How to calculate diameter of cable to calculate cable tray fill?

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Pok3r

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Example:
A cable tray with a width of 2in by 6in has a 12 sq inch of area.
Per NEC 50% rule 12/2= 6 Sq inch space for cables.
Cat 5e cable = .21 in (DIA) = 3.14(.21)2/4=.04 sq in


Can someone tell me what am I missing where is the 2/4 coming for and how is the answer .04.

(To complete)

6 sq in. / .04 sq inch = 150 cables


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A=1/4*3.14*(.21*.21)=.035


Google has a good calculator search for this "area of a circle with diameter"
 
Pok3r said:
Example:
A cable tray with a width of 2in by 6in has a 12 sq inch of area.
Per NEC 50% rule 12/2= 6 Sq inch space for cables.
Cat 5e cable = .21 in (DIA) = 3.14(.21)2/4=.04 sq in


Can someone tell me what am I missing where is the 2/4 coming for and how is the answer .04.

(To complete)

6 sq in. / .04 sq inch = 150 cables


Sent from my iPhone using Tapatalk
Click to expand...

the area of a circle is pi *radius squared, so in your case, the diameter divided by 2 to get the radius and then squared. I actually come up with .0346 square inches as the radius, and that is quite a few more cable.
 
Pok3r said:
...
Cat 5e cable = .21 in (DIA) = 3.14(.21)2/4=.04 sq in

Can someone tell me what am I missing where is the 2/4 coming for and how is the answer .04.
...
Sent from my iPhone using Tapatalk
Click to expand...

What that is trying to say is to take the diameter of 0.21 and square it, multiply that result by 3.14 and then divide that number by 4. When you do that you really get 0.0346185 and it appears they rounded that to 0.04.
 
Pok3r said:
Example:
A cable tray with a width of 2in by 6in has a 12 sq inch of area.
Per NEC 50% rule 12/2= 6 Sq inch space for cables.
Cat 5e cable = .21 in (DIA) = 3.14(.21)2/4=.04 sq in


Can someone tell me what am I missing where is the 2/4 coming for and how is the answer .04.

(To complete)

6 sq in. / .04 sq inch = 150 cables


Sent from my iPhone using Tapatalk
Click to expand...

It's not really "2/4", that's just a bad rendering of the actual formula. It was probably copy and pasted from a text, in a way that failed to render the superscript notation of d^2. Area of a circle given diameter d, is pi*d^2/4. First you square the d (written properly as d^2), then multiply by pi, then divide by 4.
 
I don't understand where a 4 comes in to this. A
=
π

r
2







since diameter is supplied R=D/2
=3.1416*(.21/2)2

Which equals .0346
 
Pie are square. My mneumonic from the fourth or fifth grade.

I'm calling typo. ;)

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