5424Ch03 - FM 5-424 Part Two. Wiring Procedures CHAPTER 3...

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FM 5-424 Design and Layout 3-1 Part Two. Wiring Procedures CHAPTER 3 Design and Layout The different wiring systems in common use for civilian and armed-forces con- struction are often called cable and conduit systems. Chapters 4 and 5 cover the installation details for each of these systems. Many installation methods and procedures used in the wiring processes are common to all systems. In most wiring installations, the blueprints specify the type of wiring to be installed. If the type of wiring is not specified, the electrician must determine the installation method. In general, the type of wiring used should be similar to that installed in adjacent or nearby buildings. Section I of this chapter describes common wiring methods and procedures, and Section II describes methods for tactical or expedient wiring . Section I. Interior Wiring TYPES OF DISTRIBUTION The electrical power load in a building can- not be properly circuited until the type and voltage of the central power-distribution system is known. The voltage and the num- ber of wires from the power lines to the buildings are normally shown or specified on the blueprints. However, the electrician should check the voltage and type of distri- bution at the power-service entrance to every building in which wiring is to be done. This is especially necessary when he is altering or adding circuits. Voltage checks are usually made with an indicating voltmeter at the service-entrance switches or at the dis- tribution load centers. The type of distribu- tion is determined by a visual check of the number of wires entering the building ( Table B-1 , page B-1 ). If only two wires enter the building, the ser- vice is either DC or single-phase AC. The voltage is determined by an indicating volt- meter. When three wires enter a building from an AC distribution system, the service can be single-phase, three-phase, or two ungrounded conductors and a neutral of a three-phase system ( V-phase ). If the service is single-phase, two of the con- ductors are hot, and the third is ground. A voltmeter reading between the two hot con- ductors will be twice as great as the reading between either hot conductor and the neu- tral or ground conductor. If the service is three-phase, the voltage between any two of the conductors is the same. Normally, one of the conductors is grounded to establish a ground reference voltage for the system.
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FM 5-424 3-2 Design and Layout A V-phase system is the most common ser- vice for TO construction. The distribution system is described below. The voltage between the two hot conductors will be 1.732 times greater than the voltage between either hot conductor and the neu- tral or ground. Four-wire distribution denotes three-phase and neutral service. When tested, voltages between the neutral conductor and each of the three conductors should all be the same. The voltage readings between any two of
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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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5424Ch03 - FM 5-424 Part Two. Wiring Procedures CHAPTER 3...

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