US Army Engineer Course - Electricity V (Install Systems, Equipment, And Component Grounds) En5144

46 Pages·2021·1.06 MB·English

SUBCOURSE
EDITION

EN5144
B

US ARMY ENGINEER SCHOOL

INSTALL SYSTEM, EQUIPMENT
AND COMPONENT GROUNDS

INSTALL SYSTEM, EQUIPMENT, AND

COMPONENT GROUNDS

Subcourse Number EN 5144

EDITION B

United States Army Engineer School
Fort Leonard Wood, Missouri 65473

5 Credit Hours

Edition Date: October 1999

SUBCOURSE OVERVIEW

This subcourse is designed to teach the knowledge necessary to install grounding electrodes and circuit
grounds. The subcourse contains two lessons relating to Soldier Training Publication (STP) 5-51R12-SM-
TG, Task 051-246-1104, Install Grounding Systems Equipment and Component Grounds.

There are no prerequisites for this subcourse.

This subcourse reflects the doctrine which was current at the time it was prepared. In your own work
situation, always refer to the latest official publications.

Unless otherwise stated, the masculine gender of singular pronouns is used to refer to both men and
women.

*This publication contains copyrighted material.

Appendix A contains a metric conversion chart.

TERMINAL LEARNING OBJECTIVE

ACTION:
You will describe the procedures used to install grounding systems.

CONDITION:
You will be given the material in this subcourse, a number (No.) 2 pencil, and an
Army Correspondence Course Program (ACCP) examination response sheet.

STANDARD:
To demonstrate competency of this task, you must achieve a minimum of 70 percent
on this subcourse.

*Table 2-1, page 2-4; Table 2-2, page 2-5; and Table 2-3, page 2-8, were extracted from the National
Electrical Code (NEC), printed and distributed by the National Fire Protection Association.

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TABLE OF CONTENTS

Section
Page

Subcourse Overview.......................................................................................................................................i

Administrative Instructions..........................................................................................................................iii

Grading and Certification Instructions........................................................................................................iii

Lesson 1: Install Grounding Electrodes...................................................................................................1-1

Practice Exercise......................................................................................................................................1-13

Answer Key and Feedback......................................................................................................................1-16

Lesson 2: Install Circuit Grounds..............................................................................................................2-1

Practice Exercise..........................................................................................................................2-11

Answer Key and Feedback......................................................................................................................2-14

Appendix A - Metric Conversion Chart ..................................................................................................A-1

Appendix B - List of Common Acronyms ..............................................................................................B-1

Appendix C - Recommended Reading List..............................................................................................C-1

Student Inquiry Sheets

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THIS PAGE INTENTIONALLY LEFT BLANK

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THIS PAGE IS INTENTIONALLY LEFT BLANK.

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LESSON 1

INSTALL GROUNDING ELECTRODES

Critical Task: 051-246-1104

OVERVIEW

LESSON DESCRIPTION:

In this lesson, you will learn to describe the procedures used to install grounding electrodes.

TERMINAL LEARNING OBJECTIVE:

ACTION:
You will learn to describe the procedures used to install grounding electrodes.

CONDITION:
You will be given the material contained in this lesson. You will work at your own
pace and in your own selected environment with no supervision.

STANDARD:
You will correctly answer the practice exercise questions at the end of this lesson.

REFERENCES:
The material contained in this lesson was derived from STP 5-51R12-SM-TG and
Section 250 of the NEC.

INTRODUCTION

An electrician's most important concern is to ensure that all electrical circuits are grounded. In this
lesson, you will be shown how to properly select and place grounding electrodes. As an electrician, you
must be able to install and test electrical circuits to ensure that you have a proper ground.

1-1. Systems. Grounding systems are installed using grounding rods, conductors, or plates. Grounding
rods must be copper, steel, or iron/steel (galvanized) pipe that is at least 8 feet long. Ground resistance
must be less than 25 ohms to ground (earth). In order to get resistance below 25 ohms to ground, you
may need to drive a ground rod deeper than 8 feet, install additional rods, or add chemicals to the soil.
Metal water pipes can be used to supplement a grounding system. One of the most important parts of
electrical installation is the grounding rod (Figure 1-1, page 1-2).

