Modern Residential Wiring, 10th Edition Page 169 (169 of 364)

Chapter 10 The Service Entrance
169
Copyright Goodheart-Willcox Co., Inc.
is sized correctly for a residence, the total load
should be calculated based on the various
circuits of the dwelling. A simple series of
calculations can help you fi nd this total load.
See Figure 10-8. Detailed information on these
calculations will be presented in Chapter 12,
Branch-Circuit, Feeder, and Service Design.
Service Entrance
Conductors
Service entrance conductors may be type
RHH, THW, THWW, XHHW, or RHW. They
can be run through conduit or enclosed in a
cable assembly called service entrance cable,
Figure 10-9. Many service drop installations are
made with triplex cable, Figure 10-10.
Service drop
Service entrance conductors
inside conduit
Gutter
Up to 6 disconnects
Taps
Figure 10-6. A maximum of six disconnects are permitted to be installed at the service entrance. All of these
disconnects must be grouped together at a single location.
Service entrance conductors
Service head
Service drop
Meter
Figure 10-7. Service conductors run along the exterior
of a building or are encased in 2″ of concrete within
the building. These conductors should terminate at
the disconnect or service protection equipment close
to where they enter the building or leave the concrete
enclosure.

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Chapter 10 The Service Entrance
169
Copyright Goodheart-Willcox Co., Inc.
is sized correctly for a residence, the total load
should be calculated based on the various
circuits of the dwelling. A simple series of
calculations can help you fi nd this total load.
See Figure 10-8. Detailed information on these
calculations will be presented in Chapter 12,
Branch-Circuit, Feeder, and Service Design.
Service Entrance
Conductors
Service entrance conductors may be type
RHH, THW, THWW, XHHW, or RHW. They
can be run through conduit or enclosed in a
cable assembly called service entrance cable,
Figure 10-9. Many service drop installations are
made with triplex cable, Figure 10-10.
Service drop
Service entrance conductors
inside conduit
Gutter
Up to 6 disconnects
Taps
Figure 10-6. A maximum of six disconnects are permitted to be installed at the service entrance. All of these
disconnects must be grouped together at a single location.
Service entrance conductors
Service head
Service drop
Meter
Figure 10-7. Service conductors run along the exterior
of a building or are encased in 2″ of concrete within
the building. These conductors should terminate at
the disconnect or service protection equipment close
to where they enter the building or leave the concrete
enclosure.

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168
Section 2 Installation
Copyright Goodheart-Willcox Co., Inc.
• If different voltages and phases may be
required within the same structure, addi-
tional services are allowed.
Number of Service
Entrance Conductor Sets
Since the basic rule is that each building will
have only one service drop or service lateral,
the usual service installation will have only one
set of service entrance conductors. Necessary
exceptions include multiple occupancies, such
as two-family homes, apartment buildings, and
commercial establishments with several offi ces
or stores. These occupancies may have any
number of service entrance sets tapped from
a single service supply, Figure 10-5. The NEC
permits a maximum of six disconnects from any
single service drop or service lateral. Figure 10-6
illustrates a possible installation of this nature.
Regardless of the number of service drops,
laterals, or sets of service entrance conductors,
the service should be carefully planned so that
the service entrance conductors are not routed
through the building interior unless encased
in concrete. The service entrance conductors
should also terminate at the disconnect outside
or close to where they enter the structure. See
Figure 10-7.
Service Load
For new single-family dwellings, the NEC
requires at least a 100 A service. For homes
with electrical heating systems or where future
expansion is likely, 150 A or 200 A service is
preferred. However, to be sure that the service
Single service
drop
Service drop
continued along
exterior of building
Common metering
equipment
Individual disconnects
located in each occupancy
Service entrance conductors
installed on building
exterior to each occupancy
Figure 10-5. Multiple occupancies may have any number of service entrance conductors tapped from a service
drop or service lateral.

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170
Section 2 Installation
Copyright Goodheart-Willcox Co., Inc.
Figure 10-8. Use these steps for calculating the total service load.
Conductors
Rubber or
plastic covering
Other insulation
Rubber
Stranded
bare neutral
Outer covering
Twist into
one conductor
Figure 10-9. Service entrance cable (SEC). Bare,
stranded neutral wire must be twisted into a single
strand before being connected.
Figure 10-10. Most service drops in new homes are
made with triplex cable. It consists of a bare neutral wire
around which two insulated cables are loosely wrapped.
The neutral wire supports the insulated wires.

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Page 14Section 1 Fundamentals click to expand contents

Page 70Section 2 Installation click to expand contents

Page 190Section 3 Planning click to expand contents

Page 234Section 4 Specialized Installations click to expand contents

Page 300Section 5 The Professional Electrician click to expand contents

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