UNITED STATES DEPARTMENT OF AGRICULTURE

Rural Utilities Service

**BULLETIN 1751F-805**

**SUBJECT: [Electrical Protection at Customer Locations]{.underline}**

**TO:** All Telecommunications Borrowers

RUS Telecommunications Staff

**EFFECTIVE** **DATE:** Date of Approval

**EXPIRATION DATE:** Seven years from effective date.

**OFFICE OF PRIMARY INTEREST:** Engineering Standards Branch,
Telecommunications Standards Division

**PREVIOUS INSTRUCTIONS:** This bulletin replaces Telecommunications
Engineering and Construction Manual (TE&CM) Section 805, Number 8,
issued August 1980.

**FILING INSTRUCTIONS:** Discard TE&CM 805 and replace it with this
Bulletin. File this bulletin with 7 CFR 1751 and REANET.

**PURPOSE:** To provide technical information for use in the design,
construction and operation of RUS Borrowers\' telecommunications
systems. This bulletin includes an outline of protection principles that
should be employed on telecommunications circuits at customer service
access locations, including the application and installation of
subscriber primary protectors and applicable grounding techniques.
Supplemental information with respect to installations at customer
locations is included in RUS Bulletins 345-52 and 345─154.

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
\_\_\_\_\_\_\_\_\_\_\_\_

Administrator Date

**TABLE OF CONTENTS**

.Begin Table C.

1\. GENERAL 6

1.1 Scope 6

1.2 Primary Protector Use 6

2\. PROTECTION PRINCIPLES 6

2.1 Problem Sources 6

2.2 Protection Objectives 7

2.3 Protection Methods 7

2.4 Additional Information 8

3\. TELECOMMUNICATIONS PRIMARY PROTECTOR TYPES 8

3.1 Preferred Protectors 8

3.2 Fuseless Primary Protectors 8

3.3 Fused Type 9

3.4 Solid─State Arresters 10

4\. PRIMARY PROTECTOR INSTALLATIONS 10

4.1 Protector Locations 10

4.2 Primary Protector Selection 10

4.3 \"Listed\" Drop Wire 10

4.4 Telecommunications Service Drop Designs 11

5\. GROUNDING AND BONDING - PERMANENT INSTALLATIONS 11

5.1 Copper Grounding and Bonding Materials 11

5.2 Bonding Power and Telecommunications Systems 11

5.3 Grounding Primary Protectors at Premises 12

5.4 Grounding Electrode Choices 12

5.5 Recommended Primary Protector Installations 12

5.6 Ground Rod(s) Without Bonds 14

5.7 Grounding Conductors and Connections 14

5.8 Where Separate Ground Rods are Used 14

5.9 Protectors Not Near Electric Service Ground 15

5.10 Section 250 of the NEC 15

5.11 Multipair Fuseless Primary Protectors 16

6\. GROUNDING AND BONDING - MOBILE HOMES AND TRAILERS 16

6.1 Protection of Mobile Homes 16

6.2 Primary Protectors 17

6.3 Preferred Primary Protector Installation 17

6.4 Another Installation Method 17

7\. AC POWER SERVICE PROTECTION 18

7.1 Equipment Damage 18

7.2 Protection of AC Power Service 18

7.3 Protector Coordination 19

7.4 Power Company Practices 20

.End Table C.

FIGURES

.Begin Table F.

Figure 1 Example Without Common Grounding 21

Figure 2 Example With Common Grounding 22

Figure 3 Mobile Home with Bond to Power 23

Figure 4 Mobile Home Without Bond to Power 24

Figure 5 Typical Power Service Protector Installation 25

.End Table F.

TABLE

.Begin Table T.

Table 1 Grounding Wire Gauge for Fuseless Protectors 16

.End Table T.

INDEX:

Protection

Protection, Electrical

Protection, Subscriber Stations

Subscriber Stations

**ABBREVIATIONS**

A Unit of electrical current, amperes

ac Alternating current

AHJ Authority Having Jurisdiction

AWG American Wire Gauge

ANSI American National Standards Institute

CATV Community Antenna Television

CPE Customer Premises Equipment (customer owned)

cm Unit of length, centimeter (1/100 of a meter)

FCC Federal Communications Commission

Hz Unit of Frequency, hertz (cycles per second)

km Unit of length, kilometer (1000 meters)

m Unit of length, meter (equivalent to 3.28 feet)

mm Unit of length, millimeter (1/1000 of a meter)

MGN Multigrounded Neutral

NEC National Electrical Code

NESC National Electrical Safety Code

NFPA National Fire Protection Association

PABX Private Automatic Branch Exchange

TE&CM Telecommunications Engineering and Construction Manual

Ω Greek letter Omega, symbol for resistance unit, ohms

**DEFINITIONS**

**Authority Having Jurisdiction:** The state, county, or local agency
that regulates the requirements to be observed for installing electrical
wiring and equipment in, on, or near premises and buildings. (Note: By
RUS loan contract and mortgage provisions, RUS requires borrowers to
observe the National Electrical Code provisions when using RUS loan
funds and, thus, in areas where there is no local Authority Having
Jurisdiction, RUS is effectively the Authority Having Jurisdiction.)

**Common grounding:** The intentional interconnection of all separate
grounding systems and grounded facilities existing at a premises. This
includes such entities as the power system ground, metallic water
systems, telecommunications primary protector grounds, community antenna
television grounds, etc.

