Commercial Electrical Wiring to the 1999 NEC: Overview
by John E. Traister
Make the transition from residential to commercial electrical work. Here are wiring methods, spec reading tips, load calculations and everything you need for making the transition to commercial work: commercial construction documents, load calculations, electric services, transformers, overcurrent protection, wiring methods, raceway, boxes and fittings, wiring devices, conductors, electric motors, relays and motor controllers, special occupancies, and safety requirements. This book is written to help any electrician break into the lucrative field of commercial electrical work.
Most
residential electricians want to move up in the ranks of the profession. Many of
them dream of going into commercial electrical work. Everyone hears the stories
about the big money contracts and the jobs that run for months at a stretch. On
a commercial job you can run at assembly-line speed, and not face the constant
delays of change orders so common in residential work. If you think this sounds
like an electrician's paradise, this book will help you get there.
Make
no mistake, commercial electrical work is different. That's exactly why
so few residential electricians do anything more than daydream about turning to
commercial work. One big hurdle is having to learn the sections of the National
Electrical Code specific to commercial work. This book is filled with
explanations, examples and tips to help you comply with the parts of the code
that are new to you. Lists of crucial parts of the requirements appear
throughout the book. These special sections cover:
-
Grounding
-
Switches
-
Overcurrent protection
-
Electric motors
Another
big difference between residential and commercial electrical work is the greater
complexity and volume of paper. An electrician who's not prepared is easily
overwhelmed by it all. This manual prepares you for this by showing you how to
read and understand any unfamiliar symbols, plans, drawings, diagrams, or
schematics. It will also guide you through the pages and pages of specifications
common in commercial electrical work
The
usefulness of this book won't end when you're off and running with new
commercial jobs. You'll want to keep it close at hand on job sites because of
all the practical information included here:
-
Sizing of electrical services and conductors
-
Placement and configuration of wiring devices
-
Selecting and installing the right overcurrent protection
-
Load calculation formulas and examples
-
Commercial wiring systems of all types
-
Safety and support systems
If
you're an electrician who wants to increase your work volume and profits by
moving into commercial work, Commercial Electrical Wiring will show you
the way.
About The Author
John
Traister has more than thirty years in the construction business to his
credit. Licensed as a master electrician in Virginia, he's done both electrical
design and installation on a broad spectrum of commercial and residential
projects. He was a principal in
Engineering Associates, Ltd., where his responsibilities included
supervising other electrical designers and keeping them abreast of changes in
the National Electrical Code. It was a logical next step to bring his
skills and experience together as a writer of technical manuals. He has shared
his knowledge of commercial electrical design and installation and the NEC with
an ever-widening audience, in almost 100 technical books and nearly 300 articles
published in a mix of trade journals and nationally-distributed publications.
Commercial Electrical Wiring to the 1999 NEC: Introduction
Preface
Building construction in the United States alone
has reached over $300 billion a year and continues to grow at a phenomenal rate,
because the population proliferation demands new living, working, and
recreational facilities. A good percentage of this building construction work
involves electrical installations.
While many
electricians begin their careers wiring residential occupancies (especially
those entering the electrical contracting business), there will eventually come
a time when these same electricians (or contractors) will want to jump into
larger commercial construction projects.
There is another
large group of electrical workers that begins apprenticeship training in large
industrial establishments, perhaps working for months or years on one
comparatively small part of a huge, complex electrical network. In fact, the
larger electrical contractors in the United States frequently bid electrical
projects valued at $200 million or more. Most industrial electrical workers will
feel "out of place" should they be required to undertake a smaller
commercial electrical installation. Most will require some initial training to
acquaint them with the different wiring techniques, NEC requirements, and
installation methods.
There are
numerous books available on the study of basic electricity and electrical wiring
in general. Few, however, are aimed directly at commercial electrical wiring -
the type of electrical construction that uses the most electricians, the
greatest amount of materials, and for which the greatest amount of working
drawings and specifications are prepared. This book, Commercial Electrical
Wiring, is designed to help this situation.
The intent of Commercial
Electrical Wiring is to dwell only briefly on introductory material and
theories. We quickly jump into practical, on-the-job applications that are used
for almost all types of wiring systems for commercial buildings. Furthermore,
this book is designed in such a way as to help residential or industrial
electrical workers make the transition to commercial wiring methods as smoothly
as possible, eliminating much of the field trial-and-error method. Consequently,
experienced electrical workers will not have to reinvent the wheel when making
the transition.
This book is
also designed as a practical study guide for electrical trainees, apprentices,
and others who are associated with commercial wiring systems in any capacity -
providing guidance in simplified form, and usable at many educational levels.
In
summary , this book is a quick reference for those actively engaged in
commercial wiring, a learning method for those entering the commercial
electrical field from another branch of the electrical construction industry ,
and a refresher for those electrical workers with wide experience in the field.
I
would like to thank my own staff who so willingly and enthusiastically
contributed their time and experience to this project - validating data and
providing excellent and meaningful illustrations throughout the book.
