5424Ch07 - FM 5-424 CHAPTER 7 Switches and Fuses Manual and...

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FM 5-424 Switches and Fuses 7-1 CHAPTER 7 Switches and Fuses Manual and automatic switches are used to open and close circuits. They must be designed to carry their rated current continuously without overheating and must have clearances and insulation for the normal voltage of the circuit. Fuses and circuit breakers provide a simple, comparatively inexpensive method of automatic overcurrent protection, as well as a means of controlling the location of breakdowns. DISCONNECTS Disconnect switches are generally used in a primary circuit where opening the circuit is necessary under voltage with little or no load current. They must interrupt only the charging or exiting current of lines or appa- ratus connected. These switches are ordi- narily used to disconnect branch lines, off- circuit breakers, and transformers where the load current may otherwise be broken. TYPES Disconnect switches are available in various types, ratings, and classes. The switch shown in Figure 7-1 is used at switch struc- tures and out on the line. If the mounting height is not too great, the switch can be operated from the ground with a long- handled switch stick. The switches shown in Figure 7-2, page 7-2, are used for line sec- tionalizing. They are generally installed on the crossarms carrying the primary circuit and are operated by a switch stick that can be fastened to the lineman's belt. BYPASS SWITCHES Bypass switches may be used at booster and regulator installations to provide a quick, reliable means of taking such apparatus in and out of service without de-energizing the feeder circuits and to prevent winding burn- outs from open-circuit windings. Single crossarm hanger 7,500-V insulator unit Double crossarm hanger 15,000-V insulator unit Disconnect switch Figure 7-1. Open-type disconnect switch and components
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FM 5-424 7-2 Switches and Fuses Porcelain-housed, dead-hinge disconnect switch ″×4 ¼ to 4″×5″ crossarm 15 ¾ 7 ³/8 8 ¾ 5½” Porcelain-housed, quick-break disconnect switch Figure 7-2. Enclosed-type disconnect switches
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FM 5-424 Switches and Fuses 7-3 GANG-OPERATED DISCONNECTS Gang-operated disconnects are used where more than one phase of a circuit must be
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This note was uploaded on 05/21/2010 for the course ELECTRICAL Electrical taught by Professor N/a during the Spring '10 term at Open Uni..

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5424Ch07 - FM 5-424 CHAPTER 7 Switches and Fuses Manual and...

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