**Fuse Link:** A length of finer gauge wire in series with a coarser
gauge wire, for the purpose of \"fusing\" open during an abnormally high
current condition. A fuse link normally provides protection from
currents which could otherwise heat conductors and start fires.

**Listed:** Equipment or materials included in a list published by an
organization which is acceptable to the Authority Having
Jurisdiction (AHJ). The organization has to be concerned with product
evaluation and maintain periodic inspection of the manufacturers\'
production of listed equipment or materials. The listing has to state
either that the equipment or material meets appropriate designated
standards or has been tested and found suitable for use in a specified
manner. (This includes organizations such as Underwriters Laboratories,
ETL Testing Laboratories, etc., but [not]{.underline} RUS and RUS\' List
of Materials.)

**Multigrounded Neutral:** A power system neutral conductor which is
connected to purposefully installed (made) electrodes or existing
electrodes at least four times per mile (1.6 km) in addition to the
grounding connections at individual services and each transformer
location.

.c.**1. GENERAL**;

.c.:**1.1** **[Scope]{.underline}**;: This bulletin considers
telecommunications subscriber primary protector installations at private
residences, small businesses, and mobile homes. The information
presented is general in nature and is intended to apply to the typical
installations that most RUS borrowers will encounter. Details on other
specific protection installations may be found in the 800 series of the
Telecommunications Engineering and Construction Manuals (TE&CM)
(proposed conversion to REA Bulletins 1751F-801 through 1751F─825). It
should be noted that protection of telecommunications customer premises
equipment at power generating stations and power substations involves
special concerns. Because of their special considerations, RUS
recommends that borrowers consider retaining the services of a
consulting engineer that specializes in such protection designs.

.c.:**1.2** **[Primary Protector Use]{.underline}**;: To limit hazards
resulting from power circuit and lightning surges, rural area telephone
companies install suitable primary protectors at virtually all customer
access locations. This practice applies whether the customer is served
by aerial, buried or underground plant. All primary protector
installations have to comply with applicable requirements of the
National Electrical Code[^1] (NEC) \[formally identified as
ANSI/NFPA 70\] and any applicable local codes which are more stringent.
The NEC requires that primary protectors be installed on all
telecommunications circuits unless the circuits are served entirely
within a city \"block\" and the circuits serving the customer are not
exposed to possible contact with power circuits operating at 300 volts
or higher. Because RUS borrowers rarely encounter such (unexposed)
circuits, RUS expects all customer circuits to be protected.

.c.**2. PROTECTION PRINCIPLES**;

**.c.:2.1 [Problem Sources]{.underline}**;: Subscriber circuits and the
customer equipment connected to them may be subjected to abnormal
voltage and current transients caused by: (1) lightning surges,
(2) contacts between telecommunications outside plant conductors and
power distribution conductors, (3) induction from the magnetic fields
associated with power circuits or lightning, and (4) conduction of power
fault or lightning currents in the earth or other electrical conductors
nearby the telecommunications plant. A detailed discussion of these
sources is provided in RUS Bulletin 1751F─801.

.c.:**2.2 [Protection Objectives]{.underline}**;: Telecommunications
protection measures are necessary to help prevent: (1) electric shock to
telecommunications users and the general public that may come into
contact with plant facilities, (2) damage to the subscribers\' premises
or equipment; and (3) damage to telephone company equipment.

**2.2.1** **[Customer Equipment Attachments]{.underline}**: Rulings by
the Federal Communications Commission (FCC) have made it acceptable for
subscribers to attach their own equipment directly to the switched
network where it may be exposed to the transients discussed in 2.1.
Today\'s customers are taking advantage of this freedom and are
connecting several telephones to their lines. In addition, customers are
also connecting sophisticated electronic devices such as facsimile
machines, telephone answering devices, burglar and fire alarms,
computers (via modems) and many other types of devices. To help avoid
possible equipment operational upset or damage, RUS recommends that
primary protectors be installed on all telecommunications circuits
financed with RUS loan funds.

.c.:**2.3 [Protection Methods]{.underline}**;: The basic principles
which help to prevent harmful potentials at telecommunications
subscribers\' locations are twofold: (1) common grounding (bonding) of
all metallic utilities at the premises, and (2) use of appropriate
primary protectors on telecommunications conductors to divert lightning
and abnormal power currents to earth.

**2.3.1 [Common Grounding (Bonding) of Utilities]{.underline}**:
Utilities requiring common grounding are: (1) the telecommunications
system, (2) the power system, (3) metallic water pipe systems and (4)
Community Antenna Television (CATV). Metallic hardware associated with
all of these systems may be handled by customers and the development of
excessive voltages between them, which could present a serious shock
hazard, can be minimized by common grounding (bonding). The grounding
electrodes of all these systems have to be bonded together at all
installations. Bonding has to be done whether or not the water system is
considered to be a low resistance ground or not.

**2.3.2 [Bonding Purpose]{.underline}**: The purpose for bonding
separate grounding electrodes is depicted graphically in Figures 1 and
2.

