Calcs get a bit involved when cables are stranded. if there are 7 strands, the cable assumes a hexagon layout. By measuring either the diameter of a single strand, the major diameter (across the points of the hex) or the minor diameter (across the flats) you can get the CSA from this table:
Be careful when measuring the hex diameters - it can distort and give a false reading. for that reason, I prefer to measure a single strand, but this isn't always possible without dismantling a joint.
Good table, stunlawless - I wish I'd found it before constructing my own from experience & measurements!
I'd also add that I've come across 3 strand 1.5mm^2 twin & earth cable with solid 1.0mm^2 cpc. The strand diameter is 0.8mm.
With the prevalence of smartphones and downloadable apps, I've created a simple Excel spreadsheet you can use on a PC or smartphone. As long as you have a vernier caliper for the measuements, just tap in the strand or conductor diameter, tne number of strands, and it'll give you the CSA.
I'm assuming those measurements are in old money? You may well be right. I measured the strands as being 0.79mm dia, but it's not difficult to be inaccurate at that level of resolution with hard steel jaws on soft copper!
I just find it easier to remember and use the ratio of two integers rather than a decimal to express a constant. It may be worth noting that for a given number of digits, both methods have the same accuracy. Thus the accuracy of 22/7 is in the same order as 3.14 and 355/113 as 3.14159.
But then, I was brought up in the (now forgotten) slide-rule age, the age before the electronic digital calculator age.
I just find it easier to remember and use the ratio of two integers rather than a decimal to express a constant. It may be worth noting that for a given number of digits, both methods have the same accuracy. Thus the accuracy of 22/7 is in the same order as 3.14 and 355/113 as 3.14159.
This is starting to remind me of some lectures on number theory which reside somewhere in my very dusty memory! Might I suggest that, in contexts such as the one of this thread, taking pi as 3 (or maybe 3.1) is probably quite adequate?!
So was I (and I still have several slide rules, including a cylindrical one capable of 4 digit accuracy) - but there was no need to fiddle around with these fractions - pi was almost unvariably marked on the scale of the slide rule.
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