21 Conduit Fill

The numbering system can also be used to determine how many wires will need to be pulled through the conduit to connect each device properly.

Consider the following control circuit and proposed conduit layout:

A schematic diagram of a jog circuit utilizing a control relay and the proposed layout of the installation

If this is the proposed physical layout of the equipment, how many wires must be pulled through each piece of conduit?

Conduits “A” and “E” will have only the 3-phase power conductors in them. Conduit “D” will have the three power conductors as well as several control conductors. It is permissible for control conductors to share a conduit with power conductors provided their insulations share the same voltage and temperature ratings.

To determine how many control circuit conductors will need to be pulled through each conduit, we apply the numbering system.

First, number the wires in the schematic. Each point that is electrically common gets the same number. Jump up to the next number each time you go through a device or load.

A numbered schematic diagram

Once the schematic diagram is complete, transfer the numbers of each device to their corresponding location in the wiring diagram. Each point that has the same number needs a wire connecting them.

Conduit fill determined in the wiring diagram with numbers transferred from the schematic diagram

Knowing the total number of wires to pull through a complicated run of the conduit is critical because adding wires afterwards can be impractical and difficult.



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Basic Motor Control Copyright © 2020 by Aaron Lee and Chad Flinn is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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