**2.3.2.1 [Without Bonding]{.underline}**: Figure 1 illustrates how the
voltage difference between two electrodes rises to hazardous levels when
a lightning surge on the power grounding system flows to earth via the
power grounding electrode. In the example, a 500 A surge flows through
the 25 Ω power electrode resistance and causes 12,500 volts to appear
across the power grounding electrode. Since the telecommunications
electrode is remotely located (and for illustration purposes here not
affected by the rise in potential at the power grounding electrode) the
12,500 volts appears between the two system electrodes. If the current
surge entered via the telecommunications grounding system, results would
be about the same with (500 A x 37.5 Ω) or 18,750 volts appearing across
the telecommunications grounding electrode and between the two system
grounding electrodes.

**2.3.2.2 [With Bonding]{.underline}**: Figure 2 illustrates how the
voltage differences between the two electrodes are minimized when the
electrodes are bonded to one another as required by the NEC. (In the
example a 100 foot (30.5 m) length of #6 AWG copper conductor is assumed
to bond the two electrodes together). Figure 2 shows that the surge
current divides between the two bonded electrodes. In our example, a
500 A surge arriving on the power system splits with about 300 A flowing
to earth via the power grounding electrode and 200 A flowing to earth
via the bonding conductor and the telecommunications grounding
electrode. The voltage drop between the two electrodes calculates to be
(200 A x 0.04 Ω) or 8 volts. If the 500 A surge entered via the
telecommunications system, results would be similar with (300 A x
0.04 Ω) or 12 volts appearing between the two electrodes. In both
situations the voltage difference is drastically reduced from values
expected without bonding of the two electrodes. Shorter bonding
conductors or use of the power grounding system for grounding primary
protectors will help to reduce voltage differences between utilities
even more.

.c.:**2.4** **[Additional Information]{.underline}**;: Supplementary
information on grounding is covered in RUS Bulletin 1751F-802.

.c.**3. TELECOMMUNICATIONS PRIMARY PROTECTOR TYPES**;

.c.:**3.1 [Preferred Protectors]{.underline}**;: There are two types of
primary protectors: fused type and fuseless type. Fuseless type
protectors are preferred because they provide more effective protection
than fused types and because the maintenance associated with these units
is normally lower than that for fused type protectors. Fused type
primary protectors should be avoided except where the requirements for
fuseless primary protectors cannot be met. The following paragraphs
describe the two types of protector in more detail.

.c.:**3.2 [Fuseless Primary Protectors]{.underline}**;

**3.2.1** **[Design]{.underline}:** A fuseless primary protector employs
white coded (350 to 600 Volts) carbon air-gap, orange coded gas tubes,
or equivalent surge arresters connected between each line conductor and
ground. These arresters have a breakdown value adequate for the
protection of personnel and well below the dielectric strength of
equipment and wiring furnished by a telephone company. Manufacturers
produce fuseless primary protectors with various current─carrying
capacities which \"Listing\" agencies recognize by noting the maximum
fuse link with which fuseless primary protectors can be used. Common
maximum fuse link ratings for fuseless primary protectors include 22,
24, and 26 AWG copper conductors with thermoplastic insulation and
20 AWG, 40 percent, copper─clad steel wire (bridle wire). Telephone
companies have to be certain to coordinate the fuse link rating for a
particular fuseless primary protector with the installation circuitry.
This means making certain that the protector used has a current─carrying
capacity appropriate for the wire or cable pair and/or the fuse link to
which the fuseless protector will be connected. On RUS financed
projects, the maximum fuse link should be 24 AWG because RUS requires
all service drops to have 22 AWG conductors.

**3.2.1.1** **[Advantages]{.underline}**: Fuseless primary protectors
are advantageous because, unlike fused primary protectors, their
grounding connection is maintained during a telecommunications line
contact with a power line. The uninterrupted grounding helps in
de─energizing a power circuit by offering additional paths to ground
which promotes higher magnitude power line fault current to facilitate
sensing and speedier operation of power line fuses and circuit breakers.
Elimination of fuses also prevents the excessive potential on drop wire
and protector terminals as would be the case with a fused type primary
protector after fuse operation resulting from a power contact. Use of
fuseless primary protectors results in a reduction in customer
maintenance visits for fuse replacement.

**3.2.1.2** **[Disadvantages]{.underline}**: Fuseless primary protectors
can not be used at every installation site and their use requires
judgements on the part of the installer with respect to the maximum fuse
wire with which the protector can be used. Fuseless primary protectors
can only be installed when the installation will be compliant with NEC
Sections 800─30(a)(1)a through 800─30(a)(1)e. Otherwise a fused primary
protector has to be used. As noted in 3.1.1, fuseless primary protectors
require coordination with the installation circuitry\'s current─carrying
capacity and the maximum fuse link design of the protector.

.c.:**3.3 [Fused Type]{.underline}**;

**3.3.1** **[Fused Primary Protectors]{.underline}**: Fused type primary
protectors employ white coded (350 to 600 Volts) air-gap, orange coded
gas tube, or equivalent surge arresters for the limitation of excessive
potentials, and fuses to limit sustained currents to a value less than
which the protector can safely carry. (Fuses in fused type primary
protectors are rated for 7 amps and the wiring inside a fused primary
protector is rated for 15 amperes per conductor continuously). The fuses
are required to open the circuit on currents resulting from power
contacts which would otherwise result in a fire hazard because of
protector overheating. One fuse is connected in each side of the line on
the line side of the arrester.

