Knowing the difference between imperial cable and metric?

armeg
Advertise with us
shop deals on amazon
Shop deals on ebay
Talk Electrician Forum

Help Support Talk Electrician Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
HappyHippyDad

HappyHippyDad

Well-known member
Joined
Aug 30, 2024
Messages
83
Reaction score
102
Location
Stroud
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).
 
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).
Click to expand...
 

Attachments

  • wdpPZ5YfVhrm9KLIh6QVtv5UFl0MEreXVg.png
    wdpPZ5YfVhrm9KLIh6QVtv5UFl0MEreXVg.png
    58.1 KB
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
 
Last edited:
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.
 
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
 
Last edited:
If I found a lighting circuit VIR in sliptube conduit. I would struggle to give it a satisfactory even before testing.
 
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.
Click to expand...
What tolerance do you give for the low side of acceptable?
This isn't something that needs Coding 3.6 meg ohm is fine.
 
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.
Click to expand...
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).
 
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
Click to expand...

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.
Click to expand...
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?
 
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.
 
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?
Click to expand...
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.
 
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.
 

Similar threads

boltonsparky
Cable CSA
Replies
5
Views
733
boltonsparky
boltonsparky
roys
Old conduit house wiring.
Replies
5
Views
1K
Evans Electric
Evans Electric
Social Integrator
  • Locked
Voltimum - 18th edition wiring regulations are now mandatory. Are you compliant?
Replies
9
Views
2K
SPECIAL LOCATION
SPECIAL LOCATION

Latest posts

Top