Consulting-Specifying Engineer - October 2007 - (Page 54)

curves of all upstream (line side) and downstream (load side) breakers to ensure that the downstream circuit breaker will open under a short-circuit condition before the upstream circuit breaker operates. To ensure that a circuit-breaker-protected system is selectively coordinated, the time-current curves must not overlap at any possible fault current. With fuses, selective coordination is achieved as long as specifiers maintain manufacturer-recommended ratios.” Zone selective interlocking uses data network communications to enable programmed trip unit settings to be altered automatically. Common place in high and medium voltage switchgear, zone selective interlocking breakers are making their way into low voltage switchgear as well. Zone selective interlocking uses data network communications between two or more compatible breaker trip units. This technology enables programmed trip unit settings to be altered automatically to respond to different fault conditions and locations. Instantaneous interruption is localized to the specific fault location, while the rest of the electrical system is maintained to provide positive coordination between circuit breakers. Coordinating electrical systems involves understanding and using timecurrent curves. “In order to plot the OCPD curves,” said James P Stroke, . PE, a consulting engineer based in Somerset, Mass., “it is necessary to either obtain the OCPD inverse time curves from the manufacturers and plot them out by hand on log paper, or use a software package that plots it all out. I print each OCPD in a different color, which really makes them stand out, and you can more easily spot overlaps and adjust accordingly. In some cases, a ‘perfect’ coordination is impossible.” Stroke also said that obtaining electrical design software could pose a problem for some. “These software packages are extremely expensive and not every engineer has these,” he said. “So, the implication is that many of the coordination studies probably just don’t get done.” The same applies to short circuit studies, he adds. “What’s really needed is an inexpensive software program for short circuit and coordination studies—either on a CD, or available online so anyone can access and use it.” “There are many choices that take place during electrical system design,” Weigel said, “and these choices should be diligently consistent with optimizing the design in a way that will also optimize arc flash safety.” more than a system—a solution. Kidde Fire Systems has the solution for your fire protection needs. Whether you’re protecting a control room, a mining vehicle, a restaurant’s kitchen or a marine engine space, Kidde Fire Systems has the knowledge and the expertise in a wide variety of industries so we can help recommend a solution for YOUR application. RISK ANALYSIS First, we’ll help you analyze the fire risk for your application. SYSTEM CONFIGURATION Next, we’ll help you select the right system for the application and design with the best configuration of detection, notification, control and suppression components from Kidde’s wide range of approved products. Start by getting your free copy of the PROTECT-SPEC cd-rom… Design System Version 3.0 PROTEC T-SPEC KCDR-002 INSTALLATION AND SERVICE Finally, Kidde has a global network of trained professionals that will install and service your Kidde system. The smart way to specify fire protection. 1-800-872-6527 ext. 2394 www.kiddefiresystems.com A UTC Fire & Security Company Setting the Standard in Fire Protection. Input #229 at csemag.com/quickResponse 54 Consulting-Specifying Engineer • OCTOBER, 2007 http://www.kiddefiresystems.com http://www.kiddefiresystems.com http://csemag.com/quickResponse

Table of Contents Feed for the Digital Edition of Consulting-Specifying Engineer - October 2007

Consulting-Specifying Engineer - October 2007 Contents On the Web In the News M/E Roundtable How To Beat the Energy Codes Professional Practices Codes & Standards A Capital Job on Engineered Buiding Systems Going Green in Data Centers Overcurrent Protection: Fuses or Breakers? Third-Party Liability Management Report New Products Product Spotlight Jobs/Classifieds Specifier's Notebook

Consulting-Specifying Engineer - October 2007

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