**3.3.1.1** **[Advantages]{.underline}**: Fused primary protectors
provide effective safety from fire hazards related to power contact
problems for installations where fuseless primary protectors are not
allowed by the NEC.

**3.3.1.2** **[Disadvantages]{.underline}**: With fused type primary
protectors, the grounding connection for the drop wire is lost when the
fuses operate and the drop wire and protector line terminals may remain
energized at an excessive potential. Because the line terminals of a
fused─type primary protector may remain energized after the fuses have
operated, craftspersons should exercise caution in touching terminals
until it has been verified that the terminals are safe.

.c.:**3.4 [Solid─State Arresters]{.underline}**;

**3.4.1** **[Solid─State Primary Protectors]{.underline}**: At the
present time, because of their lower peak current─carrying capability,
RUS does not recommend the use of solid─state arresters in primary
protectors used at customer premises.

.c.**4. PRIMARY PROTECTOR INSTALLATIONS;**

.c.:**4.1** **[Protector Locations]{.underline}**;: When planning and
staking customer installations the selection of primary protector
locations should be made with major emphasis on achieving common
grounding of the telephone company\'s primary protector ground with the
power system ground. The NEC requires primary protectors to be located
as close as practical to the point at which exposed telecommunications
conductors enter or attach to the building. The NEC also requires that
the metallic shield of a telecommunications cable be grounded (or
insulated) as close as practicable to the point where the cable enters
the building. RUS recommends that wherever possible grounding of a cable
shield and a primary protector be accomplished at the same location and
that the power service grounding established at the
[building]{.underline} served be used as the telecommunications primary
protector grounding electrode. See REA Bulletin 345─52, \"REA Standard
for Service Entrance and Station Protector Installations\". (Proposed
codification to 7 CFR 1755.500 through 7 CFR 1755.510)

.c.:**4.2** **[Primary Protector Selection]{.underline}**;: Protector
types and indoor versus outdoor mountings are covered in REA Bulletin
345─52. In addition to utility needs, primary protectors should be
\"Listed\" by Underwriters Laboratories, ETL Testing Laboratories, or
other similar organization acceptable to the Authority Having
Jurisdiction (AHJ). Primary protectors should also be RUS accepted or
technically accepted.

.c.:**4**.**3** **[\"Listed\" Drop Wire]{.underline}**;: The NEC
requires communications wires and cables without a metallic shield
(usually aerial drop wire and cable) between the last outdoor support
and the primary protector to be \"Listed.\"

.c.:**4.4 [Telecommunications Service Drop Designs]{.underline}**;

**4.4.1 [Shieldless Drops]{.underline}**: When shieldless cable or drop
wire is used between the last outdoor support and a fuseless primary
protector, the NEC relies on conductor fusing coordination to help
prevent fire hazards caused by a possible power conductor contact to
telecommunications plant. The NEC requires the primary protector
grounding conductor and drop wire conductor to be sized and the primary
protector to be sized (see Paragraph 3.1.1) such that none of these
circuit elements fuse open before conductors ahead of them (towards the
central office). These sacrificial conductors have to be located between
the possible point of power conductor exposure and the service drop and
may be in the form of a cable stub or a supplementary fusible link
between the wire or cable plant and the customer drop, or they may be
the outside plant wire or cable conductors themselves.

**4.4.2** **[Shielded Drops]{.underline}**: When shielded cable is used
between the last outdoor support and a fuseless primary protector, the
NEC relies on the effectively grounded metal shield to help prevent fire
hazards caused by a possible power conductor contact to
telecommunications plant. The grounded cable shield helps to draw power
line current of sufficient magnitude to cause power line fuses, circuit
breakers, etc., to quickly open the power circuit and remove the hazard.
Additionally, the NEC requires the sizing of the conductors within
shielded telecommunications drop cable to be purposefully chosen
(coordinated) such that conductors within the drop cable safely fuse
open before the protector grounding conductor or conductors within the
protector (see Paragraph 3.1.1).

.c.**5. GROUNDING AND BONDING - PERMANENT INSTALLATIONS;**

.c.:**5.1** **[Copper Grounding and Bonding Materials]{.underline}**;:
Copper is the most commonly used material for bonding and grounding
conductors and its exclusive use has been assumed throughout this
bulletin. Article 800-40(a)(2) of the NEC states: \"\...the grounding
conductor shall be copper or other corrosion─resistant conductive
material, stranded or solid.\"

.c.:**5.2** **[Bonding Power and Telecommunications
Systems]{.underline}**;: As indicated in Paragraph 2.3, it is essential
that power and telecommunications grounding systems at a subscriber\'s
access location be connected (bonded) to each other and to any metallic
water piping system in order to avoid dangerous voltage differences
within the subscriber\'s premises. Common grounding (bonding) is
essential whether or not such piping systems meet the minimum
requirements as preferred grounding electrodes or whether the
telecommunications facilities are buried. A low resistance ground is
desirable in that it aids in assuring de─energization of the power
system in the event of a contact. A low resistance ground is also
beneficial in minimizing the development of excessive potential
differences between systems, but low resistance grounds are not a
substitute for potential equalization by common grounding.

.c.:**5.3** **[Grounding Primary Protectors at Premises]{.underline}**;:
Part D of Article 800 of the NEC provides detailed information on the
proper method for grounding primary protectors and cable shields at
customer premises.

