Engineering Documentation

Chapter 1 – Wiring Regulations and Specifications
Conduit Fill
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Conduit Fill
All wire must have insulation rated for the highest voltage in the conduit and must be
approved or listed for the intended application by agencies such as UL, CSA, FM, etc.
The following tables contain wire specifications. For more information, see Circuit
Classes [➙ 14] and Conduit Sharing–Class1/Class2 Separations [➙ 14] in this
chapter and Using Existing Wiring [➙ 32] in Chapter 2.
Cables per Conduit Size – Siemens Industry
Recommendation
Siemens Industry recommends a 40 percent conduit fill. Use the following table to
determine the number of cables (twisted pairs and twisted shielded pairs) per conduit
size at 40% fill. Plenum wiring can be used in place of any low voltage wiring without
changes to length. The Field Purchasing Guide lists the outside diameter for each
cable.
Conduit Fill.
Outside Diameter
1)
Quantity in Conduit at 40% Fill
1/2"
(12.7 mm)
3/4"
(19.1 mm)
1"
(25.4 mm)
1 1/4"
(31.8 mm)
1 1/2"
(38.1 mm)
2"
(50.8 mm)
0.325" (8.255 mm) 1 3 4 7 10 16
0.3" (7.62 mm) 2 3 5 8 12 19
0.25" (6.35 mm) 2 4 7 12 17 27
0.225" (5.715 mm) 3 5 9 15 20 34
0.2" (5.08 mm) 4 7 11 19 26 43
0.175" (4.445 mm) 5 9 14 25 34 56
0.15" (3.81 mm) 7 12 20 34 46 76
0.125" (3.175 mm) 10 17 28 49 66 109
1)
Plenum-rated cable generally has a smaller diameter than equivalent non-plenum types. Check specific product tables in this
chapter for specific applications where plenum cable must be used in conduit.
Cables per Conduit Size—NEC Requirements
NEC allowable conduit fill is 53 percent for 1 conductor, 31 percent for 2 conductors,
and 40 percent for 3 or more conductors. Use the following table to determine the
number of cables (twisted pairs and twisted shielded pairs) per conduit size in
accordance with NEC fill requirements. The Field Purchasing Guide lists the outside
diameter for each cable.
● Protective signaling circuits cannot share conduit with any other circuits.
● Class 2 circuits cannot share conduit with Class 1 circuits except as noted.