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Figure 1-1. Grounding rod

a. The best grounding rod (electrode) is made of copper (nonferrous metal) and is at least 1/2

inch in diameter (Figure 1-2).

Figure 1-2. Copper grounding rod

b. A copper-coated, steel grounding rod is at least 1/2 inch in diameter (Figure 1-3).

Figure 1-3. Copper-coated, steel grounding rod

c. A solid-steel (ferrous metal) grounding rod is at least 5/8 inch in diameter (Figure 1-4).

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Figure 1-4. Solid-steel grounding rod

d. An iron/steel (galvanized) grounding rod is at least 3/4 inch in diameter (Figure 1-5).

Figure 1-5. Iron/steel (galvanized) grounding rod

e. For ease of storing, some grounding rods are constructed in 3-foot sections (Figure 1-6).

Figure 1-6. Grounding-rod sections

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1-2. Installing Grounding Rods. Grounding rods are driven into the earth to a depth of at least 8 feet
(Figure 1-7). This should reach the moisture level in most areas.

Figure 1-7. Depth of grounding rod

a. If rock is hit at less than 8 feet, the grounding rod can be driven at an angle but the angle

cannot exceed 45 degrees (Figure 1-8).

Figure 1-8. Grounding rod driven at an angle

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b. A grounding rod can also be buried on top of rock in a trench that is 2 1/2 feet deep and 8

feet long (Figures 1-9 and 1-10).

Figure 1-9. Grounding rod buried on top of rock

Figure 1-10. Cutting a trench

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c. Ground clamps (Figure 1-11) hold the ground conductor and the grounding rod together

without losing conductivity when exposed to weather and abuse. Ensure that the ground conductor is
opposite to the screw-on clamp. The upper end of the grounding rod must be flush with or below
ground level unless the connection is protected against physical damage.

Figure 1-11. Ground clamps

1-3. Resistance. The resistance between a grounding rod and the earth should be less than 25 ohms.
Check the ground resistance with a megohm meter (Figure 1-12). This check should be made with the
grounding jumper between the water pipe or a good ground and the electrical system. A metallic cold-
water system makes a good point for testing the resistance of an electrical grounding system. If 25
ohms to ground cannot be achieved, take the following actions:

Figure 1-12. Megohm meter

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a. Drive additional 8-foot grounding rods into the earth and bond them together. The rods

must be at least 6 feet apart (Figure 1-13).

Figure 1-13. Additional grounding rods

b. Drive grounding rods deeper, if necessary, to reach the water table (Figure 1-14).

Figure 1-14. Grounding rod reaching the water table

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c. Treat the soil with chemicals if the ground resistance is still over 25 ohms after using the

methods described in paragraphs 1-3a and 1-3b. Treat the soil by-

•
Digging a circular trench around the grounding electrode. The trench should be 1 foot deep
and 9 inches away from the electrode (Figure 1-15).

•
Filling the trench with 50 to 100 pounds of rock salt (copper sulfate or magnesium sulfate
may also be used) and then filling the trench with water. As the water goes through the salt
into the ground, resistance should be lowered. Natural rainfall will continue the process, but
you must replace the rock salt every two years (Figure 1-16).

Figure 1-15. Trench dug around grounding rod

Figure 1-16. Trench filled with rock salt

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1-4. Grounding Plates. Grounding plates (Figure 1-17) are sometimes required by a construction print.
They offer a better grounding system than grounding rods and are generally used in permanent
communication and computer sites. Unless prints or specifications call for larger plates, the total surface
area of grounding plates must be 2 square feet.

Figure 1-17. Grounding plate

a. Iron or steel grounding plates must be at least 1/4 inch thick (Figure 1-18)

Figure 1-18. Iron or steel grounding plate

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b. Nonferrous (copper or brass) grounding plates must be at least 1/16 inch thick (Figure 1-19).

Figure 1-19. Nonferrous grounding plate

c. The copper conductor, the clamp, and the plate are bolted together (Figure 1-20).

Figure 1-20. Conductor, clamp, and plate bolted together

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