.c.:**5.4** **[Grounding Electrode Choices]{.underline}**;

**5.4.1 [NEC Provisions]{.underline}**: In Part D of Article 800, the
NEC has established three selection groupings or orders of preference
for the choice of a grounding electrode for a primary protector. These
preferences are contained in Section 800─40(b)(1), 800─40(b)(2) and
800─40(b)(3). In the first selection grouping, Section 800─40(b)(1), the
NEC requires that the primary protector grounding conductor be connected
to the nearest of any of some seven (7) cited \"acceptable\" electrodes.
It is important to note that the numbering within this selection
grouping is not an order of selection but simply a means to separate and
conveniently list choices. The intent of the NEC is that the primary
protector grounding conductor be connected to the \"acceptable\"
electrode which is nearest to where the primary protector is installed.

**5.4.2 [NEC Grounding Selection Order]{.underline}**: If none of the
electrodes cited in Section 800─40(b)(1) are available at the premises,
the installer defers then to Section 800─40(b)(2) and then to
Section 800─40(b)(3) should there be no electrodes of the type cited in
Section 800─40(b)(2).

.c.:**5.5 [Recommended Primary Protector Installations]{.underline}**;

**5.5.1 [General]{.underline}**: Primary protectors and cable drop
shields should always be installed as near as is practicable to the
selected grounding electrode with the desired installation involving as
short and as straight a primary protector grounding conductor as
possible. The location should also be coincidentally designed to be as
close to where the conductors will enter the building. As can be seen
from Paragraph 5.4, the choices of electrode can be confusing because of
their numbers and the specifics involved to assure NEC compliance. To
reduce the confusion some, the following presents the RUS recommended
order of preference for installing primary protectors:

**5.5.1.1 [Power Service Grounding System (Preferred)]{.underline}**:
Install primary protectors as close as practicable to where the
telecommunications wire or cable is to enter the building served
choosing a point which is coincidentally planned to be as close as
practicable to where some accessible part of the premises\' power
service grounding system exists. The desired installation will involve
as short and as straight a primary protector grounding conductor as
possible attached directly to the [nearest]{.underline}
[accessible]{.underline} point on the premises power service grounding
system. The power service grounding system includes any of the
following: (1) the power service accessible means external to enclosures
as covered in NEC Section 250─71(b), (2) the metallic power service
raceway, (3) the power service equipment enclosure, (4) the power
service grounding electrode conductor or grounding electrode conductor
metal enclosure, or (5) the grounding conductor or the grounding
electrode of a building or structure power disconnecting means, that is
grounded to an electrode as covered in NEC Section 250─24. Telephone
companies can ask customers to have an electrician provide the means for
bonding as prescribed in NEC Section 250─71(b) when there is no other
accessible portion of the power service grounding system available at
the premises;

**5.5.1.2 [Premises Grounding Electrode System]{.underline}**: If there
are no electric power facilities at the premises, install primary
protectors as close as practicable to an accessible point on the
building or structure grounding electrode system as covered in NEC
Section 250─81. This grounding electrode choice introduces some
confusion because NEC Section 250-81 requires that if two or more of the
four possible electrode sources cited are present at the premises that
they be bonded together. Included are (1) any metal underground water
piping in direct contact with the earth for 10 feet (3.05 meters) or
more, (2) the metal frame of a building if the frame is effectively
grounded, (3) concrete─encased electrodes meeting the provisions of NEC
Section 250─81(c), and (4) a ground ring of the type cited in
Section 250─81(d). Some of these electrodes may be quite simple to find
while others may not be so easy to spot. However, all will have to be
bonded together to form a grounding system before they can be used as
the protection grounding electrode;

**5.5.1.3 [Grounded Interior Metal Water Piping System]{.underline}**:
If there are no electric power facilities at the premises and no
premises grounding system as described in Paragraph 5.5.1.2, install
primary protectors as close as practicable to a grounded metal
underground water pipe which is in direct contact with the earth for
10 feet (3.05 meters) or more as discussed in NEC Section 250─80(a).
Please note that there are two provisos with respect to this electrode
choice: (1) The buried piping cannot be relied upon alone as the NEC
requires water piping to be attached to another, supplemental,
acceptable grounding electrode, and (2) attachment to the water piping
has to be made within 5 feet (1.52 m) of where the pipe enters the
building. (RUS recommends installing a supplemental ground rod as a
standard practice to dispel any doubt about the existence of required
supplemental grounding. The concern for attaching to the water pipe
within 5 feet (1.52 m) of the pipe\'s entry into the building is with
future piping repairs using non─metallic piping and the resultant loss
of electrical continuity);

**5.5.1.4 [Individual Electrodes]{.underline}**: If there are no
grounding electrodes of the types discussed in Paragraphs 5.5.1.1
through 5.5.1.3, install primary protectors as close as practicable to
any of the individual electrodes cited in Paragraph 5.5.1.2; or

**5.5.1.5 [Ground Rods or Pipe Electrodes]{.underline}**: If there are
no grounding electrodes of the types discussed in Paragraphs 5.5.1.1
through 5.5.1.4, install primary protectors to: (1) an effectively
grounded metal structure, or (2) a ground rod or pipe not less than
5 feet (1.52 m) in length and 1/2 inch (12.7 mm) in diameter, driven,
where practicable, into permanently damp earth and separated from
lightning conductors as covered in NEC Section 800─13 and at least
6 feet (1.83 m) from electrodes of other systems. Telephone companies
should always make ground rods their absolute [last]{.underline} choice
at a building where power is also installed. In addition, in areas of
the country where the frost line exceeds 18 inches (46 cm) use of longer
8 foot (2.4 m) rods should be used in lieu of 5 foot (1.52 m) ground
rods.

