Conduit and Cable Capacity Factor Calculation

This article describes in detail the maximum number of wires that can be passed through a 16 mm by 25 mm PVC conduit pipe. It also explains in detail how the wire and pipe are calculated. It has to be calculated in electrical based on various criteria. The typical length of the conduit is three meters.  

It is only describes up-to 3 meter straight conduit capacity calculation for 20 to 32 mm conduit pipe cable factor or capability.

If the pipe is more than 3 meter long and has more than one bend, click here to read the next article to know more about cable factor or capacity.

Standard Capacity Factor in Conduits;

The cable factor is standardized for one cable 51%, two cables 31% and more than two cables 40% in three meter straight conduit.

Conduit and Cable Capacity Factor Calculation


It is important to know and adhere to the conduit fill capacity. Because many wires carrying too much current will go together, it will create enough heat to melt the vinyl or PVC insulation of the wires and create the conditions for a dangerous fire.

Cable Capacity Factor Calculation in Conduit

The Solid and stranded cable or insulated wire capacity into PVC/metal conduit pipe can be calculated in simple ways in electrical engineering. But some people still do not have a proper understanding of the subject. So after understanding this it is imperative to do the electrical wiring. So we should know cable factor and conduit factor.

PVC Conduit

Rigid polyvinyl chloride (PVC) is a plastic conduit often used in underground installations and in damp areas. This conduit is about 3 meter long and is called the female side as it has a coupling at one end. Similar to PVC plumbing pipe connections, PVC conduit pieces are permanently bonded together with PVC solvent cement. Because PVC has thicker walls than metal conduits, it can accommodate fewer wires. PVC pipes have no conductivity so it cannot able to act as a grounding conductor. 

​Use the charts below to determine the maximum number of wires (conductors) that can be placed in a conduit tube, depending on the NEC standard.

PVC or Metal Conduit Cable Capacity Factors in mm

Conduit Dia in mm Cable Capacity Factor
16 mm 290
20 mm 460
25 mm 800
32 mm 1400

Solid and Stranded Cable Factor

Type of Conductor Cross Sectional area of Conductor (mm2) Cable Capacity Factor
Solid Conductor 1.0 22
" 1.5 27
" 2.5 39
Stranded Conductor 1.5 31
" 2.5 43
" 4.0 58
" 6.0 88
"10 146

Solid or Stranded Cable Factor

Conductor Type Cross Sectional area of Conductor (mm2) Cable Capacity Factor
Solid or Stranded 1.0 16
" 1.5 22
" 2.5 30
" 4.0 43
" 6.0 58
" 10 105


In any case the pipe and wire in industrial or household electrical wiring should be selected only after choosing the right method. There are two main factors to consider: cable factor and PVC conduit factor. Also look at the factor calculation table of the wire and the pipe to know how many wires can be passed through a conduit pipe.

Let us first see how to calculate the area of the pipe and then understand the wire area factor as well.


Cable Spacing Components

To determine the size of the required conduit, the size of the cable of each size must be multiplied by the appropriate factor and compared with the total number of conductors.

Wire Capacity Calculation in PVC Conduit

E.g., no 1 - What size conduit is required for 8 Nos of 2.5 mm cables up to 3-meter straight run?

Factor of 2.5 mm Cable = 43 (From the cable factor table)

Total cable factor

Total number of cable x cable factor = 8 x 43 = 344

16 mm conduit factor is 290 (From the cable factor table), 290 < 344

So, we can’t select this conduit pipe for calculated cable factor requirement. It is therefore necessary to select the size of the adjacent conduit factor from the list.

Answer: - 20 mm and the conduit factor 460 (From the cable factor table)

Different Size Cable factor Calculation 

E.g., No 2 – Different size cable factor calculation

What size conduit is required for 6 Nos of stranded 2.5 sq mm + 6 Nos of  stranded 1.5 sq mm cables up to 3-meter straight run?

Cable factors from above mentioned table:-

2.5 mm Stranded cable factor = 43

1.5 mm Stranded cable factor = 31

1.5 mm Solid conductor factor = 27

6 x 43 = 258 + 6 x 31 =186

Total calculation of cable factor is;  258 + 186 = 444

Answer: - 20 mm conduit, because of total factor 444 is less than 20 mm conduit factor 460


I hope you have learned from this article what is the Conduit and Cable Capacity Factor Calculation. Thanks for reading this article to understand the conduit and cable capacity factor electrical wiring. Follow us our website for newly updated articles on electrical engineering and technology.

Read more to find exceeding 3 Meter length conduit capacity factor...

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