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Electrical Protection Handbook by (NFPA) National Fire Protection Association

By (NFPA) National Fire Protection Association

Secure, effective, code-compliant electric installations are made easy with the newest booklet of this largely well known source. Like its hugely winning prior versions, the NEC 2011 Handbook combines good, thorough, research-based content material with the instruments you must construct an in-depth knowing of an important subject matters. It offers the total textual content of the up to date code rules along professional statement from code experts, delivering code cause, clarifications for brand new and up to date ideas, and sensible, real-world suggestion on easy methods to follow the code. New to the 2011 variation are articles together with first-time Article 399 on October, Overhead Conductors with over six hundred volts, first-time Article 694 on Small Wind electrical platforms, first-time Article 840 on Premises Powered Broadband Communications platforms, and extra. This profitable mix has created a beneficial reference for these in or coming into careers in electric layout, deploy, inspection, and security.

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0349 Step 5. M= Step 6. C. C. sym RMS = 49,803 + 7,216 = 57,019A LPS-RK-400SP Fuse ( fault X1) 50' - 500 kcmil Feeder Cable in Steel Conduit Fault X2 Motor Contribution System B M Fault X1 One-Line Diagram Available Utility Infinite Assumption Step 1. l. 732 Step 2. Multiplier = Step 3. C. 57 = 34,370A Step 4. f= Step 5. M= Step 6. 0348 Step 4. 1049 2 x 11,423 x 480 Step 5. M= Step 6. C. 4286 x 30,059 = 29,731A 208 Contents Index Next Previous 1Ø Short-Circuit Calculations Short-circuit calculations on a single-phase center tapped transformer system require a slightly different procedure than 3Ø faults on 3Ø systems.

6. The fuse curves represent the cutoff value of the prospective available short-circuit current under the given circuit conditions. Each type or class of fuse has its own family of let-through curves. The let-through data has been generated by actual shortcircuit tests of current-limiting fuses. It is important to understand how the curves are generated, and what circuit parameters affect the let-through curve data. Typically, there are three circuit param- eters that can affect fuse let-through performance for a given available short-circuit current.

Electrical systems can be destroyed if the overcurrent devices do not limit the short-circuit current to within the withstand rating of the system’s components. Merely matching the ampere rating of a component with the ampere rating of a protective device will not assure component protection under short-circuit conditions. In the past several years, there have been numerous reports in newspapers, magazines and insurance company files about destroyed electrical systems. Recognizing this as a serious problem to safety of life and property, much more emphasis has been placed on COMPLIANCE with THE NATIONAL ELECTRICAL CODE.

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