Life of electricl wring?

[alan.holmes]

How long would expect today's electrical wiring to last, 10 years, 29 years,

30 years or much longer?

What determines the age at which wiring needs to be changed?

Alan

[Dave Osborne]

The life of modern electric wiring is indefinite. PVC insulated copper cable will last indefinitely. PVC-Insulated cable came in at the end of the 1950's and fifty years on, the vast majority of it is in entirely acceptable condition. There will be some PVC cable which has deteriorated as a result of exposure to the ultraviolet component of sunlight and there will be some PVC cable which has deteriorated as a result of exposure to expanded polystyrene. But, on the whole apart from becoming stiffer with age, 50 year-old PVC should still be like new.

There are still modern-pattern accessories in use from when they were first installed 50 years ago and again, as long as they are not physically broken, or worn-out due to excessive arcing or overheating due to loose terminals (which effects in themselves have little to do with average life expectancy) they are perfectly serviceable.

Accessories these days have become something of a fashion item, so tend to be replaced more often than fixed wiring.

Consumer units and circuit protection have come a long way in their sophistication in the last fifty years, but old-fashioned rewirable fuse carriers still abound and still provide basic protection against fire, which remains their primary purpose.

Any house with vulcanised rubber cable should really be a prime candidate for rewiring as the ends of the cable where they get hot are usually significantly deteriorated. And designs using such cable often do not incorporate adequate earthing arrangements

As the use of electricity has abounded since the second world war, modern installation practice has (in the form of the IEE Wiring Regulations) been regularly updated to reflect the increased use of electricity around the home and to leverage improvements in safety devices and techniques which help to prevent electric shocks.

So, in summary, modern electric wiring will last at least another fifty years. No doubt accessories will continue to be changed regularly as fashions dictate and no doubt the sophistication wiring system design will grow.

HTH DaveyOz

[Andrew Gabriel]

The life estimate is around 1000 years at 30C, reducing to 22 years IIRC at max temperature (70C for regular PVC). At the upper limit, you aren't ever likely to replace PVC cabling because it's worn out - the motivation to do so is going to be something else.

I've never found any which has, even with decades of exposure.

Any polystyrene will do it. I occasionally find some polystyrene T&E cable clips, which look like they've slightly melted into the cable.

50 year old accessories IME are suffering failures. Need to be particularly careful of those which generate heat such as high current circuit accessories including the CU. In addition to wearing themselves, the heat very significantly reduces the cable life over time. Fortunately the wiring accessories are relatively easy to replace, verses the cable itself.

and should be.

Another problem with older installations is likely to be not enough socket outlets though.

[js.b1]

Cable temperature based projections:

- IEE 16th commentary cites that PVC cables with a conductor operating temperature of 70oC for 24hrs/day have a lifespan of 23yrs, for 8hrs/ day have a lifespan of 69yrs and for each 8oC increase in core conductor temperature above 70oC the cable lifespan is halved.

- In a domestic environment a cable is not running at 100% for even

8hrs/day thus a domestic installation lifespan is potentially far beyond 69yrs.

- Life termination is defined as the appearance of cracks on samples of cables wound on their own diameter.This is something of a simplification, it is nearly always the cable end terminations (localised heating) which determine the cable's end of life status.

- 1950s PVC is in fact PVC sheath with polyethylene insulation. Localised heating caused by loose terminals makes the translucent red insulation appear to be brown with circumferential cracks exposing copper. If sufficient spare cable exists it can be stripped back & re- terminated (or ideally that run replaced).

- 1984 PVC is PVC sheath with PVC insulation. A nearby kettle combined with damp solid brick wall had resulted in a rotted green & brown 2G backbox. On cutting the cable it was found to essentially shatter lengthwise along its sheath like rigidised PVC, I summise terminal resistance had increased causing localised heating which conducted back along the immediate cable.

Lifespan can be reduced by obsolescence: Early PVC FTE 2.5mm had a 1.0mm CPC which restricted final circut length due to EFLI limitations, later PVC cable used a 1.5mm CPC. Interestingly PVC FTE 4.0mm suffers the same limitation but has not seen a CPC increase, perhaps due to the cost implications making it even more unattractive compared to rings wired in FTE 2.5mm.

[John Rumm]

Worth also mentioning that when 1.0mm^2 CPCs are combined with 30A BS3036 re-wireable fuses, you typically end up with spurs that are under protected against fault currents.

[alan.holmes]

Can I ask where did you find this information?

Alan

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