Estimated Age Of Wiring System

Estimated Age Of Wiring System

When completing electrical inspections as part of an Electrical Installation Condition Report, one of the boxes asks for the estimated age of wiring system.

Whilst this may seem like an easy, quick check, it can often be more difficult to accurately estimate the age of the wiring than you would imagine.

Dating old wiring can be made difficult due to the fact that different parts of the installation are often updated independently of other parts.

For example, it is common that the consumer unit or fuse board is often newer than the actual cables themselves. This is due to the fact that these items are usually upgraded before the wiring would be considered to be due for upgrade.

Dating Old Electrics

The first thing to really notice when you are working out the estimated age of wiring system is that neither the service head, nor the fuse board/consumer unit are a reliable indicator of age.

The best clue to the age of the wiring is the cable itself. This is the main bulk of the wiring system and gives the best indicator of age.

When dating old electrics always inspect the cables installed at the property.

Age of Old Wiring & Cables

The cable itself gives a number of clues about it’s age. This can be in the form of colours, or also in the type and construction of cable.

The most obvious modern cable is PVC Twin & Earth. This contains 2 equal sized insulated conductors (Live & Neutral) and a bare central CPC which is slightly smaller (in line with adiabatic equation).

First up is the colour of the insulated conductors. Blue & brown insulated conductors for L&N were first introduced in 2004. There was a small crossover period where stocks of red & black T&E cable were allowed to be used up.

Prior to this, Live was red & Neutral was black in UK installation wiring. If you come across black and red cables, you can be sure that they are at least 15 years old by now.

Going back further still, before metric cable, T&E wiring was imperial sizes. This is easiest to identify at sockets where instead of 2.5mm solid copper conductors, there are 3 strands of ????? copper for each conductor.

This looks similar to that in the picture below. This particular cable dates from before 1971. Therefore this cable is at least 49 years old!

This type of cable is nearing the end of it’s life. IF you are inspecting an installation with this type of cable, be sure to pay particular attention to both insulation resistance values & also loose conductors as the conductor becomes softer.

Estimated Age Of Wiring System - At Least 49 Years!!
Estimated Age Of Wiring System – At Least 49 Years!!

Earthing & Bonding

Both the earthing & the bonding can give some clues when dating old electrics.

Fuse Board / Consumer Unit

When wanting to know the age of older electrical systems, it is possible to gain some input from the age of the fuse board / consumer unit.

It should be taken into account, however, that the main board can often have been upgraded since the installation of the actual wiring system.

For this reason you should never rely solely on this as an accurate method of dating the electrics.

Estimated Age Of Wiring System - Between 30-40 years
Estimated Age Of Wiring System – Between 30-40 years

Main Service Head

This part of the installation is possibly the least reliable in terms of dating the age of the wiring system.

Main service heads can have been in place for many, many years and still provide a reliable service.

Conversely, if there has been an issue with the supply network, the distribution network owner (DNO) can replace the service head with a newer model without any of the installation having been altered.

For this reason alone, we don’t recommend using this when estimating the age.

For reference purposes however, we will give an idea of the age of certain types of main service head

Double Pole Fused, Cast Iron Service Head – fitted approx 1940s

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