John
E. Traister
Chapter 1 Introduction
Electrical
wiring systems for commercial buildings can vary considerably - from a few
lighting fixtures and a couple of convenience outlets for a small, one-room
vegetable stand (Figure 1-1) to extremely complex installations used in
high-rise office or apartment buildings (Figure 1-2). However, in most cases,
commercial buildings may be classified into either small, medium, or large
sizes, with practically an infinite number of uses for each one; for example, a
small building may be used for a real estate office, a roadside produce stand or
a laundromat.
SMALL
COMMERCIAL OCCUPANCY
In planning the
wiring system for a small commercial building - either from a design or
installation standpoint - there are several factors to be considered before
material is ordered and the actual installation takes place.
Some
of the factors that should be considered for small commercial establishments
include the following:
- Type
of general building construction.
- Is
the installation a part of a new building or a modernization of an existing
one?
- Type
of ceiling, wall, and floor construction, dimensions, and the like.
- Wiring
methods.
- Location
of service, overhead or underground?
- Location
of service-entrance equipment.
- Size
of service and feeders and sizes and types of service-entrance equipment and
panelboards.
- Wiring
of windows and display cases.
- Type
and installation requirements of lighting fixtures. Physical dimensions and
construction of recessed lighting fixtures.
- In
the case of a modernization or complete wiring of an existing building, to
what extent may the main service be used, and how much will it have to be
enlarged?
Taking
each of these individually, factor 1 may be determined by the working drawings
(Figure 1-3) and specifications, by a job-site investigation, or by consulting
with the owners. The same is true for factors 2 and 3.
The
wiring method to use (4) may be dictated by the working drawings or
specifications. If not, the wiring method to use should comply with the latest
edition of the National Electrical Code (NEC) and/or local ordinances.
The
location of service equipment (5 and 6) may be indicated on the working drawings
or the local power company may have to be consulted to determine the best
location. Locating the service equipment is often left to the electrician or
contractor to decide, but if working drawings are available, they should be
followed.
Sizing
the electric service (7) requires calculations as discussed in Chapter 5 or the
designer may have indicated the service size on the working drawings.
Lighting
fixtures (9) should be preselected by either the designer, owner, or architect.
Installation details may be found in manufacturers' catalogs. Shop drawings
(Figure 1-4) are usually provided for commercial installations of any
consequence.
Factor
10 can be determined either from the working drawings or by a job site
investigation.
In
general, the designer or electrician performing the work will calculate the
total load for the building, determine the number of branch circuits required
and service-entrance size, along with feeders, service-entrance equipment, and
panel boards. The number of outlets will be determined along with their
location. Illumination levels are calculated and then lighting fixtures are
selected to provide the required illumination.
Continue
by noting connections for any special equipment, such as water heaters or air
conditioners. Also determine the requirements for any security/ fire-alarm
system, display case connections, and the like.
Determine
the lengths of all branch circuits, service, and feeder runs and list the wire
size for each. Account for service-entrance equipment and any other major pieces
of equipment requiring electrical connections.
The
preceding information should provide a good summary of the material needed for
the job to be used in estimating costs and the number of men required for the
installation and to aid in ordering the required material.
In
most cases, small commercial projects utilize rigid steel conduit for the
service-entrance regardless of whether it is overhead or underground. Check with
the local power company to find out exactly what is required of the contractor
or electricians doing the work. Either rigid or EMT conduit is used for all
wiring below grade and embedded in concrete slabs. Either EMT or type AC cable
is normally used for wiring above grade.
Be
extremely careful of any wiring that may be installed in hazardous locations,
such as in commercial service stations around the gas pumps and in the garage
area.
One
main point of concern with this type of project, as well as with most other
electrical installations, is to plan the job well so as to perform the work in
the shortest possible time, yet keep the quality high and in a workmanlike
manner. Other trades should not be held up in performing their work, and the
electrical workers must plan and work accordingly. For example, before the
concrete floor may be poured and finished, all conduit, boxes, and fittings must
be installed by the electricians. When the ground is graded, wire mesh
installed, and the like, the electrical workers usually have only a certain
amount of time to complete their portion of the work. Make certain all necessary
material is at hand on the job site well before the installation will take
place. Have the working drawings or at least a sketch at hand to go by, and work
efficiently when the time comes. Also double-check each homerun, circuit, and
outlet box location, as once the cement is poured, it would be quite costly to
make any changes under it.
At
least one electrician should be present during the pouring to ensure that none
of the electrical system is damaged; if it is, the damage should be corrected
immediately before the concrete sets up.
MEDIUM
COMMERCIAL BUILDING
A
medium-sized commercial occupancy is planned much like the smaller building just
described, except there will be more circuits, a larger service entrance, and so
on. In nearly all cases, working drawings will be provided by an
architectural-engineering firm to consult during the job. If engineer's drawings
are not provided, the electrical contractor should provide some type of layout
to be followed. Not only do such drawings aid the workers as the job progresses,
but they also give a means of knowing what has been installed at a later date
while the building's electrical system is being maintained or repaired.
Depending
on the use of the building, the NEC or local ordinances may require a
different wiring method than would be required in a smaller building.
