Whats this cable?

[aaron1987]

- the requirement to meet for cable manufacturers is the electrical resistance. The actual size of the conductor is not a requirement.
So you can get conductors which will not equate to exactly 2.5sqmm in size but still meet the requirements of a 2.5sqmm conductor.

I don't understand that. If the material really is copper then resistance (per unit length) and cross-sectional area are directly related. So, if it's copper and not 2.5 mm², then it can't have the resistance (per unit length) that it would have if it were 2.5 mm² copper.

Kind Regards, John

Yes I think your right john - but if you do the maths behind it the max resistance requirements of cable are actually higher than if you calculated it out using coppers resistivity. For example 1.5sqmm if calculated equals about 11.33 ohm/km and the Max resistance for 1.5sqmm cable in British standard is 12.1 ohm/km.
Don't ask me why! But interesting none then less

Following on from this if you have a 1.69mm like the original post - this would fail to meet the resistance requirement - so best to get rid I think!

 

[JohnW2]

Yes I think your right john - but if you do the maths behind it the max resistance requirements of cable are actually higher than if you calculated it out using coppers resistivity. For example 1.5sqmm if calculated equals about 11.33 ohm/km and the Max resistance for 1.5sqmm cable in British standard is 12.1 ohm/km. Don't ask me why! But interesting none then less

Two possibilities come immediately to mind. Firstly, are you sure you have done your calculation at the same temperature as the Standard has used for its quoted figures? Secondly, I imagine that, unless it's 100% pure, there will be 'copper and copper', undoubtedly with different resistivities, even at the same temperature.

Kind Regards, John

 

[aaron1987]

Yes I think your right john - but if you do the maths behind it the max resistance requirements of cable are actually higher than if you calculated it out using coppers resistivity. For example 1.5sqmm if calculated equals about 11.33 ohm/km and the Max resistance for 1.5sqmm cable in British standard is 12.1 ohm/km. Don't ask me why! But interesting none then less

Two possibilities come immediately to mind. Firstly, are you sure you have done your calculation at the same temperature as the Standard has used for its quoted figures? Secondly, I imagine that, unless it's 100% pure, there will be 'copper and copper', undoubtedly with different resistivities, even at the same temperature.

Kind Regards, John

Temperature was based on 20 degrees as per standard.
Again I think your right with the 100% pure bit but I believe copper in cable is almost 100% pure.
Copper resistivity is 1.678 x10-8 ohm/m.
Resistance = (resistivity x length) / CSA.

I think we've well and truely deviated from original question but its still interesting lol

I've found a link to an online calculator I'm case you want to have a play with some figures
http://chemandy.com/calculators/round-wire-resistance-calculator.htm

And there is also a link to requiremtns for cable Max resistance here too
https://www.tlc-direct.co.uk/Book/5.3.6.htm

 

[ban-all-sheds]

It seems very unlikely that a manufacturing error would result in both L/N and earth conductors being appreciably under-size.

No, but a cynical manufacturing con might well.

 

[Simon35]

what colour cores, sounds more like its fit for scrap, is white T and E even still made

White t + e is lsf variety and readily available.

 

[JohnW2]

Temperature was based on 20 degrees as per standard. Again I think your right with the 100% pure bit but I believe copper in cable is almost 100% pure. Copper resistivity is 1.678 x10-8 ohm/m.

Per the seemingly fairly authoritative source I'm looking at, the resistivity of pure (annealed) copper at 20°C is 1.724 x 10^-8 Ω.m (not Ω/m).

And there is also a link to requiremtns for cable Max resistance here too
https://www.tlc-direct.co.uk/Book/5.3.6.htm

That's nothing to do with maximum resistance requirements for cables. It is an extract from an obsolete version of the Wiring Regulations (BS7671) indicating typical resistance figures for use by electricians for calculations.

Kind Regards, John

 

[aaron1987]

Temperature was based on 20 degrees as per standard. Again I think your right with the 100% pure bit but I believe copper in cable is almost 100% pure. Copper resistivity is 1.678 x10-8 ohm/m.

Per the seemingly fairly authoritative source I'm looking at, the resistivity of pure (annealed) copper at 20°C is 1.724 x 10^-8 Ω.m (not Ω/m).

