Carpentry in Commercial Construction

Carpentry in Commercial Construction

Construction Codes & Inspection Handbook

Construction Codes & Inspection Handbook

Commercial Electrical Wiring to the 1999 NEC

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.

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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.

More Information
Page Count320
AuthorJohn E.Traister
PublisherCraftsman Book Company
Dimensions8-1/2 x 11

Commercial Electrical Wiring
by John E.Traister


Preface, 5

Chapter 1
Introduction, 7
Small Commercial Occupancy, 7
Medium Commercial Building, 9
Chapter 2
The National Electrical Code, 13
NEC Terminology, 14
Learning the Layout of the NEC, 17
Using the NEC, 20
Definitions, 22
Testing Laboratories, 22
Chapter 3
Commercial Construction Documents, 27
Electrical Drawings, 31
Print Layout, 33
Drafting Lines, 37
Electrical Symbols, 38
Scale Drawings, 41
Drawing Schedules, 54
Electrical Details and Diagrams, 54
Schematic Diagrams, 56
Written Specifications, 57
Chapter 4
Electrical Load Calculations, 63
Basic Calculation Procedures, 64
Commercial Occupancy Calculations, 67
Mobile Home and RV Parks, 75
Restaurants, 81
Services for Hotels and Motels, 83
Optional Calculation for Schools, 83
Marinas and Boatyards, 84
Chapter 5
Electric Service, 85
Electrical Distribution, 86
Service Components, 93
Service-Entrance Conductors, 97
Three-Phase Services, 103
480/277-Volt Services, 107
Switches, Panelboards and Load Centers, 108
Chapter 6
Grounding, 119
Types of Grounding Systems, 119
OSHA and NEC Requirements, 121
Earth Electrodes, 125
Grounding Conductors, 127
Equipment Grounding, 128
Grounding Enclosures, 132
Ground-Fault Circuit-Interrupters, 134
Chapter 7
Overcurrent Protection, 139
Circuit Breaker Ratings, 140
Interrupting Capacity Rating, 142
Fuses, 149
Cartridge Fuses, 151
NEC Regulations, 158
Chapter 8
Transformers, 165
Transformer Taps, 168
Transformer Connections – Basic, 169
Autotransformers, 173
Transformer Connections -- Dry Type, 174
Buck-and-Boost Transformers, 178
Control Transformers, 181
Potential and Current Transforrmers, 182
NEC Requirements, 183
Transformer Grounding, 187
Chapter 9
Wiring Methods, 191
Cable Systems, 191
Instrumentation Control Wiring, 198
Raceway Systems, 199
Conductors for Raceway Systems, 203
Properties of Conductors, 205
Conductor Protection, 208
Chapter 10
Raceways, Boxes and Fittings, 215
Conduit Fill Requirements, 215
Installing Conduit, 218
Cutting, Reaming and Threading Conduit, 228
Joining Conduit, 230
Conductors in Conduit, 234
Chapter 11
Wiring Devices, 235
Receptacles, 235
Locating Receptacles, 242
Switches, 246
NEC Requirements for Switches, 248
Safety Switches, 249
Chapter 12
Electrical Lighting, 253
Troffers, 253
Fluorescent Fixtures, 257
Incandescent Lighting, 259
Offices and Schools, 259
Calculating Illumination Levels, 261
Store Lighting, 268
Chapter 13
Electric Motors, 271
Nameplate Information, 271
Single-Phase Motors, 273
Polyphase Motors, 276
Motor Enclosures, 277
Motor Types, 278
Selection of Electric Motors, 279
NEC Requirements, 279
Motor Installation, 280
Chapter 14
Motor Controllers, 283
Types of Motor Controllers, 283
Magnetic Controllers, 287
Power Circuits in Motor Starters, 291
Overload Protection, 292
Selecting Overload Relays, 293
Chapter 15
Special Occupancies, 295
Class I Locations, 295
Class II and III Locations, 298
Prevention of External Ignition/Explosion, 298
Explosionproof Equipment, 299
Explosionproof Conduit and Fittings, 300
Garages and Similar Locations, 307
Airport Hangers, 310
Manufacturer's Data, 312
Index, 313

Commercial Electrical Wiring
byJohn E. Traister


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.


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:

  1. Type of general building construction.
  2. Is the installation a part of a new building or a modernization of an existing one?
  3. Type of ceiling, wall, and floor construction, dimensions, and the like.
  4. Wiring methods.
  5. Location of service, overhead or underground?
  6. Location of service-entrance equipment.
  7. Size of service and feeders and sizes and types of service-entrance equipment and panelboards.
  8. Wiring of windows and display cases.
  9. Type and installation requirements of lighting fixtures. Physical dimensions and construction of recessed lighting fixtures.
  10. 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.


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:

  1. Type of building construction, that is, masonry, reinforced concrete, wood frame, and the like.
  2. Type of floor, ceiling, and partition construction, height of ceiling, space above ceiling, space under floor and the like.
  3. Wiring methods, type of raceway, sizes of conductors.
  4. Type of service-entrance equipment.
  5. Type of service and location of service conductors.
  6. Connections for equipment not furnished by the electrical contractor but requiring electric service.
  7. Type and construction of lighting fixtures, hangers, and supports affecting assembly and installation. Types of lamps.
  8. Type and dimensions of floodlighting supporting poles, floodlights and mounting brackets, and so on.
  9. 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.

cbc_logo.gif (654 bytes) Commercial Electrical Wiring
by John E. Traister

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.

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.