CHAPTER 4 POWER DISTRIBUTION

A power distribution system includes all parts of an electrical system between the power source and the customer's service entrance. It includes the use of overhead and underground transmission methods and the equipment required for the control and protection of the system and personal. The power source may be either a local generating plant or a high-voltage transmission line feeding a substation that reduces the high voltage to a voltage suitable for local distribution. At most advanced bases the source of power will be generators connected directly to the load.

This chapter will be mainly concerned with the overhead distribution system. Generally speaking, an overhead distribution system can usually be installed and maintained more efficiently than an underground system. Also, for equivalent conductor size, an overhead system has higher current capacity and offers greater flexibility with regard to changes. In this chapter you will learn about line work safety, pole climbing, and the tools and equipment a lineman uses. You will learn the basics in constructing and maintaining a power distribution system as well as the component parts of the system.

SAFETY IN POWER DISTRIBUTION The topic of safety that is covered in this chapter is the most important. The potential for an accident is constantly present during construction and maintenance operations but is much greater when crew members are working on power distribution systems. The presence of HIGH VOLTAGE in your work area increases your need for heightened awareness of the potential for serious injury or death that may be caused by carelessness and the necessity to take precautions to ensure the safety of all personnel.

EQUIPMENT REQUIREMENTS Cranes, earth augers, bucket trucks, and line trucks with booms that are capable of contacting HIGH-VOLTAGE lines because of their height capabilities must be operated with caution. A minimum separation of 10 feet must be maintained between the equipment and the energized power circuits at all times. The equipment must be maintained in first-class mechanical condition. 

SAFETY FIRST must be the primary goal.

PERSONNEL SAFETY To ensure the SAFETY of all personnel working on power distribution lines, you should observe the following safety precautions: Ensure that all hot-line equipment is routinely tested according to the manufacturer's specifications before use.

Ensure that all hot-line equipment, including rubber gloves, is stored in appropriate containers to provide the required physical protection. Perform air leak tests on rubber gloves before each use.

Never use rubber gloves without the leather outer protectors.

Ensure that the hard hats of crew members are rated to withstand 20,000 Vac and that no metal devices are or have been attached to them. All members of the line crew must be trained in the application of the first-aid techniques required to treat victims of electrical shock. Ensure that no individual is ever allowed to work alone or near circuits or devices conducting electrical energy over 30 Vac. Tag and lock out all circuits that are de-energized to perform work.

Install ground sets between the electrical source and your work on all de-energized circuits when the disconnecting means is not in sight or when the potential for contact between the de-energized circuit and an energized circuit is present. Maintain a minimum of 3-foot clearance between personnel and any live power circuit or device conducting between 600 and 20,000 Vac. Higher voltages require an increased separation of personnel and energized circuits.

Many other safety procedures are required on the job- too many to list here. The Lineman's and Cableman's Handbook, the Electrical Transmission and Distibution Safety Manual, NAVFAC P-1060, and Occupational Safety and Health Administration instructions are a few References you need to read to learn more about job safety.

POWER LINE COMPONENTS Power line components are the different items used to construct a power distribution line. The basic components of a power line are poles, guys, crossarms, insulators, and conductors.

POLES The three types of poles used most frequently in pole-line construction are wood, concrete, and steel. You will find all three types of poles in the field, but most of your work will be with the wooden type.

All wooden poles used for line work are chemically treated to resist damage caused by insects and rotting. Many of the older poles now in use were treated with creosote. Most new poles are treated with less toxic chemicals and are therefore safer to work with.

WARNING Creosote is a toxic compound that irritates the skin and sometimes causes blistering. You should use extra care when working around poles treated with creosote to prevent contact between these poles and the bare skin.

The supply of wood poles available for use in constructing electric power lines has decreased in recent years. Substitute materials, such as concrete, aluminum, fiber glass and laminated and composite wood poles, are now being used.

The classification of wooden poles is determined by the length, circumference at the top, and circumference measured 6 feet from the butt end. Pole sizes begin at 20 feet and are increased in 5-foot increments up to 90 feet in length. Pole-top circumference increases 2 inches for every class from Class 7 to Class 1. The Navy, however, does not normally order poles smaller than Class 5.

American National Standard, ANSI 05.1, entitled "Specifications and Dimensions for Wood Poles" provides technical data for wood utility poles.