Information

ELECTRICAL SOLUTIONS
C1.46
B2.
Cable
Accessories
C1.
Wiring
Duct
C3.
Abrasion
Protection
C4.
Cable
Management
D1.
Terminals
D2.
Power
Connectors
E1.
Labeling
Systems
E2.
Labels
E3.
Pre-Printed
& Write-On
Markers
F.
Index
B3.
Stainless
Steel Ties
C2.
Surface
Raceway
E5.
Lockout/
Tagout
& Safety
Solutions
B1.
Cable Ties
A.
System
Overview
D3.
Grounding
Connectors
E4.
Permanent
Identification
Wirefill Formula
General Formula
Panduit Wiring Duct wirefills are calculated using the following general formula:
Why use a 50% Wirefill?
As specified in NFPA79-2007 section 13.5.2, Percentage Fills of Raceways (Ducts), a 50% wirefill is given as
the maximum wirefill capacity in all Panduit Wiring Ducts. This helps ensure general safe wiring practices
are followed. In actual practice, a 50% wirefill is the maximum amount of wiring the duct can hold given the
additional airspace created between cables by non-uniform cable shapes, cable interlacing, and cable
packing factors.
Since we use the outer
channel dimensions in
our calculation, we
make an adjustment in
our formula for the
thickness of material
and for design elements
that extend inside
the channel.
In our wirefill formula an
adjustment is made to the
channel internal area to
account for “unusable” air
space that will be present
between cables when placed
in the channel. Our formula
assumes a uniform close
packed or high-density
cable arrangement
(see diagram) (Note1).
What is the Usable Duct Area?
The usable area we define as the calculation of internal area that can be occupied by wires or cables.
Wire Area
The wire area formula is converted to allow calculation using the cable diameter:
Formula Derivation
Inserting the elements from above into the
general formula results in the following:
Note: When calculating wirefill capacity using the above formula, variables W, H, and D must be expressed in
same units (i.e. mm or inches).
1
This calculation does not account for additional airspace created between cables by non-uniform cable shapes, cable interlacing, and cable packing factors.
2
The resulting formula is used for all Panduit flush cover ducts, this excludes type NE duct which has a different profile design that results in a
divisor of 2.0 x D
2
(rather than 1.75 x D
2
as shown here) and type H and HS wiring duct with a profile design that results in a divisor of 1.85 x D
2
and
corner wiring duct which uses calculated internal area and a divisor of 2.0 x D
2
.
Simplifying this formula results in the formula
used for wirefill calculation (Note 2):
Considering these factors, the usable duct area is equal to an average of 90% of the nominal area,
or (W x H) x .90.
Calculation of Internal Area Air Space Allotment