Electrical Level 3 Trainee Guide

538 Pages·2017·413.479 MB·English

by  NCCER

Acknowledgments
This curriculum was revised as a result of the farsightedness and leadership of the following sponsors:
ABC of Iowa ISC Constructors, LLC
ABC Northern California Chapter Lamphear Electric
ABC Southern California Chapter Lee College
Beacon Electrical Contractors Madison Comprehensive High School
Cianbro Corporation Pro Circuit, Inc.
Faith Technologies, Inc. Putnam Career and Technical Center
Gaylor Electric, Inc. Specialized Services
Harbor Energy Solutions Tri-City Electrical Contractors
Industrial Management and Training Institute, Zenith Education Group
Inc.
This curriculum would not exist were it not for the dedication and unselfish energy of those volunteers
who served on the Authoring Team. A sincere thanks is extended to the following:
Chuck Ackland L.J. LeBlanc Raymond Saldivar
Tim Dean David Lewis Greg Schuman
Tim Ely John Lupacchino Joshua Simpson
Ronnie Gulino Scott Mitchell Wayne Stratton
Justin Johnson Todd Moody Marcel Veronneau
Robert Kolb John Mueller
Dan Lamphear Mike Powers
NCCER Partners
American Council for Construction Education Prov
American Fire Sprinkler Association SkillsUSA®
Associated Builders and Contractors, Inc. Steel Erectors Association of America
Associated General Contractors of America U.S. Army Corps of Engineers
Association for Career and Technical Education University of Florida, M. E. Rinker Sr., School of
Association for Skilled and Technical Sciences Construction Management
Construction Industry Institute Women Construction Owners & Executives,
Construction Users Roundtable USA
Design Build Institute of America
GSSC - Gulf States Shipbuilders Consortium NCCER Business Partners
ISN
Manufacturing Institute
Mason Contractors Association of America
Merit Contractors Association of Canada ® ) S( % A C B
NACE International J SORTH AMERICAS CRASE BUREAU, ISC.
National Association of Women in Construction
JUDGMENT INDEX
National Insulation Association
National Technical Honor Society
Q
National Utility Contractors Association Pr&/
NAWIC Education Foundation Pearson
North American Crane Bureau
North American Technician Excellence
Pearson
Contents
Module One Module Five
Load Calculations - Overcurrent Protection
Branch and Feeder
Explains how to size and select circuit breakers
Circuits and fuses for various applications. Also covers
short circuit calculations and troubleshooting.
Explains how to calculate branch circuit and
(Module ID 26305-17; 25 Hours)
feeder loads for various residential and commer­
cial applications. (Module ID 26301-17; 17.5 Hours)
Module Six
Module Two
Distribution Equipment
Conductor Selection and
Discusses switchboards and switchgear, includ­
Calculations ing installation, grounding, and maintenance
requirements. This module also includes electrical
Covers the various factors involved in conductor
drawings of distribution equipment. (Module ID
selection, including insulation types, current-
26306-17; 12.5 Hours)
carrying capacity, temperature ratings, and volt­
age drop. (Module ID 26302-17; 15 Hours)
Module Seven
Module Three T ransf ormers
Practical Applications of Discusses transformer types, construction, con­
Lighting nections, protection, and grounding. (Module ID
26307-17; 12.5 Hours)
Covers specific types of incandescent, fluorescent,
and HID lamps, as well as ballasts, troubleshoot­
Module Eight
ing, and various types of lighting controls. (Mod­
ule ID 26303-17; 12.5 Hours) Commercial Electrical
Services
Module Four
Covers the components, installation consider­
Hazardous Locations ations, and NEC® requirements for various com­
mercial services. (Module ID 26308-17; 10 Hours)
Covers the NEC1 requirements for equipment
installed in various hazardous locations. (Module
ID 26304-17; 15 Hours)
vi
26311-17
Motor Controls
Module Nine LU
26310-17
LU
Motor Calculations Voice, Data, and Video
OC
Covers calculations required to size conductors
26309-17
and overcurrent protection for motor applications.
I Motor Calculations
(Module ID 26309-17; 12.5 Hours)
I-
26308-17
Module Ten Commercial Electrical Services
- I
LU
Voice, Data, and Video 26307-17
> Transformers
Covers installation, termination, and testing of
LU
various voice, data, and video cabling systems.
26306-17
(Module ID 26310-17; 10 Hours) Distribution Equipment
26305-17
Module Eleven
Overcurrent Protection
<
Motor Controls
o 26304-17
Provides information on selecting, sizing, and Hazardous Locations
installing motor controllers. Also covers control DC
circuit pilot devices and basic relay logic. (Module 26303-17
ID 26311-17; 12.5 Hours) IH Practical Applications of Lighting
O
26302-17
Glossary LU Conductor Selection
and Calculations
_ l
LU
Index 26301-17
Load Calculations -
Branch and Feeder Circuits
Electrical Level Two
Electrical Level One
-------
Core Curriculum:
Introductory Craft Skills
This course map shows all of the modules in
Electrical Level Three. The suggested training
order begins at the bottom and proceeds up. Skill
levels increase as you advance on the course
map. The local Training Program Sponsor may
adiustthe trainina order.
vii
nccei Load Calculations - Branch
and Feeder Circuits
Overview
The purpose of branch circuit load calculations is to determine the
sizes of branch circuit overcurrent protection devices and branch
circuit conductors using A/EC® requirements. Sizing loads and
protection devices appropriately ensures safe, reliable electrical
systems. This module explains how to calculate branch circuit and
feeder loads for residential and commercial applications. It also
covers various derating factors.
Trainees with successful module completions may be eligible for credentialing through the NCCER Registry. To learn
more, go to www.nccer.org or contact us at 1.888.622.3720. Our website has information on the latest product releases
and training, as well as online versions of our Cornerstone magazine and Pearson's product catalog.
Your feedback is welcome. You may email your comments to [email protected], send general comments and in­
quiries to [email protected], or fill in the User Update form at the back of this module.
This information is general in nature and intended for training purposes only Actual performance of activities de­
scribed in this manual requires compliance with all applicable operating, service, maintenance, and safety procedures
under the direction of qualified personnel. References in this manual to patented or proprietary devices do not consti­
