4mm2 twin and earth cable

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.

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.