Series Coordination of Breakers

The SmartDesign™ feature in EasyPower finds and selects LV breakers that selectively coordinate with each other in the instantaneous trip (high short circuit current) region of the time current curves. Although the time current curves may indicate that the breakers are not coordinated in the instantaneous trip region, various manufacturers have published documents that show the extent to which a greater level of coordination is possible. These documents are based on tests and calculations. Based on the manufacturer’s data sheets, EasyPower selects the appropriate breakers in the Auto Design process so that breakers in series coordinate with each other. For coordination in the overload or short time trip regions of the breakers, it is necessary to check against the TCC plots or use EasyPower’s SmartPDC™ (Auto Coordination) feature.

The Series Coordination (of breakers) feature is integrated with SmartDesign™. If a breaker being selectively coordinated does not have the trip amps specified in the one-line data, the auto-sizing algorithms in SmartDesign™ are used to determine the size of breakers based on downstream loads and various code factor calculations.

Prerequisites for Series Coordination

Before using Series Coordination command, you will need to make sure that you have the following prerequisites.

The one-line is adequately modeled along with one source:

  • Both upstream and downstream breakers must exist.
  • If a transformer exists upstream to the breakers, the transformer size and impedance must be specified. This is the basis for calculating available short circuit currents. If there are no upstream transformers, then the utility data must be realistic.

For the design sheet specified in the options, the design sheet in the library must have the necessary data:

  • Desired breakers for the various amp values must be listed. Use manufacturer names and styles, and not “Generic.”
  • The breaker styles listed in the design sheets must have series coordination data in the breaker library.

Performing Series Coordination

Perform a series coordination, as follows:

  1. On the one-line, select the LV breakers you want.
  2. Click the arrow below the Auto Design and select Series Coordination.
  3. On the Home tab, select Window > Auto Design Report. An HTML report is displayed.

The first table in the report describes the breaker that was selected. The second table shows comments on various criteria that were used and various observations made by the program. If the program encounters problems such as lack of a solution, or exceptions, they are listed in the comments. If no solution can be found, then only the comments table is displayed.

EasyPower selects a breaker from the design sheet that selectively coordinates with the downstream breaker.

You can select a single breaker or multiple breakers. If you select multiple breakers in series, the most downstream breaker pair is coordinated first, followed by the next upstream breaker. To select multiple breakers, hold SHIFT and select the breakers.

If you select only the most downstream breaker, there are no breakers with which to coordinate. If you select the most downstream breaker and the breaker upstream to it, both breakers are chosen such that they selectively coordinate.

If a breaker has been previously specified in the one-line and the Trip Amps are defined, then that Trip Amp value is the basis for searching for a selectively coordinating breaker. If the Trip Amps have not been previously defined, the Auto Design algorithm is used to determine the Trip Amps for the breaker.

If there are multiple solutions to series coordination for any breaker, the first breaker listed in the design sheet is selected. The alternative solutions are listed in the Auto-Design report.

Bottom-up approach: Since breakers are selected to coordinate with downstream breakers, it is necessary to solve for lower level breakers first and move your way upstream.

More Information

Auto Design  
Adding Coordination Data to the Breaker Library  
Customizing the Design Template for Series Coordination

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Help was last updated on 3/22/2019