And there is also a link to requiremtns for cable Max resistance here too
https://www.tlc-direct.co.uk/Book/5.3.6.htm

That's nothing to do with maximum resistance requirements for cables. It is an extract from an obsolete version of the Wiring Regulations (BS7671) indicating typical resistance figures used by electricians for calculations.

Kind Regards, John

Even using the 1.724 figure it doesn't add up correctly.
And those resistance figures are the figures for the relevant conductors as per the British standard - that was just the best link I could find to clearly show the figures.

 

[EFLImpudence]

If the recognised resistance value for 10mm² is 1.83mΩ/m, shouldn't the Ω.m be 1.83x10^-8 ?

Edit - Left out the m, sorry

 

[ban-all-sheds]

Per the seemingly fairly authoritative source I'm looking at, the resistivity of pure (annealed) copper at 20°C is 1.724 x 10^-8 Ω.m (not Ω/m).

1.678 seems to be the figure in a number of other authoritative sources...

https://en.wikipedia.org/wiki/Electrical_resistivities_of_the_elements_(data_page)

That's nothing to do with maximum resistance requirements for cables. It is an extract from an obsolete version of the Wiring Regulations (BS7671) indicating typical resistance figures for use by electricians for calculations.

At 70°C.

 

[ban-all-sheds]

If the recognised resistance value for 10mm² is 1.83Ω/m,

It can't be - that figure is out by a factor of 1000.

Have you found somewhere quoting 1.83mΩ/m? Or does it say 1.83Ω/km?

shouldn't the Ω.m be 1.83x10^-8 ?

Does the website/document where you found 1.83mΩ/m list a resistivity value?

 

[DaveHerns]

Is it worth taking a chance using this suspect cable ? Get some from a reputable supplier and scrap what you have so no-one else finds it

 

[EFLImpudence]

Have you found somewhere quoting 1.83mΩ/m?

Yes, sorry. It should of course be 1.83mΩ/m.

Just from the normal resistance values used for calculations.

 

[JohnW2]

Even using the 1.724 figure it doesn't add up correctly.

I agree, but it goes some way to eliminating the inconsistency you were mentioning.

And those resistance figures are the figures for the relevant conductors as per the British standard - that was just the best link I could find to clearly show the figures.

I'm really not sure what "British Standard" you are talking about - as I said, BS7671 is not a standard for cables. If a standard defines the material, and if the resistivity of that material is known, then there would be no need for it to define ('maximum', or 'minimum', or average, or whatever) resistivity for cables of various CSAs, since those figures would follow automatically from CSA and resistivity - and, has been said, cables are made, sold and labelled by CSA, not resistivity. A British Standard cannot change physics!

Kind Regards, John

 

[JohnW2]

Per the seemingly fairly authoritative source I'm looking at, the resistivity of pure (annealed) copper at 20°C is 1.724 x 10^-8 Ω.m (not Ω/m).

1.678 seems to be the figure in a number of other authoritative sources... https://en.wikipedia.org/wiki/Electrical_resistivities_of_the_elements_(data_page)

Fair enough. Most sources only give a figure rounded to 1.7, which obviously encompasses both of the figure we're talking about. The 1.724 figure was one of the few higher precision figure I found - but, judging by the Wikipedia table, it could be the figure for 27°C, rather than 20°C

That's nothing to do with maximum resistance requirements for cables. It is an extract from an obsolete version of the Wiring Regulations (BS7671) indicating typical resistance figures for use by electricians for calculations.

At 70°C.

The Table in that article presents data for 20°C, although a footnote indicates the need to multiply the tabulated figures by 1.2 (presumably to give 70°C figures)!

Kind Regards, John

 

[ban-all-sheds]

The Table in that article presents data for 20°C, although a footnote indicates the need to multiply the tabulated figures by 1.2 (presumably to give 70°C figures)!

My apologies - I didn't look at the table - I assumed (I know - feel free.. ) it was related to all the VD figures in Appendix 4 tables, which are at maximum working temperature.

But in any event....

On the white plastic coating it says..plexman- 31. -

It looks like that number means something, even if we know not wot.

//www.diynot.com/diy/threads/10mm-cable-for-electric-shower.208760/