US Army Engineer Course - Electricity II (Install Service Entrance Systems) EN5141

33 Pages·2021·0.98 MB·English

SUBCOURSE
EDITION

EN5141
B

US ARMY ENGINEER SCHOOL

INSTALL SERVICE-
ENTRANCE SYSTEMS

INSTALL SERVICE-

ENTRANCE SYSTEMS

Subcourse Number EN5141

EDITION B

United States Army Engineer School
Fort Leonard Wood, Missouri 65473

4 Credit Hours

Edition Date: June 1999

SUBCOURSE OVERVIEW

This subcourse is part of Soldier Training Publication (STP) 5-51R12-SM-TG, Install Service Entrance
Systems. It is designed to teach the knowledge and skills necessary to perform tasks related to installing
service-entrance (SE) systems. The subcourse is presented in two lessons, each corresponding to a
terminal learning objective as indicated below.

There are no prerequisites for this subcourse.

This subcourse reflects the doctrine which was current at the time the subcourse 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.

TERMINAL LEARNING OBJECTIVE

ACTION:
You will learn the procedures used to install SE systems.

CONDITION:
You will be given the material in this subcourse 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.

i
EN5141

TABLE OF CONTENTS

Section
Page

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

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

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

Lesson 1: Overhead Entrance Systems ..................................................................................................1-1

Practice Exercise.......................................................................................................................1-20

Answer Key and Feedback.......................................................................................................1-22

Lesson 2: Underground Service .............................................................................................................2-1

Practice Exercise.........................................................................................................................2-6

Answer Key and Feedback ........................................................................................................2-8

Examination..........................................................................................................................................E -1

Appendix A: List of Common Acronyms ...........................................................................................A-1

Appendix B: Recommended Reading List ............................................................................................B-1

Student Inquiry Sheets

ii
EN5141

LESSON 1

OVERHEAD ENTRANCE SYSTEMS

Critical Task: 051-246-1102

OVERVIEW

LESSON DESCRIPTION:

In this lesson you will learn to describe an overhead entrance system.

TERMINAL LEARNING OBJECTIVE:

ACTION:
You will learn the procedures used to install an overhead entrance system.

CONDITION:
You will be given subcourse booklet EN5141 and an ACCP examination response
sheet. You will work at your own pace and in your own selected environment
with no supervision.

STANDARDS:
You will correctly answer 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
FM 5-424.

INTRODUCTION

Overhead entrance systems are the conductors and the equipment used for the control and protection of
electrical circuits, equipment, and personnel. The SE is the end of the interior electrical system. This
lesson will teach you how to describe an overhead entrance system.

The conductors from the power pole to the building are called service drops as shown in Figure 1-1,
page 1-2. The minimum height of a service drop above the ground and on the building is determined
by its location.

1-1
EN5141

Figure 1-1. Clearances for a service drop

Above foot-traffic areas, 10 feet of vertical clearance is necessary for service drops supported and
wrapped on a ground messenger having 150 volts to ground between the current-carrying conductors
(Figure 1-2). Remember, the 10-foot minimum clearance is measured from the lowest point of the SE
cable.

Figure 1-2. Service drop above a foot-traffic area

1-2
EN5141

Above residential property, driveways, and areas not subject to truck traffic, 12 feet of vertical clearance
is maintained for conductors having 300 volts to ground (Figure 1-3).

Figure 1-3. Service drop above residential property

not subject to truck traffic (300 volts to ground)

Above residential property, driveways, and commercial property not subject to truck traffic, 15 feet of
vertical clearance is maintained for conductors having 600 volts to ground (Figure 1-4). Automobiles
and small vehicles can clear an SE cable with a minimum clearance of 15 feet to ground.

Figure 1-4. Service drop above residential property

not subject to truck traffic (600 volts to ground)

1-3
EN5141

Above public streets and parking areas subject to truck traffic, 18 feet of vertical clearance is required in
Figure 1-5. A 20-foot-high load did not clear the service drop.

