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IAEI Magazine | Author: Tim Crnko
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Tim Crnko

Tim Crnko, training and technical services manager for Cooper Bussmann, has MSEE and is a member of IAEI, IEEE, NEMA and NFPA. 


Life Safety Loads Depend on Reliable Power Systems

What matters to a person when they are in a facility that has capacity for many people and an emergency situation such as fire, flooding, storms, earthquake, explosion, or merely loss of normal utility electrical power occurs? Naturally, this depends on the situation, but the basic human instinct is to want to escape the event without physical or extreme emotional trauma. We desire safety for our family, ourselves, and others.

Selective Coordination Enforcement: Overcurrent Protective Device Basics

Merely having a higher ampere overcurrent protective device (OCPD) feeding a lower ampere overcurrent protective device does not assure a circuit is selectively coordinated. Designing a selectively coordinated system takes a knowledgeable person who is capable at the task and who has the necessary data available to select the proper devices. As an authority having jurisdiction (AHJ), evaluating whether a system is selectively coordinated does not require as much knowledge or work. However, it does require specific information which can be reviewed and interpreted. The specific information that must be provided for evaluation purposes depends on the method used to achieve selective coordination. This article covers the basics of selective coordination interpretation for fuse or circuit breaker circuits used in 600 V or less systems.

Overcurrent Protection, Part 2

Part I, which appeared in the March/April issue, provided readers with information about basic operation and basic time-current characteristics of branch-circuit, low-voltage fuses and circuit breakers. This article covers three overcurrent protective device ratings, their application in design, and NEC compliance aspects of low-voltage branch-circuit fuses and circuit breakers.

Overcurrent Protection, Part 1

This article provides readers with essential information about basic operation and basic time-current characteristics of branch-circuit-rated, low-voltage fuses and circuit breakers. These overcurrent protective devices (OCPDs) are typically used in main service disconnects, feeders and branch circuits of residential, commercial, institutional, and industrial electrical systems.

New Requirements for Selective Coordination

For certain vital circuits, the 2005 NEC requires that all overcurrent protective devices be selectively coordinated with all supply side overcurrent protective devices in the system. In addition, the definition for selective coordination has been added in Article 100. This commentary includes an overview of the requirements, what selective coordination means, the rationale for the new requirements, system requirements to comply, and the role of designers, contractors and inspectors.

Series Combination Rating Requirements

Series combination ratings are utilized to attempt to save money on some jobs. This article presents a simple checklist that can be completed by the contractor and/or designer when series rated combinations are proposed. The checklist is designed to be a single sheet that is double sided. The front side requires information for a specific series rated application. The backside provides an easy reference of general application information and provides the specific National Electrical Code requirements. In the plan review stage, the checklist provides the AHJ the necessary information to review series combinations in their specific application. During the inspection phase of the installation, the AHJ can use this checklist as a guide to confirm compliance with the design and proper installation requirements.