Selective Coordination, as described in the 2005 National Electric Code® (NEC®) Article 100, states "Localization of an overcurrent condition to restrict outages to the circuit or equipment affected, accomplished by the choice of overcurrent protective devices and their ratings or settings." Essentially in a selectively coordinated system only the breaker directly supplying the overloaded/faulted part of the system will open, thus allowing the rest of the system to operate. Since the choice of the overcurrent protective device, their ratings or settings is a task of the design professional, a better understanding of the options and choices is required.

An understanding of protective devices, their operation, selection and settings in relationship to selective coordination is essential for the design engineer in order to properly design a system which meets 2005 requirements. In all cases, each selected low voltage circuit breakers must have a voltage rating and interrupting capacity equal to or greater than the system voltage and available fault current at its' point of application in the electrical distribution system. UL listed series ratings cannot be utilized in a selectively coordinated system, this applies for both circuit breakers in series or a fuse in series with a circuit breaker. Both fuses and low-voltage circuit breakers, if properly selected, can be utilized to meet NEC requirements for selective coordination.

Eaton supports the intent of the selective coordination requirements of the NEC. To achieve a balanced safe and reliable system, the Licensed Professional Engineer is best qualified to optimize selective coordination and arc flash protection as far as practicable, including Articles mandated by the current NEC and meeting NFPA 70E requirements. Selective Coordination in the range of 0.1 seconds and above is widely considered "as far as practicable."

Eaton has developed tools to help you:

1. Quickly and easily select main and branch breaker combination that have been pre-tested and certified to assure selective coordination.
2. Confirm that a system you have designed is Selectively Coordinated.

The tools are described below and can be easily accessed via the links in the "Training and Tools" section on this page.

Selective Coordination Breaker Application Chart
These selective coordination tables show coordination between specific line side and load side circuit breakers, for various maximum values of fault current at the load side breaker. These tables are based on circuit breaker test data. It should be noted, that the level of load side fault current at which two breakers will selectively coordinate is significantly higher utilizing manufacturer’s test data than would be indicated by circuit breaker timecurrent curves.

Selective Coordination Breaker Application In Panelboards
This guide is designed to facilitate the selection of Eaton lighting and power panelboards, Types PRL1a, PRL2a, PRL3a and PRL4B using molded case circuit breakers which attain full selective coordination. This document utilizes information contained in the document above, "Selective Coordination Breaker Application Chart". The selective coordination values shown are based on Eaton test data.

Selective Coordination Chart for MCCBs Fed By Distribution Transformers
This chart shows coordination between transformers, secondary main breakers and feeder breakers. To design a system using this chart, a design engineer simply needs to know the KVA and impedance of the transformer and can then select a secondary main and coordinated branch breaker based on load requirements.

Selective Coordination Calculator
The calculator determines if a system is selectively coordinated based on specific parameter entered by the user. Parameters include fault current or transformer KVA, conductor length and secondary main breaker. By changing the parameters, a design engineer can determine if different systems are coordinated and if not, can alter those parameters to create a coordinated system.