Figure 1-5. A high load damaging a service drop

Above a peaked roof, having a 1:3 pitch or more, an 18-inch vertical clearance is necessary when the
voltage between conductors is less than 300 volts and the SE is a mast within 48 inches of the roofs
edge (Figure 1-6).

Figure 1-6. Clearance between the roof and

the service drop (300 volts)

1-4
EN5141

Conductors that carry more than 300 volts require an 8-foot vertical clearance (Figure 1-7).

Figure 1-7. Clearance between the roof and the

service drop (300 volts)

Conductors that are installed at the side of a window or below it must have a 3-foot clearance (Figure 1-
8).

Figure 1-8. Conductor clearance from windows

1-5
EN5141

For fire escapes, porches, or platforms, conductors must have 3 feet of horizontal clearance from the
object and 10 feet of vertical clearance from the ground (Figures 1-9 and 1-10).

Figure 1-9. Fire escape/platform clearance

Figure 1-10. Clearance above ground level

1-6
EN5141

SE Requirements: Attachment of Service Drops

Use back supports in walls that are not strong enough to support a service drop in adverse conditions
(wind, snow, or ice) (Figure 1-11). A 2-inch by 4-foot back support gives added strength to the wall.

Figure 1-11. Back support installed in wall

A single-cable system supports hot conductors and is hooked to the feed-through dead end (Figure 1-12).
The cable that supports the service-drop conductors is clamped by the feed-through clamp and coupled
to the ground conductors. The cable support is part of the ground system.

Figure 1-12. Grounded messenger cable providing support

1-7
EN5141

The bare neutral conductor is used as the messenger cable (Figure 1-13). By wrapping the hot
conductors around the messenger cable, all the weight of the service drop is on the uninsulated
neutral/messenger cable.

Figure 1-13. Hot conductors wrapped around a neutral/messenger cable.

In a typical service-drop cable, the neutral conductor is used to attach the cable to the dead end (Figure
1-14). The feed-through clamp is built so that the pull of the conductors makes the clamp tighter on the
neutral/messenger cable.

Figure 1-14. Feed-through clamp

attached to the service spool

1-8
EN5141

Service drops are also dead-ended to a building by using secondary racks (Figure 1-15). When heavy
service drops are installed on buildings, use secondary racks.

Figure 1-15. Service drop attached to a secondary rack

When individual conductors are installed, many of the installations are dead-ended by using service
spools made of porcelain (Figure 1-16). One service spool is screwed or bolted to the wall.

Figure 1-16. Service drop attached to service spools

1-9
EN5141

Service masts can dead-end individual conductors and an insulator bracket is used for this purpose
(Figure 1-17). An insulator bracket can also be used when service conductors are wrapped around a
messenger cable but feed-through clamp will be required.

Figure 1-17. Use of insulator brackets

1-10
EN5141

Most service masts use a single, dead-end bracket and a service cable (Figure 1-18). This makes a neat
installation. Although time-consuming to install, a service mast is the best method for service
installation.

Figure 1-18. Insulator bracket with feed-through clamp

SE Requirements: Installation Procedures

SE cable (Figure 1-19) has a flame-retardant, moisture-resistant covering. The neutral conductor (copper
or aluminum) is twisted into a pigtail so that it can be clamped into the grounding system.

Figure 1-19. SE cable

1-11
EN5141

SE cable must be supported within 12 inches of the service head and all boxes, and then supported every
4 1/2 feet thereafter. When a service head is unavailable an expedient service head can be made. The
SE cable is bent into a gooseneck and secured with tape (Figure 1-20). Service heads are located above
the service drop to prevent water from entering the cable run.

Figure 1-20. Expedient head

When installed as a service mast, an SE using rigid conduit provides protection for the conductors and a
strong contact point for the service drop. A service-mast system is used when greater overhead roof
clearance is needed (Figure 1-21).

Figure 1-21. Service mast using rigid conduct

1-12
EN5141