CHAPTER 5 INTERIOR WIRING At any Navy or advanced base, the electrical system consists of three parts: the power plant that supplies the electrical power, the distribution system that carries the electrical current from the generating station to the various buildings, and the interior wiring systems that feed the electrical power to the appliances and equipment within a building.

As defined here, interior wiring begins at the point where the distribution systems service leads are connected to the wiring from within the building and extends through each circuit of the interior wiring of the building to the last fixture installation. In this chapter, we will discuss your responsibilities in meeting various code and specification requirements and a variety of techniques for installing, repairing, and maintaining interior wiring systems. 

STANDARDS The National Electrical Code(c) (NEC(c)) is prepared and published every 3 years by the National Fire Protection Association (NFPA). You should use the latest publication and volume reference. The NEC(c) is an accepted guide for the safe installation of electrical conductors and equipment. Its purpose is to safeguard personnel and buildings and their contents from hazards arising from the use of electricity. NAVFACENGCOM recognizes the NEC(c) and uses it as its minimum standard.

How does the NEC(c) minimize the dangers mentioned above? Briefly, the NEC(c) provides the following:

Various methods of wiring and descriptions of materials Techniques for wiring designs and protection Requirements of general and special equipment Special conditions and occupancy information A variety of tables and examples for calculations The NEC(c) is a wealth of information that provides CEs with a strict to-be-observed guide that experience has shown minimizes electrical hazards to personnel and buildings and their contents.

Now, we are going to distinguish between three important electrical terms. As a CE, you will need to know the difference between the terms grounded, grounded conductor, and grounding conductor. Grounded, as defined by the NEC(c), means connected to the earth or to some other conducting body that serves in place of the earth. A grounded conductor is a circuit conductor that is intentionally grounded. A grounding conductor is a conductor used in connecting equipment in the circuit of a wiring system to a grounding electrode or electrodes. As a CE, you should make it a point to learn the difference between these terms. You will see them and hear them discussed throughout your career. Use the NEC(c), study it, and learn it. A working familiarity with this reference will prove useful to you, and, as you advance in rate, teach your junior personnel the importance of this valuable guide.

SERVICE ENTRANCE AND DISTRIBUTION PANELS The starting point for interior wiring is the service entrance. It is connected to the service drop. The service entrance is made up of several components, but before we get into the specifics concerning the service entrance, let us look briefly at the wiring system used to supply a building. The types of electrical systems that are to be installed are determined mostly by what the building is to be used for and the type of equipment that is to be used. Generally speaking, electrical loads are divided into four categories: two-wire, single-phase; three-wire, single-phase; three-wire, three-phase; and four-wire, three-phase. 

WIRING SYSTEMS The simplest wiring system is a two-wire, single-phase type, as shown in figure 5-1. This system is used

Figure 5-1.- Two-wire, single-phase system.

in small buildings where the primary requirement is lighting. It can also be used to operate 120-volt appliances and motors. The two-wire system consists of one ungrounded, insulated conductor and one identified (grounded) conductor, which is called the neutral. This system is limited to the operation of 120- volt equipment and relatively light loads of 50 amperes or less. Larger loads can be better served by another type of wiring system. The two-wire system requires the use of an equipment-grounding conductor that may be a separate conductor, conduit, or other recognized means of grounding.

Figure 5-2 shows the three-wire, single-phase wiring system, used both for lighting and power. This

system, commonly known as "220," "110," (single phase), uses two ungrounded conductors and a neutral conductor, which is grounded. It provides 110 volts between each ungrounded conductor and the neutral. It

also provides 220 volts between the two ungrounded conductors. This system is used for lighting and power loads, such as air conditioners and heating equipment. The three-wire, single-phase system provides up to twice the power that is available from a two-wire system with conductors of the same size provided that the load is balanced between the two ungrounded conductors. The 110-three-wire, 220 volts is the most common system used in residences today. This system also requires the use of an equipment-grounding conductor.

A second type of three-wire system is the three-wire, three-phase system shown in figure 5-3. This system is used to furnish power, usually 220 volts, to installed equipment. If some lighting is needed, 220- volt fixtures and bulbs can be installed, but be aware that there are certain restrictions placed on lighting circuits exceeding 120 volts. When substantial amounts of power are required, higher voltages, such as 480 volts ac, maybe provided with this type of system.

Figure 5-2.- Three-wire, single-phase system.

Figure 5-3.- Three-wire, three-phase system. The last type of wiring system in common use is the four-wire, three-phase system (fig. 5-4). This system has three ungrounded phase conductors plus a grounded neutral. This system is a combination of light and power and offers quite a cost reduction over a three-wire, single-phase system for the same amount of power. The usual voltages are 120/ 208 or 120/ 240

VAC, depending on the type of transformer connections used.