There's nothing erroneous about that - it's a truth of very basic physics.
Anything claiming other than the 'inevitable truth' mentioned above is incorrect.
I think he's probably moved the goalposts a fair way - from 'specifications' (which one would hope and expect would be 'internally consistent') to real-world measurements, which are subject to variability (primarily manufacturing and measuring tolerances).
Well that's the rub isn't it. Nearly all real-world materials have impurities and the precise level and composition of impurities are going to affect the resistivity. So different cable manufacturers may end up with "copper" that has slightly different resistivity.
Although I'm being 'flippant' here, yes of course I know that.
The discrepancies have been discussed here but TBH it's not something I've previously given a thought to as the OSG figures have usually been very close to any measurements, yes discrepancies may exist but usually the lengths involved means they are minimal/easily described as measuring error. The test I did earlier consisted of clipping on and taking a reading of each conductor 5 times and the 5 different readings were averaged, even the red and black were slightly different and came out as 82.996 and 83.0034 metres (just realised I didn't edit that correctly, I originally typed all the test figures and all the calculation/averages) but the figures for the shorter length of 1.5mm² give a different story but I don't know whether it's the 1.5 or 1.0mm² conductor which is the wrong size.
I haven't moved any goal posts, all I've done is measure a couple of bits of cable and give the results.
It doesn't really matter where they come from as long as they work in real live situations and until now I've never had a reason to question OSG list.
Exactly. That's why I asked if anyone has come across a case where an actual manufacturer is specifying resistances of different sizes of their cables which are not exactly) inversely proportional to the CSA of the conductors in the cables.
I doubt that many of us have every bothered to spend time thinking about this, since the (various!) figures available to us are all perfectly adequate (and clearly 'close enough to the truth') for all practical purposes.
The comparison of resistances of 2.5mm² and 1.5mm² should be identical at any temperature - provided, of course, both conductors are at the same temperature.
Yes - but, as I said, you're addressing a somewhat different question/issue than the one I've been discussing, because you are talking about actual measurements of actual cables - which introduces the issues of manufacturing tolerances and measurement tolerance/error.
I think we are agreed that all the figures we've seen are perfectly adequate for practical purposes.
Thanks.
Hopefully I'm out tomorrow cable pulling (6mm² ring main) I'l try to measure a whole drum before we start, for that we will have to assume the 100m length is correct.
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