Size of Strands in Stranded Cable, and..

[JFletcher]

I've been looking, to no avail, to find a chart that lists the strand size in stranded cable, from 8ga to 500MCM. All mfg list count but I dont see a size. Would the strands be a standard size?

For example, southwire 250 to 500MCM all has 37 strands. What size would they be tho? There are 5 cables in that range (250, 300, 350, 400 and 500MCM) - would they be made of 37 10,11,12,13,14ga, metric sizes???

Also, 500MCM is good for 430A at 90C. Assuming the strands are 10ga wire, why is there such a severe derating over 37 separate 10ga wires? If you had 37 10ga CCC in a conduit, you'd be at 40% derating. 37 x 40 = 1480 x .4 = 592A.

eta: no sooner I post this thread Ifound a chart that lists strand size:

http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet46***

37 116 mil wires. By this chart:

http://www.engineeringtoolbox.com/awg-wire-gauge-circular-mils-d_819.html

that puts it larger than #10, yes?

*** where are those ampacities coming from?

 

[Electric-Light]

*** where are those ampacities coming from?

" +Ampacity based on 75°C conductor temperature; 25°C ambient temperature; 2 ft./sec. wind in sun."

Wire has much better cooling when its open to the air all the way around with no thermally insulating jacket around.
It's got nothing to do with rules or codes. It's got to do with amps it takes to bring the conductor to 75C when its 25C outside in a 2ft/sec breeze.

 

[iwire]

Also, 500MCM is good for 430A at 90C. Assuming the strands are 10ga wire, why is there such a severe derating over 37 separate 10ga wires? If you had 37 10ga CCC in a conduit, you'd be at 40% derating. 37 x 40 = 1480 x .4 = 592A.

Because as the bundle of strands gets bigger the strands on the inside cannot shed the heat like they used to and this causes the entire conductor to run hotter.

It is often cheaper to run parallel conductors for this reason.

I would not call it derating as don't call that 500 kcmil "10AWG x 37" conductor.

I am sure someone will mention skin effect but at 60 Hz it's effects are minimal in the wire sizes we use.

 

[jumper]

I've been looking, to no avail, to find a chart that lists the strand size in stranded cable, from 8ga to 500MCM. All mfg list count but I dont see a size. Would the strands be a standard size?

Table 8, Chapter 9 NEC

 

[jaylectricity]

This may be silly, but using the area of the large conductor, dividing by the number of strands, couldn't you get the area of each strand, then use the same table to see which gauge wire is reasonably close to that area?

 

[Smart $]

This may be silly, but using the area of the large conductor, dividing by the number of strands, couldn't you get the area of each strand, then use the same table to see which gauge wire is reasonably close to that area?

Not silly at all.

 

[jaylectricity]

Not silly at all.

I may have been using "silly" ironically. Or I may have been wondering if I had found the super secret calculation to solve problems.

Or maybe I just wondered if OP had thought of it that way.

 

[Smart $]

I may have been using "silly" ironically. Or I may have been wondering if I had found the super secret calculation to solve problems.

Or maybe I just wondered if OP had thought of it that way.

Well if you don't know what you or the OP were thinking, I certainly don't.

I may have said excessive if regarding after someone leaked Chapter 9 Table 8 lists strand count and strand diameter... but regarding your suggested action before that point in time I guessed "not silly". :thumbsup:

 

[Cow]

As soon as you realize ampacities and correction factors are all based on the ability to shed heat, the NEC starts to make more sense. At least in that regard.