumstances where it should it be replaced. i.e If you where, as the OP would like to do, spliting the light circuits into two domains would the Part P inspector expect any "double insulated singles" to be replaced with TW&E.

Reply to
ac1951

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