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Balancing Loads on Switchboards, UPSs, and Other One-Line Devices

Wednesday, July 16th, 2014

Problem

You have a three-phase one-line device that is not a panel or a meter center. It has multiple single-phase loads on it. All the loads start on phase A, resulting in a very unbalanced panel.

Solution

In the Circuiting dialog, change the Starting Phase for some of the circuits on the one-line device.

This works for:

  • Switchboards
  • Transformers
  • Wireways
  • Bus Gutters / Bus Ducts
  • Enclosed Breakers / Disconnects
  • UPSs
  • Motor Control Centers
  • Generators
  • Transfer Switches

Why? (The Difference Between Panels and Switchboards)

The circuits on panels and meter centers rotate their starting phase automatically. Circuit 1 is on phase A, circuit 3 is on phase B, circuit 5 is on phase C, and so on. If you connect single-phase loads, they end up nicely balanced on the panel.

All other one-line devices, such as switchboards, do not rotate their starting phases. All circuits start on phase A. If you only use three-phase loads, this works fine and everything ends up balanced.

However, when you use single-phase loads, they all end up on phase A. You have to manually move some of the loads to a different phase to balance the panel.

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