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CHAPTER 10 The Service Entrance Objectives • List the components of the service entrance. • List service drop clearances specified in the NEC. • List eight basic guidelines when locating a residential service entrance. • Calculate the size of service entrance needed based on the power needs of the dwelling. • Select proper conductors and components for the service entrance. • Size and install conductors between the meter socket, main disconnect, and service panel. • Provide proper grounding for a service entrance. • Explain the purpose of a step-down transformer and indicate where it is used. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Service Entrance • All conductors, devices, and fittings that carry electricity from power company’s transformer to the consumer • Service entrance components: – – – – – Service entrance conductors Meter socket, pan, or enclosure Service entrance panel Grounding system Fittings, fasteners, and hardware © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Service Entrance Location • Service drop—Overhead service entrance conductors (OSHA) © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Service Entrance Location (cont.) • Service lateral—Buried service entrance conductors © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Selecting Service Entrance Location • Underground service conductors installed in a straight line • Service conductors should be kept as short as practical to minimize voltage drop • Service conductors must enter building as near as possible to the service panel • Service disconnect must be at or near point of entry © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Selecting Service Entrance Location (cont.) • Service panel must be located in a central and accessible area • Service equipment must be protected from physical damage, water, and dust • Service equipment cannot be placed in bathrooms, storerooms, closets, or damp basements © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Number of Services • Generally, a structure can have only one service • Some exceptions: To supply fire pump or emergency system To supply a large load demand Large structures Service from a generator or solar photovoltaic source – Multiple voltage/phase requirements – – – – © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Service Disconnects • For multiple occupancies buildings, a maximum of six disconnects can be connected to a single service drop or lateral © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Code Alert • Sizing Service Entrance Conductors Reprinted with permission from NFPA 70-2011, National Electrical Code, Copyright 2010, National Fire Protection Association, Quincy, MA 02169. This reprinted material is not the complete and official position of the NFPA on the referenced subject, which is represented only by the standard in its entirety. © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Service Drop • • • • • • Service drop mast Insulator Service head Drip loop Meter socket Meter © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Temporary Wiring • Provides electrical power during construction © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Temporary Wiring (cont.) • Installation requirements: Locate in a safe place Keep conductors overhead if possible All receptacles require GFCI protection Protect wiring from physical damage Lamps require protective covers Weatherproof housings required when exposed to weather – Inspect frequently – – – – – – © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Service Disconnect • Service equipment must include a disconnect that disconnects service from building’s wiring system • Common types: – Main disconnect switch – Main circuit breaker in service panel © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Service Grounding • Grounded (neutral) service conductor connected to neutral bus bar in service panel • Neutral bus bar is connected to grounding bus bar • Grounding bus bar is connected to grounding electrode © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Grounding Electrode Conductor • Connects grounding bus bar in service panel to grounding electrode © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Above-Roof Clearances (OSHA) © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Above-Grade Clearances © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Building Opening Clearances © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Transformers • Convert voltage and current • Primary winding • Secondary winding © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Transformer Equations Voltage of Primary Turns of Primary Voltage of Secondary Turns of Secondary Primary Voltage Secondary Voltage Secondary Current Primary Current © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Transformer Example • Primary: 12 V, 20 A • Secondary: 120 V • Find secondary current Primary Voltage Secondary Voltage Secondary Current Primary Current 12 V 120 V x 20 A 120x 12 20 x 12 20 240 2A 120 120 © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Transformer Types • Step-up transformer—Voltage increases from primary to secondary • Step-down transformer—Voltage decreases from primary to secondary © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Phases • Single-phase • Two-phase • Three-phase © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Single-Phase, Three-Wire System © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Three-Phase, Four-Wire Wye System © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only. Three-Phase, Four-Wire Delta System © Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only.