.c.:**5.6 [Ground Rod(s) Without Bonds]{.underline}**;: Use of a ground
rod as the only primary protector grounding electrode is acceptable
[only]{.underline} when the customer premises location has
[no]{.underline} internal metallic water pipe [and]{.underline} no
electric service. In all other cases, it is essential that all of the
grounding electrodes be interconnected whether or not any or all of
these are \"low resistance\" grounds. As noted in Paragraph 2.3.2,
bonding is necessary to avoid the development of hazardous voltages
between grounded systems during surge events. These voltages constitute
a possible shock hazard to telecommunications users.

**.c.:5.7** **[Grounding Conductors and Connections]{.underline}**;:
Grounding conductors from primary protectors to the various grounding
electrodes listed in Paragraphs 5.4 and 5.5 should be sized as shown in
Table 1, using insulated copper wire \"Listed\" by Underwriters
Laboratories, ETL Testing Laboratories, or some other similar
organization acceptable to the AHJ. Grounding attachments (grounding
connectors) used to connect primary protector grounding conductors to
NEC acceptable grounding electrodes should also be \"Listed\" by
Underwriters Laboratories, ETL Testing Laboratories, or some other
similar organization acceptable to the AHJ.

.c.:**5.8** **[Where Separate Ground Rods are Used]{.underline}**;:
Whenever separate ground rods are used for electric and
telecommunications facilities at a premises, the telecommunications
ground rod should be bonded with at least a #6 AWG copper wire to some
easy access point on the power grounding system, i.e., power grounding
conductor, grounding electrode, metallic conduit covering the power
grounding conductor, etc.,(see Paragraph 5.5.1.1). If the rods are of
dissimilar metals, corrosion may be a problem, as discussed in Bulletin
1751F-802.

.c.:**5.9** **[Protectors Not Near Electric Service
Ground]{.underline}**;: Where conditions are such that the only location
the primary protector can be installed is away from the power service
grounding system, installation of the primary protector may be
accomplished by: (1) attaching the primary protector grounding conductor
to a ground rod driven as close as is practicable to the primary
protector installation site as described in Paragraph 5.5.1.5, and (2)
bonding the telecommunications ground rod to the electric system
grounding system (i.e., power grounding conductor, grounding electrode,
metallic conduit covering the power grounding conductor, etc., \[see
Paragraph 5.5.1.1\]) using at least a #6 AWG conductor. A water pipe may
be utilized in the bonding but the #6 AWG bonding conductor has to be
attached to the water pipe within 5 feet (1.52 meters) of where the pipe
enters the building. Oftentimes, it is more practical to attach the
#6 AWG bonding conductor all the way to the electrical grounding system
grounding conductor, grounding electrode, etc.

.c.:**5.10** **[Section 250 of the NEC]{.underline}**;: NEC Section 250,
on grounding, includes information concerning bonding and grounding of
the power system at the subscriber\'s premises. It stresses the
interconnection of available grounds at the premises to form a grounding
electrode system in order to prevent hazardous differences in potential
between the various systems. It is primarily the subscriber\'s
responsibility to see that bonding between the [electric
service]{.underline} driven electrode and the water system is provided
by an electrician. If this bond is not installed, the subscriber should
be notified and requested to have it installed. If the subscriber is
unwilling to have this bond installed by an electrician, the
telecommunications grounding electrode should be bonded to somewhere on
the power grounding system and bonding of the water pipe should be
included as part of the [telecommunications installation]{.underline}.
RUS recommends that in such circumstances that the installer be a
certified electrician acceptable to the AHJ. In most areas of the
country, the electric service grounding electrode and grounding
conductor are part of the house wiring installation and are the property
of the subscriber. It is, therefore, not normally necessary to obtain
permission of the power distribution company before bonding to it.

**5.10.1** **[Power Grounds Away From Buildings]{.underline}**: A note
of caution is necessary for access to power system grounding at other
than what is available inside or just outside the external wall of a
building or home. Except in the case of mobile home installations (see
Section 6 of this bulletin), Article 800 of the NEC intends that primary
protector grounding conductors be attached to the nearest accessible
point on the power grounding system (see Paragraph 5.5.1.1) that is
related to the [power service means or main disconnecting means for the
building or home]{.underline}. Power grounding means at poles and other
sources away from the building or home, such as at curb side locations,
are not acceptable sources for telecommunications primary protector
grounding. These grounding sources are remote sources with respect to
the grounding source established (and required by the NEC) at the
building being served. Because they are remote grounding sources, they
could expose telecommunications customers to hazardous potential
differences that may appear across the power grounding means established
at the building power service or disconnecting means and the remote
telecommunications grounding electrode source chosen away from the
building or home. Because of this possible hazard, RUS recommends that
such grounding sources not be used for primary protector grounding. If
the AHJ mandates that the telephone company serve a customer and
establish the demarcation point at such a remote location, RUS
recommends that the telephone company install a primary protector at the
remote location. RUS also recommends that final connection to the
customer owned drop and telecommunications facilities not be completed
until the customer presents the telephone company with evidence of the
AHJ\'s certification that the customer\'s facilities comply with the NEC
or local code requirements.

