wire duct sizing Sunday, April 16th, 2006 @ 2:34 am

Q.		i would like to design panel acccording to I/O counts and wires .can u suggest the sizing & selection of ducts ,and how amny condoctors it can carry for different conductor sizes.

A.		Thank you for an excellent question. Sizing the wiring duct to be used can be difficult to determine. Most wiring duct manufacturers do typically publish the wire fill of each channel for common wire types in their catalog for basic reference. However below are some additional calculations you may employ to help you get close to the optimal size(s) faster. Please also note that if you are not looking forward to doing these calculations yourself a pre-configured spreadsheet is available for download from the Panduit website at the following link. As specified in NFPA79-2002 section 14.5.2, Percentage Fills of Raceways (Ducts), a wire fill may not exceed 50% of the available internal cross sectional area of the channel. To determine suitable duct sizes based on the wires you have, use the following formula to compare to the nominal area of (for example) a Panduit wiring duct channel: Comparison Area = 2.23 x Wire Area . (Wire Area = PIr2 x total # of wires.) For multiple wire types and sizes you will need to sum the comparison area from each wire type or determine the average wire O.D. with the following formula: Sum of (# of wire1 x wire1 O.D.) + (# of wire2 x wire2 O.D.)/total # of wires Choose wiring duct sizes with a nominal cross sectional area that is greater than the comparison area you calculated above. Duct width x duct height = nominal cross sectional area. To do the opposite and determine the wire fill of an already known duct size use the following formula for Panduit’s Flush Cover Duct: Duct Width x Duct Height / 1.75 x D2 (D = Wire O.D. and 2 = squared)