ICEA P-54-440 section 3.1

[Designer69]

anyone ever use ICEA P-54-440?

section 3.1 applies to derating for diameters of cables. see attached pic.

not sure what this really means: dx= cable diameter less than the calculated depth of those in tables.

if anyone has ran into this before, would appreciate some help.

thanks

 

[jeremy.zinkofsky]

Do you have the tables? That equation allows you to calculate the ampacity of cables with diameters not specified in the table that section 3.1 is referencing.
For example, if you have a #6 with a diameter that does not match the diameter for a #6 in the table.

Why are you using this standard anyway? AHJ's usually default to the NEC or IEEE for conductor ampacities.

 

[Julius Right]

I used in the past this standard. It is based on
AMPACITIES FOR CABLES IN RANDOMLY FILLED TRAY by J.Stolpe[1970] .
I have an earlier edition [of 1986] .
Formula no. 9 of Stolpe defines the permissible maximum current in a cable in a tray where all the cable present the same heat intensity Q [for a certain percent filling factor].
I=D/2sqrt(Q*pi/n/R) n=number of conductors of the same resistance[R].
D is the overall diameter of a cable.
Maintaining Q constant a more than permissible current will be obtained for larger diameter but for less diameter the same Q will be a bit conservatively so permissible.