.c.:**5.11** **[Multipair Fuseless Primary Protectors]{.underline}**;:
Multipair primary protectors include a common grounding bar as an
integral part of their mounting. Where such a bar is furnished, two or
more fuseless primary protectors should be grounded by connecting an
insulated copper wire (gauge shown in Table 1) from the grounding
electrode to the grounding terminal on the protector assembly.

**.t.Table 1 Grounding Wire Gauge for Fuseless Protectors;**

**(Number of Pairs) Grounding Conductor**

**FUSELESS FUSED Gauge (AWG)**

**1 to 2 1 to 3 12**

**3 to 5 4 to 7 10**

**6 OR MORE 8 or more 6**

.c.**6. GROUNDING AND BONDING - MOBILE HOMES AND TRAILERS**;

.c.:**6.1** **[Protection of Mobile Homes]{.underline}**;: Mobile home
and trailer installations present certain problems not encountered in
permanent buildings. As in other installations, it is desirable for
access that the primary protector be installed outdoors. However,
mounting of a primary protector on the trailer body is usually
objectionable to the owner, and other methods have to be employed. (See
RUS Bulletin 345-52).

.c.:**6.2** **[Primary Protectors]{.underline}**;: Protection for mobile
homes involves the use of standard primary protectors preferably of the
fuseless type where the provisions of the NEC can be observed.

.c.:**6.3** **[Preferred Primary Protector
Installation]{.underline}**;**:** The RUS preferred method for
installing a primary protector at a trailer (or mobile) home involves
extending buried plant from the main distribution cable to a
pedestal─mounted terminal housing within 1 foot (30.5 cm) from the
outside wall of the trailer to be served. The primary protector is
grounded to an 8 foot (2.5 m) driven ground rod using a \"Listed\"
grounding conductor of at least 12 AWG. The frame of the trailer is also
bonded to the driven ground rod using at least a 6 AWG, insulated,
copper, conductor. If the power service disconnecting means is within
35 feet (10.7 m) of the trailer, the telecommunications ground rod is to
be bonded to the power service grounding system using at least a 6 AWG,
copper, conductor. (The 6 AWG conductor \[bond\] from the
telecommunications company driven ground rod to the grounding electrode
at the power service disconnecting means should be insulated unless it
is buried and not exposed to possible human contact throughout its
entire length.) If the power service disconnecting means is more than
35 feet (10.7 m) away from the trailer, the telecommunications ground
rod does [not]{.underline} have to be bonded to the power service
grounding system. For additional details see Figures 3 and 4.

.c.:**6.4** **[Another Installation Method]{.underline}**;: The NEC
allows utilities to install telecommunications primary protectors at
mobile homes in a manner which differs from RUS\' preferred method. The
code allows the primary protector to be installed adjacent to the power
disconnecting means or power service equipment means serving a mobile
home. However, this code allowance includes a number of provisos which
require significant site and power installation evaluation on the part
of the telecommunications installer; some of this evaluation may be
impossible to determine because facilities are buried or out of sight.
Even if all factors favor installing a primary protector at the power
equipment location, there is still the problem of how and what type
cable/wire to use beyond the protector and how to make the transition to
station wire to serve the customer. Each installation would present
problems. RUS prefers the installation method described in Paragraph 6.3
because it involves minimal assessment of the power facility and all
installations are the same (standardized) except for the bonding to the
power grounding means (i.e., there is either a bond or there is not a
bond).

.c.**7. AC POWER SERVICE PROTECTION;**

.c.:**7.1** **[Equipment Damage]{.underline}**;: With the ever
increasing customer use of data equipment, key systems, PABX\'s,
telephone answering devices, computers (via modems), burglar and fire
alarm systems with telecommunications data connections, and other
subscriber telecommunications equipment powered by 6O Hz ac power,
telephone companies have a greater need to be in a position to offer
customers guidance in preventing equipment damage caused by surges.

**7.1.1** **[Common Bonding of Electrodes]{.underline}**: The first line
of defense for protecting this type of customer premises equipment is to
provide common grounding and bonding as described in Paragraph 2.3.

**7.1.2** **[Severe Exposure Situations]{.underline}**: In severe
exposure situations, such as high lightning damage probability areas
shown in RUS Bulletin 1751F-801 or locations with a history of power
system faults, common grounding and bonding alone may not provide
adequate protection. In such circumstances, protection should be
supplemented by providing additional surge protection to both the ac
power and the telecommunications facilities.