Most
larger commercial buildings utilize a 480/277-volt Y-connected service entrance;
all heavy equipment, such as compressors for air conditioning, are designed for
use on 480 volts; electric discharge
lighting is all designed for operation on 277-volt, single-phase circuits; dry
transformers are required to obtain 120 volts for convenience outlets; and other
outlets use 240 and/or 120 volts.
Factors
affecting wiring systems in large commercial buildings include the following:
- Type of
building construction, that is, masonry, reinforced concrete, wood frame,
and the like.
- Type of
floor, ceiling, and partition construction, height of ceiling, space above
ceiling, space under floor and the like.
- Wiring
methods, type of raceway, sizes of conductors.
- Type of
service-entrance equipment.
- Type of
service and location of service conductors.
- Connections
for equipment not furnished by the electrical contractor but requiring
electric service.
- Type and
construction of lighting fixtures, hangers, and supports affecting assembly
and installation. Types of lamps.
- Type and
dimensions of floodlighting supporting poles, floodlights and mounting
brackets, and so on.
- Ground
conditions affecting trenching for parking lot lighting.
The majority of
the factors can be determined by examining the working drawings and
specifications, as any commercial building of this size will have a detailed,
engineered set of drawings and specifications. If not, the contractor will have
to have the system designed and working drawings made to aid the workers on the
job. Building inspectors often also require that they be supplied with at least
one set of drawings and specifications for use in their office and to check
against the actual installation.
In many cases,
it is also a good idea for the contractor to examine the job-site conditions
prior to bidding or beginning the electrical installation.
A complete
take-off of materials will be required for this size of installation for the
purpose of estimating the cost of construction, as well as for ordering material
and scheduling it for use at the job site.
In many
instances, consulting engineers will prepare drawings that leave out much
detail, requiring the contractor or his personnel to do extensive research to
determine exactly what is taking place. For example, a main distribution
panelboard may be indicated on the drawings only by a symbol on the floor plan
layout and a catalog number of the equipment. A better drawing, however, will
have a complete power riser diagram to supplement the floor plan drawing,
showing conduit sizes, wire sizes, number of conductors, and so on. The person
installing the system, when only meager symbols are used, usually will have to
make a rough layout of the installation and list all details before materials
can be ordered or the installation started. Calculations will have to be
performed to determine wire size, limit voltage drop, size of conduit, and the
like. All these details should be worked out prior to starting the electrical
installation.
While commercial
electrical installations may vary considerably in detail, in general the
majority of them will follow a definite pattern. For example, each will have a
service entrance, a distribution panelboard, lighting, and convenience outlets.
Furthermore, nearly all will have emergency lighting and signal systems. All
will have branch circuits, feeders, and the like.
Therefore, when
the electrical technician is called on to design or install a commercial
electrical installation, there should really be no "strange" jobs once
he or she has worked on a few commercial installations. Then, by following sound
basic planning techniques and giving careful attention to details, the trained
technician should never be completely stumped, even on jobs of a type that have
not been previously handled. A
certain amount of research will have to be done on all electrical jobs. Even
seasoned professionals constantly refer to reference material for practically
every new project. For example, while the professional engineer may remember the
required footcandle level of, say, an office area, he or she will have to refer
to manufacturers' catalogs to obtain the illuminating characteristics of certain
lighting fixtures. Tables will be consulted to determine voltage drop on various
sizes of wire over a given distance and carrying a certain load. Short-circuit
calculations will be made to specify the required overcurrent protection -just
to name a few. However, the pattern or sequence in which these unknowns are
determined is practically the same on every commercial job.
Workers on the
job have a further responsibility. While the better engineered drawings and
specifications are coordinated to a certain extent with the architectural
drawings and the work of other trades, none can be absolutely complete all the
time. It is up to the workers on the job to be sure that conduit runs will not
interfere with the equipment of other trades. Furthermore, they must make
certain that the electrical equipment will not weaken the structural members of
the building. The electricians are also required to layout the circuit runs to
use the least amount of material, yet see that the finished job is done in a
professional manner.
Sometimes it
becomes necessary to vary from the working drawings considerably during the
installation, but before doing so, the consulting engineer or architect should
be consulted for approval.
In summary,
regardless of the technician's position - designer, electrician, supervisor, or
whatever - a certain amount of planning is required on all commercial electrical
installations. This planning is begun, before any work is started, and then
continues on a day-to-day basis until the project is completed. Then a certain
amount of planning is required to perform the final tests of the entire system.
Even on projects
with detailed engineered drawings and specifications, planning and coordination
during the construction phase are still necessary. Certain phases of the
electrical installation will have to be carefully planned so as not to hold up
any other trades from doing their work. Local inspectors will have to be
notified at certain times so that they can inspect the work before it is covered
up. Material and tools will have to be ordered so that they will be on the job
site when needed. The design group will have to make periodic checks to ensure
that the equipment specified is in fact being used, while the workers or the
foreman on the job will have to make certain that installed equipment is not
damaged by other trades while performing their respective work.
While other
factors beyond your control may adversely affect the final electrical
installation, job planning and carrying out this plan are largely the basis on
which the work will be performed. Be certain that the planning is done on a
sound basis.
Your Shopping Cart:
