Knowing the difference between imperial cable and metric?

HappyHippyDad · Oct 31, 2024

I have just carried out an EICR and am trying to determine if the 1mm single stranded twin and earth is imperial or metric.

The sockets are all wired in 7/029 so are definitely imperial.

I was under the impression that solid cores came in between 1969-72 indicating metric sizing. Was there ever solid core imperial?

Basically I'm trying to discover if the lights have been rewired but it is the original wiring for the sockets. This house was built in the 50's or early 60's (I think).

7029 Dave · Oct 31, 2024

They did a 1/044 PVC imperial cable, as far as I know it never had cpc but not 100% sure.

UNG · Oct 31, 2024

CPC's on the lighting circuit would give an indication of date

7029 Dave · Oct 31, 2024

HappyHippyDad said:
I have just carried out an EICR and am trying to determine if the 1mm single stranded twin and earth is imperial or metric.

The sockets are all wired in 7/029 so are definitely imperial.

I was under the impression that solid cores came in between 1969-72 indicating metric sizing. Was there ever solid core imperial?

Basically I'm trying to discover if the lights have been rewired but it is the original wiring for the sockets. This house was built in the 50's or early 60's (I think).

Geoff1946 · Oct 31, 2024

There was the 1x0.044, as on top of your table, but I'm not sure how much it was actually used.

ExArmy · Oct 31, 2024

1/044 did come with a CPC but it's rare. pretty difficult to identify it inside a backbox on an EICR and determine if it's imperial or metric, but if you can read the sheath under the floor or in the loft if you see "BS 2004" then it's imperial
another clue is the conductor will be a silvery colour as the copper will be tinned

HappyHippyDad · Oct 31, 2024

Thanks everyone. It looks likely it's metric then, but not definitely. Thanks for the tip about the BS number @ExArmy , that will be a great help

.

The earthing on the lights is a right old mess, so I've suggested they 'consider' a full rewire, especially if they are going to get sockets rewired. It's always a difficult one when you suggest a rewire as it's never 100% needed, it can usually go on for a few more years. Still, this is exactly what I have explained to them. I have made it clear this is a suggestion (C3) and I am not classing the installation as dangerous at the moment.

Out of interest what would others code old imperial cable. IR results 3.6Mohms, so acceptable, but on the low side of acceptable. Very likely to be 50's or 60's wiring. Poorly terminated in sockets (many quite loose), strands poking out. No signs of thermal damage or green goo.

ExArmy · Oct 31, 2024

I wouldn't even code PVC imperial cable as long as IR is above 2Meg for the circuit. even if the IR was below 2Meg it's still very unlikely the cable will be the culprit and it will more likely be a jointbox or connection, or some of these loose strands you mention...
FWIW I would never recommend a rewire as long as it is at least PVC sheathed cable, unless they want a significant amount of alterations that would mean lots of joints

7029 Dave · Oct 31, 2024

If I found a lighting circuit VIR in sliptube conduit. I would struggle to give it a satisfactory even before testing.

Fleeting · Oct 31, 2024

HappyHippyDad said:
Thanks everyone. It looks likely it's metric then, but not definitely. Thanks for the tip about the BS number @ExArmy , that will be a great help.

The earthing on the lights is a right old mess, so I've suggested they 'consider' a full rewire, especially if they are going to get sockets rewired. It's always a difficult one when you suggest a rewire as it's never 100% needed, it can usually go on for a few more years. Still, this is exactly what I have explained to them. I have made it clear this is a suggestion (C3) and I am not classing the installation as dangerous at the moment.

Out of interest what would others code old imperial cable. IR results 3.6Mohms, so acceptable, but on the low side of acceptable. Very likely to be 50's or 60's wiring. Poorly terminated in sockets (many quite loose), strands poking out. No signs of thermal damage or green goo.

What tolerance do you give for the low side of acceptable?
This isn't something that needs Coding 3.6 meg ohm is fine.

binky · Oct 31, 2024

HappyHippyDad said:
Out of interest what would others code old imperial cable. IR results 3.6Mohms, so acceptable, but on the low side of acceptable. Very likely to be 50's or 60's wiring. Poorly terminated in sockets (many quite loose), strands poking out. No signs of thermal damage or green goo.

after much discussion on here some time ago, we concluded the actual regs requirement is 2Mohm for the whole installation ie IR between L Nand E busbars with the breakers in the on position (electric off of course).

HappyHippyDad · Oct 31, 2024

ExArmy said:
I wouldn't even code PVC imperial cable as long as IR is above 2Meg for the circuit. even if the IR was below 2Meg it's still very unlikely the cable will be the culprit and it will more likely be a jointbox or connection, or some of these loose strands you mention...
FWIW I would never recommend a rewire as long as it is at least PVC sheathed cable, unless they want a significant amount of alterations that would mean lots of joints

Fleeting said:
What tolerance do you give for the low side of acceptable?
This isn't something that needs Coding 3.6 meg ohm is fine.

Out of interest would you say a cable ever has a lifespan?
Let's say the imperial cable in this property is still in situ in another 50 years, and tests at 2Mohms?

Fleeting · Nov 1, 2024

The wiring in my house was on the cusp of the metric change and mine is all metric, two doors up from me they are imperial they must have used old stock. Cables in both properties are fine at 50+ years so age isn't necessarily a defining factor.

binky · Nov 1, 2024

HappyHippyDad said:
Out of interest would you say a cable ever has a lifespan?
Let's say the imperial cable in this property is still in situ in another 50 years, and tests at 2Mohms?

Cable has a lifespan dependent on use, I saw some figures for that a few years ago. A piece of 2.5mm running at full capacity 24/7 can expire in as little as 5 years.

I rewired a house that had been bombed during WW2 and fully rebuilt around 1948. The whole house was VIR, and tested as just about acceptable. The main cable runs were still in reasonable condition, try moving a socket front and the insulation just crumbled. It was only at the accessories the cable was failing, which I'm guessing is down to a little bit of heat from terminations in the accessories.

Murdoch · Nov 1, 2024

7029 Dave said:
If I found a lighting circuit VIR in sliptube conduit. I would struggle to give it a satisfactory even before testing.

Hit, nail and head springs to mind. Dating back to the 1950's its long overdue replacement. C2

7029 Dave · Nov 1, 2024

Murdoch said:
Hit, nail and head springs to mind. Dating back to the 1950's its long overdue replacement. C2

Vir in timber ducting dates back early 1900s, VIR singles in sliptube conduit was very common in the 1930s.

Murdoch · Nov 1, 2024

7029 Dave said:
Vir in timber ducting dates back early 1900s, VIR singles in sliptube conduit was very common in the 1930s.

Yes but how much is still being used?

7029 Dave · Nov 1, 2024

Murdoch said:
Yes but how much is still being used?

Hopefully not many installations still have it. I reckon it's still in service in some. ( Hope not)

binky · Nov 1, 2024

7029 Dave said:
Vir in timber ducting dates back early 1900s,

About the only thing I've not still found in use

Fleeting · Nov 1, 2024

Went to survey a large factory in Bath 20 odd years ago and in the upper stores they had PolyButyl Jute singles strung across the ceiling, what the Americans called knob and tube. I was told none of that is live but it was and powered most of the lighting all Class I with no cpc.

Knowing the difference between imperial cable and metric?

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