2. 10
The Service Entrance

3. 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.

4. Objectives (cont.)
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.

5. 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

6. Service Entrance Location
Service drop—Overhead service entrance conductors
(OSHA)

7. Service Entrance Location (cont.)
Service lateral—Buried service entrance conductors
(Goodheart-Willcox Publisher)

8. 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

9. 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

10. 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

11. Service Disconnects
For multiple-occupancy buildings, a maximum of six disconnects can be connected to a single service drop or lateral
(Goodheart-Willcox Publisher)

12. Sizing Service Entrance Conductors
Copyright © 2013 NFPA

13. Service Drop Service drop mast Insulator Service head Drip loop
Meter socket
Meter
(Goodheart-Willcox Publisher)

14. Temporary Wiring Provides electrical power during construction
(Goodheart-Willcox Publisher)

15. 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

16. 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

17. 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

18. Grounding Electrode Conductor
Connects grounding bus bar in service panel to grounding electrode
(Goodheart-Willcox Publisher)

19. Above-Roof Clearances
(OSHA)

20. Above-Grade Clearances
(Goodheart-Willcox Publisher)

21. Building Opening Clearances
(Goodheart-Willcox Publisher)

22. Transformers Convert voltage and current Primary winding
Secondary winding
(Goodheart-Willcox Publisher)

23. Transformer Equations

24. Transformer Example Primary: 12 V, 20 A Secondary: 120 V
Find secondary current

25. Transformer Types
Step-up transformer—Voltage increases from primary to secondary
Step-down transformer—Voltage decreases from primary to secondary

26. Phases Single-phase Two-phase Three-phase
(Goodheart-Willcox Publisher)

27. Single-Phase, Three-Wire System
(Goodheart-Willcox Publisher)

28. Three-Phase, Four-Wire Wye System
(Goodheart-Willcox Publisher)

29. Three-Phase, Four-Wire Delta System
(Goodheart-Willcox Publisher)