Ok its prob been asked a dozen times and explained but using the filters with AWG or wire size I get back 1000's of posts so I'll just ask again ...
Whats with AWG?
OK metric, nice and simple, its 2.5mm2 so we call it 2.5mm2, its a nice discriptive term thats easy to understand. Bigger cable bigger number, smaller cable smaller number. Simple.
Now I know the US AWG lists, and roughly what us brits would equate it to. My difficulty is in understanding the *why*. I see they picked a mid-range cable as 1 AWG .. Smaller wires go up to 18 AWG, larger wires get an *00* rating (eg 1/0 2/0 until the bigger cables are hit with the 250 Kcmil and onward numbers.
I understand the progression. I dont understand, nor can seem to find, where they pulled these numbers from. Is there a table equating actual size to the AWG number so that you can see a logical progression? Or are they just called so *just because they are* because thats they way they are produced?
I guess I am just having trouble with the *reasoning* for the AWG system. like I say I understand its progression and can equate the cable sizes, I just dont get where they pulled the size scale from.
Prob a real simple answer .. but anyways over to you.
The AWG was based on circular mil area. The starting point was #10 wire, which, when it was initiated, had a cma of 10,000 circular mils. It has since been redefined as a cma of 10,380, no, I can't really explain why. ( I do understand it has to do with more accurate measuring equipment, but....).
A more detailed explanation can be found in 2-5 of the American Electricians Handbook, it does go into an explanation of weights and resistances and how they were chosen. The Brown and Sharpe gauge is the same, and Table 2-85 gives a listing of other gauges and their equivalents.
Don't forget that metric wire sizes have been used in the U.K. only since about 1970. House wiring cables prior to that were specified as number of strands and diameter (e.g. 7/.029 = 7 strands each .029" dia.), but we also have the British SWG (Standard Wire Gauge) which works in a similar way to AWG (e.g. 32 SWG is smaller than 28 SWG).
I have read an explanation of the derivation of SWG, but it was a long time ago and I can't remember the details now.
AWG is a older way of doing the exact same thing as our metric wire sizes do. It's a geometric series where five steps makes the cross sectional area ten times larger, i.e. 6 AWG is ten times larger than 16 AWG just like 16 mm2 is ten times larger than 1.5 mm2. (Only every other size is used in AWG) Take five metric steps and you go 1.5; 2.5; 4; 6; 10; 16. The AWG does the same thing, but as the series used is an approximation the actual steps differ slightly from those used for the metric sizes. Both series use rounded numbers and the manufacturers on both sides of the Atlantic allow for fairly wide tolerances when making wires.
I know UK Imperial Sizes (Whitworth etc) and Metric. I have had the pleasure of pulling out some SWG cabling from one of the old 1940's Mills that my old company had on site. Rewired in Metric of course LOL.
I was aware of the old SWG system, but it was treated as a *good-ole-days* story lol.
The AWG system just *feels* wrong to me lol. I am trying to get used to it and slowly am. Like I say I mentally *equate* thier AWG to metric lol.
I am aware that AWG is based on the Cmil measurement. (Damm small base to take a refrence from - 1KCmil = a unit of area equal to about 0.5067 square millimeter.
So 250Kcmil cable = Roughly 127mmSQ
I guess if I figure on (Kcmil * 0.5) I'll get roughly what *I'd* call it LOL.