5424Ch01 - FM 5-424 Part One. Basic Electrical Techniques...

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FM 5-424 Fundamentals 1-1 Part One. Basic Electrical Techniques CHAPTER 1 Fundamentals This manual emphasizes the constructional aspects of electric wiring. The term phase is used when referring to the angular displacement between two or more like quantities, either alternating electromotive force (EMF) or alternat- ing current (AC). It is also used for distinguishing the different types of AC generators. For example, a machine designed to generate a single EMF wave is called a single-phase alternator , and one designed to generate two or more EMF waves is called a polyphase alternator. USAGE Power generators produce single- or three- phase voltages that can be used for electri- cal power systems at generated voltages or through transformer systems. Single-phase generators are normally used only for small lighting and single-phase motor loads. If the generated voltage is 120 volts, a two-wire system is used (see Table B-1[A], page B-1). In this situation, one conductor is grounded and the other is ungrounded, or hot. The generated single-phase voltage can be 240 volts. This voltage is normally used for larger single-phase motors. To provide power to lighting loads, the 240-volt phase is center-tapped to provide a three-wire, sin- gle-phase system (see Table B-1[B]). The center tap is the grounded neutral conduc- tor. The voltage is 120 volts from this grounded conductor to either of the two ungrounded conductors. This is half of the total phase value. The voltage between the two ungrounded conductors is 240 volts. This system provides power for both lighting and single-phase, 240-volt motors. The most common electrical system is the three-phase system. The generated EMFs are 120 degrees apart in phase. As shown in Table B-1 (C, D, E) , three-phase systems may be carried by three or four wires. If con- nected in a delta ( ), the common phase voltage is 240 volts. Some systems generate 480 or 600 volts. If the delta has a grounded center-tap neutral, then a voltage equal to half the phase voltage is available. If the phases are Y -connected, then the phase volt- age is equal to 1.73 times the phase-to-neu- tral voltage. The most common electrical system found in the military is the three- phase, four-wire, 208/120-volt system. Single-phase, three-wire systems and three- phase, four-wire systems provide voltages for both lighting and power loads. If the load between each of the three phases or between the two ungrounded conductors and their grounded center-tap neutral are equal, a balanced circuit exists. When this occurs, no current is flowing in the neutral conductor. Because of this, two ungrounded conductors and one grounded neutral may be used to
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FM 5-424 1-2 Fundamentals feed two circuits. Thus, three conductors may be used where four are normally required. Electric lamps for indoor lighting in the
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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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5424Ch01 - FM 5-424 Part One. Basic Electrical Techniques...

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