4mm2 twin and earth cable

I assume the cores are clearly copper, the insulation is normal low temperature PVC, and you are concerned as  they show signs of overheating - what is the expected load ?

(there was a brief foray into copper coated aluminium, but thankfully that was much earlier (~ 1970-1975), and was rapidly dropped as being hard to work with and prone to sudden failure)


As far as I know there was not single core 4mm made as standard T and E, but there may have been some special. Early 1990s is quite modern era, its unlikely to be miles out.

M.

There is no signs of overheating I'm just wondering if its the insulation of the cables that is greater in diameter. That's why I am going to measure the copper cores and also compare to some 2.5mm2 cable. Just seems that if they are 2.5mm2 the radials have been on a 32a MCB all this time.

 Regarding the circuit loading one mcb feeds 6 sockets but the loading is mainly TV's etc . the other mcb feeds the kitchen 5 outlets feeding Fridge, washing machine, toaster etc. I might just change to 20A mcb.

Thanks for your comments

If there are no signs of damage or overheating, why are you "going to change" an MCB. You are doing an EICR are you? Why have you started the inspection before you start the EICR? So you are coding this cable as a C1 and it is so dangerous that immediate action is required. Good call!


I am getting very cross about this because this is exactly the problem with people carrying out EICRs. You are not sufficiently familiar to be able to identify the size immediately. Your manufacture date must be incorrect, but the colours don't matter. It might be imperial and a single version of 7/.036. You cannot decide if this is correctly sized without measuring, and you admit that the insulation may not match the modern cable with which you are presumably comparing it. What are you going to report if the size is 3.763mm²? You have not got the measuring instrument to hand, is it accurate enough to measure the size anyway? What is impressed into the sheath, if anything? Where did you examine the cable, was it inside the CU? You need to examine a metre of so for markings, but you should know that. It doesn't actually matter if there are no markings, but they provide clues. Even if it is 2.5 there is no justification for your action, and I assume you have not contacted the customer for whom you are only carrying out a report. I may have to use the "C" word in a moment but am applying considerable constraint.


Why have you posted this anyway, there is no "answer" to your question because the answer is "quite possibly", and not definitive, but Mike has done his best. There is another note too, the cross section of cables is nominal, the actual conductor size is chosen by a manufacturer to match a resistance specification, so the measurement is not really of much use to you. "Amazingly!", most are measurably "undersized", because they are made of purer copper than the nominal specification.

I can not remember seeing or using a 4.0mm2 cable with a sold conductor, or an equivalent imperial size with sold conductor. It would be difficult to work with. Here is a link to a chart of old imperial cables that may help you.

Comparison of imperial & metric conductor sizes (daenotes.com)


Z.

In the wiring Regs. 15th Edition of 1981 a standard circuit was allowed. Table 5A applied to sockets.  to B.S. 1363.


Type A2 circuit allowed a radial circuit covering up to 50m2 area to supply sockets. It was to be fused at 30 or 32 Amps. (Cartridge fuse or circuit breaker).  The cable size was to be 4.0mm2 minimum P.V.C.  Perhaps the installer made a mistake.


Type A3 radial circuit was to cover no more than 20m2 floor area and could be wired in 2.5mm2 P.V.C. cable and fused at 20 Amps.


Cables back then were red for line and black for neutral.


Z.

Zoom

many thanks for your information it is much appreciated and helpful.

I asked the question because the cores appear larger in diameter than the 2.5mm2  cable in the next mcb. I normally carry cable information with me and examples of imperial and metric cables. 

I was asked to have a quick look at the consumer unit by a friend and that is why I asked what I thought was a reasonable query.

Don't forget 7/029 is nearly equal to 3mm

Zoom

again thanks for the information I this is why I was considering changing the mcbs.

I'll have to retreive my old regs book from the attic!

me

thanks SB

And fake cable is still about....

https://www.voltimum.co.uk/articles/counterfeiting-fighting-fake-and


Z.