Wire Amps, for give size.

[AppleJaxJap]

If I had rectangular strips of copper that were not industry standard size so no ampacity table existed for them. How would I calculate Ampacity? It seems that trying to match a specific circular mill area in the standard wire is not accurate.
I guess another way to ask is what is the ampacity of a given circular mill. When arranged in a rectangle (line a Bus) vs round ( like a wire)


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[che12345]

Deer Mr. AppleJaxJap (Electrical)(OP)3 Feb 23 03:40
"#1......All else being equal, how does the shape of a wire affect ampacity, and is their math that gets me from one shape to another?.....Now let's say you have the same 500KCMil area wire, but it was in the shape of a square, so it had more surface area....All else being equal, I would assume that the square one would be able to carry more Amps because it has 1.128x more surface area to dissipate heat...."
Yes. that the square one would be able to carry more Amps ..... This is applicable for a.c. and d.c.; based on the cooling surface.

" #2. Is that math to get me the ampacity of the square wire?.. "
Referring to my earlier post, the approximate dc current rating for flat and round bars are given in detail.
Attention: (a) for ac, the skin effect, due to frequency, size, shape and thickness etc... shall be taken into consideration. Where R[sub]f[/sub]/R[sub]0[/sub] is always > 1.0. But R[sub]60HZ[/sub]/ R[sub] 50Hz[/sub] is close to 1.
(b) the skin effect is independent of the magnitude of the current flow. There are other factors etc....
Che Kuan Yau (Singapore)

 

[che12345]

Dear Mr Deer Mr. AppleJaxJap (Electrical)(OP)3 Feb 23 03:40
1. For most cases the bar is mounted in free air, the natural cooling by Convection > radiation > conduction. For convection, the heat dissipation from the vertical surface (W[sub]v[/sub]) is about 1.29 time more efficient/effective than the heat dissipation by the horizontal surface (W[sub]h[/sub]).
2. Take a case say :
(a) [5H x 2W] i.e. vertical mount, the cooling surface by convection is W[sub]v[/sub]=2x5=10, + W[sub]h[/sub] =2 ; ignoring the less effective convection by the bottom horizontal surface.
(b) [5W x 2H] i.e. horizontal mount, the cooling surface by convection is W[sub]v[/sub]=2x2=4, + W[sub]h[/sub] =5 ; ignoring the less effective convection by the bottom horizontal surface.
From above (a) and (b), it is clear that vertically mount is preferred. Note: (W[sub]v[/sub]) is about 1.29 time more efficient/effective than W[sub]h[/sub].
Che Kuan Yau (Singapore)

 

[AppleJaxJap]

@che12345 thank you I appreciate your time and effort on this.





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[che12345]

Dear Mr AppleJaxJap (Electrical)(OP)5 Feb 23 22:55
I would like to submit the emissivity factor which had not been touched on, for your consideration.
1. Radiation (W[sub]r[/sub] ) is considered to travel in straight lines from all surfaces. It is proportional to the temperature difference to the fourth power. It is proportional to the relative emissivity (e) between the body and the surrounding.
2. Typical absolute emissivity of copper busbar: bright metal e=0.1, heavily oxidized e=0.7, dull non-metallic paint e=0.9 ....
3.For a single busbar with emissivity from e=0.1 to e=0.9 is reported to have an increase of >20% in current rating.
4. Dull non-metallic paint which are inexpensive in cost, can be manually brush/spray on at site. The thickness is immaterial. Note: dull powder coating and heat shrink on tubing are NOT cost effective and difficult to implement at side or on an existing installation.
Che Kuan Yau (Singapore)

 

[7anoter4]

See-for instance:

https://www.copper.org/applications/electrical/busbar/bus_table1.html

https://www.busbar.com/resources/copper-ampacity/

https://wiraelectrical.com/busbar-size-calculation-formula/