.c.:**7.2** **[Protection of AC Power Service]{.underline}**;: A two
step approach of implementation should be employed when protection of
the telecommunications and power facilities is warranted at a premises:

**7.2.1** **[Step One]{.underline}**: If experience proves special
measures are warranted, telephone companies should advise their customer
to install a secondary power arrester. The secondary arrester should be
installed as close as practicable to where the ac power conductors enter
the premises, usually at the power overcurrent protection device (main
circuit breaker box, etc.,) or alternatively at the service weatherhead
on the subscriber\'s premises. (Examples of acceptable secondary
arresters may be found under the Item \"gi\" listing of RUS
Informational Publication 344-2, \"List of Materials Acceptable for Use
on Telecommunications Systems of RUS Borrowers.\") Harmful surges in the
power supply are first intercepted by the secondary arrester and only
remnant parts of the incoming surge travel on through to connected
electrical equipment inside the premises. With certain types of
secondary arresters, a minimum of 20 feet (6 meters) of steel conduit
between the secondary arrester and the branch circuit panel is required
so that there is sufficient inductance for the proper operation of the
arrester. The installation of a secondary arrester should help to
protect all electrically powered equipment on the subscriber\'s
premises. The secondary arrester should be installed by a qualified
electrician. [In no case should telephone company personnel or the
subscriber be expected to install the secondary arrester]{.underline};
and

**7.2.2** **[Step Two]{.underline}**: In addition to the secondary power
arrester, telephone companies should recommend to their customers that
[customers]{.underline} install, at a minimum, a listed
telecommunications secondary protector on the customer equipment and a
listed power service protector at the electrical outlet from which the
customer equipment is to be energized. The power service protector
should be installed as close to the ac powered telecommunications
equipment as practicable, see Figure 5, \"Typical Power Service
Protector Installation.\" (Examples of acceptable power service
protectors may be found under the Item \"gg\" listing in RUS
Informational Publication 344-2, \"List of Materials Acceptable for Use
on Telecommunications Systems of RUS Borrowers.\" Telecommunications
secondary protectors should comply with Section 800─32 of the NEC and
should be \"Listed\" by an organization which is acceptable to the AHJ).
It is extremely important that the telecommunications secondary
protector grounding terminal and the power service protector grounding
terminal be connected to the same grounded source, with the power
receptacle ground at the installation site being the best choice.
Telephone companies should additionally recommend to customers that if
the protection method to be employed by the customer includes other than
plug─in types of equipment that the customer have the installation made
by a qualified electrician.

**7.2.2.1** **[Recommended Alternative]{.underline}**: A
[recommended]{.underline}, preferred, alternative would be that the
telephone company advise the customer to connect the telecommunications
equipment to a \"Listed\" device that is designed specifically for this
type of protection and which incorporates both the power service
protector and the telecommunications secondary protector within the same
device enclosure and which commonly bonds the grounding of both types of
protectors within the device enclosure.

.c.:**7.3** **[Protector Coordination]{.underline}**;:

**7.3.1** **[Telecommunications Protector Coordination]{.underline}**:
Customers should be advised to consult with the telecommunications
secondary protector manufacturer regarding proper coordination of the
telecommunications secondary protector with the telecommunications
primary protector. The clamping voltage of the telecommunications
secondary protector should be chosen to properly coordinate with the
clamping voltage of the telephone company\'s primary protector. In usual
telecommunications wiring there is sufficient wiring impedance at the
effective frequency of surge related events for the telecommunications
secondary protector to have a lower clamping voltage than the primary
protector; however, extremely low values may be detrimental to service
because excessively frequent operation may effectively cause
objectionable disruption of communications. Consultation with the
protector manufacturer should help in making effective choices.

**7.3.2** **[Power Protector Coordination]{.underline}**: Customers
should be advised to consult with the power service protector
manufacturer regarding proper coordination of the power service
protector with the power secondary arrester. The clamping voltage of the
power service protector should be chosen to properly coordinate with the
clamping voltage of the power secondary arrester. In usual power mains
wiring there is [in]{.underline}sufficient wiring impedance at the
effective frequency of surge related events and it is better for the
power service protector to have a lower clamping voltage than the power
secondary arrester. Coordination will help to prevent the protectors
installed deep within the premises from always clamping first when
reacting to surges and drawing current into the premises wiring when the
first line of defense could react and clamp the surges to ground and
prevent unnecessary current flow in the inside wiring. Consultation with
the protector manufacturer should help in making effective choices.

.c.:**7.4** **[Power Company Practices]{.underline}**;: Power company
practices regarding secondary arresters vary considerably. In most
cases, installation of a secondary arrester at the weatherhead of the
subscriber\'s service would require temporary de─energization of the
secondary circuit serving the service. It is, therefore, essential that
all installations of secondary arresters be coordinated with the power
company involved. In some instances the power company may recommend that
the secondary arrester be installed at the customer\'s load center
instead of at the weatherhead. In other instances the power company may
recommend the use of aluminum or plastic conduit, or possibly
[no]{.underline} conduit instead of the steel conduit. These
alternatives should be approached with caution as many secondary
arresters rely on the reactance of the steel conduit to develop
sufficient voltage drop to cause the arrester to operate. If the steel
conduit is not employed coordination between the secondary arrester and
protected equipment becomes more important and should be addressed.

.f.Figure 1 Example Without Common Grounding;

.f.Figure 2 Example With Common Grounding;

.f.Figure 3 Mobile Home with Bond to Power;

.f.Figure 4 Mobile Home Without Bond to Power;

.f.Figure 5 Typical Power Service Protector Installation;

[^1]: All references to the National Electrical Code in this document
    pertain to the 1993 edition. Readers are urged to refer to the
    edition of the NEC and any, more stringent, local codes adopted by
    their AHJ.