Feeder Cable Connections While the electric generator is being installed and serviced, a part of your crew can connect it to the load. Essentially, this connection consists of running wire or cable from the generator to the load. At the load end, the cable is connected to a distribution terminal. At the generator end, the cable is connected either to the output terminals of a main circuit breaker or a load terminal board. Before the wires are run and connections are made, it will be up to you to do the following:
1. Determine the correct size of wire or cable to use.
2. Decide whether the wire or cable will be buried, carried overhead on poles, or run in conduit.
3. Check the generator lead connections of the plant to see that they are arranged for the proper voltage output.
The information contained in the following paragraphs will help you in these tasks.
CABLE SELECTION. - If the wrong size con- ductor is used in the load cable, various troubles may occur. If the conductor is too small to carry the current demanded by the load, it will heat up and possibly cause a fire or an open circuit. Even though the con- ductor is large enough to carry the load current safely, its length might result in a lumped resistance that produces an excessive voltage drop. An excessive voltage drop results in a reduced voltage at the load end. This voltage drop should not exceed 3 percent for power loads, 3 percent for lighting loads, or 6 percent for combined power and lighting loads.
Select a feeder conductor capable of carrying 150 per cent of rated generator amperes to eliminate over- loading and voltage drop problems. Refer to the National Electrical Code® tables for conductor ampacities. These tables are 310-16, 310-17, 310-18, and 310-19. You also should refer to the notes to ampacity tables following table 310-19.
CABLE INSTALLATION. - The load cable may be installed overhead or underground. In an emergency installation, time is the important factor. It may be necessary to use trees. pilings, 4 by 4s, or other temporary line supports to complete the installation. Such measures are temporary; eventually, you will have to erect poles and string the wire or bury it underground. If the installation is near an airfield, it may be necessary to place the wires underground at the 3-6 beginning. Wire placed underground should be direct- burial. rubber-jacketed cable: otherwise, it will not last long.
Direct burying of cable for permanent installation calls for a few simple precautions to ensure uninterrupted service. They are as follows:
1. Dig the trench deep enough so that the cable can be buried at least 18 inches (24 inches in traffic areas and under roadways) below the surface of the ground to prevent disturbance of the cable by frost or subsequent surface digging.
2. After laying the cable and before backfilling, cover it with soil free from stones, rocks. and so forth. That will prevent the cable from being damaged in the event the surrounding soil is disturbed by flooding or frost heaving.
When you are in charge of a generating station, you will be responsible for scheduling around-the- clock watches to ensure a continuous and adequate amount of electrical power. Depending on the number of operating personnel available, the watches are evenly divided over the 24-hour period. A common practice is to schedule 6-hour watches, or they may be stretched to 8-hour watches without working undue hardship on the part of the crew members. Watches exceeding 8 hours, however, should be avoided unless emergency conditions dictate their use.
The duties assigned to the personnel on generator watches can be grouped into three main categories: (1) operating the equipment, (2) maintaining the equipment, and (3) keeping the daily operating log. Operating and maintaining the generating equipment will be covered in the succeeding sections of this chapter, so for the present you can concentrate on the importance of the third duty of the station operator - keeping a daily operating log.
The number of operating hours are recorded in the generating station log. The log serves as a basis for determining when a particular piece of electrical equipment is ready for inspection and maintenance. The station log can be used in conjunction with previous logs to spot gradual changes in equipment condition that ordinarily are difficult to detect in day- to-day operation. It is particularly important that you impress upon your watch standers the necessity for taking accurate readings at periods specified by local operating conditions.Continue Reading