tute a recommendation of their use.
Copyright © 2017 by NCCER, Alachua, FL 32615, and published by Pearson Education, Inc., New York, NY 10013. All rights reserved.
Printed in the United States of America. This publication is protected by Copyright, and permission should be obtained from NCCER prior
to any prohibited reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photo­
copying, recording, or likewise. To obtain permission(s) to use material from this work, please submit a written request to NCCER Product
Development, 13614 Progress Blvd., Alachua, FL 32615.
From Electrical LevelThree, Trainee Guide, Ninth Edition. NCCER.
Copyright © 2017 by NCCER. Published by Pearson Education. All rights reserved.
26301-17
Load C alculations - Branch and Feeder C ircuits
Objectives ---------------------------------------------------------------------------
When you have completed this module, you will be able to do the following:
1. Calculate branch circuit loads.
a. Calculate branch circuit ratings.
b. Apply derating factors.
c. Calculate branch circuit ampacity.
2. Identify residential branch circuit requirements.
a. Calculate lighting loads.
b. Calculate receptacle loads.
c. Calculate small appliance loads.
d. Calculate laundry circuit loads.
e. Calculate cooking appliance loads.
f. Calculate water heater loads.
g. Calculate electric heating loads.
h. Calculate air conditioning loads.
3. Calculate commercial loads.
a. Calculate the loads on multi-outlet assemblies.
b. Calculate show window loads.
c. Calculate sign loads.
d. Calculate loads for heavy-duty lamp holder outlets.
e. Calculate commercial kitchen equipment loads.
f. Calculate motor loads.
g. Calculate welder loads.
Performance Tasks --------------------------------------------------------
This is a knowledge-based module. There are no Performance Tasks.
Trade Terms --------------------------------------------------------
Ampacity Demand factors Outlet
Appliance Device Overcurrent
Appliance branch circuits General-purpose branch circuits Receptacle
Branch circuit Individual branch circuit Receptacle outlet
Continuous load Multi-outlet assembly Utilization equipment
Industry Recognized Credentials ---------------
If you are training through an NCCER-accredited sponsor, you may be eligible for credentials from
NCCER's Registry. The ID number for this module is 26301-17. Note that this module may have been
used in other NCCER curricula and may apply to other level completions. Contact NCCER's Registry at
888.622.3720 or go to www.nccer.org for more information.
Note ------------------------------------------------------------------------------------------------------------------------
NFPA 70^, National Electrical Code® and NEC® are registered trademarks of the National Fire Protection
Association, Quincy, MA.
Contents --------------------------------------------------------------------------
1.0.0 Branch Circuit Loads.................................................................................................1
1.1.0 Branch Circuit Ratings........................................................................................2
1.2.0 Derating Factors...................................................................................................3
1.2.1 Temperature Derating....................................................................................4
1.2.2 Voltage Drop Derating for Single-Phase Circuits....................................5
1.2.3 Voltage Drop Derating forThree-Phase Circuits...................................7
1.3.0 Branch Circuit Ampacity...................................................................................8
2.0.0 Residential Branch Circuit Requirements.....................................................10
2.1.0 Lighting Loads.....................................................................................................10
2.1.1 Recessed Lighting Loads..............................................................................11
2.2.0 Receptacle Loads................................................................................................11
2.3.0 Small Appliance Loads....................................................................................12
2.4.0 Laundry Circuit Loads.......................................................................................12
2.5.0 Cooking Appliance Loads...............................................................................13
2.6.0 Water Heater Loads...........................................................................................14
2.7.0 Electric Heating Loads......................................................................................14
2.8.0 Air Conditioning Loads....................................................................................16
3.0.0 Commercial Loads.................................................................................................18
3.1.0 Loads on Multi-Outlet Assemblies...............................................................18
3.2.0 Show Window Loads........................................................................................19
3.3.0 Sign Loads.............................................................................................................19
3.4.0 Loads for Heavy-Duty Lamp Holder Outlets...........................................20
3.5.0 Commercial Kitchen Equipment Loads.....................................................20
3.6.0 Motor Loads.........................................................................................................20
3.7.0 Welder Loads.......................................................................................................22
Figures
Figure 1 Calculating a load center length and total load
for multiple fixed loads on a circuit.........................................................6
Figure 2 Welding machines.......................................................................................23
Branch circuits supply utilization equipment.
S ec t io n O ime
Utilization equipment is defined by the NEC® as
equipment that utilizes electric energy.
1.0.0 Branch Circuit Loads NEC Article 210 covers branch circuits (except
for branch circuits that supply only motor loads).
NEC Section 210.3 provides a listing of other
Objective code articles for specific-purpose branch circuits.
Per NEC Section 210.18, branch circuits are rated
Calculate branch circuit loads.
by the maximum rating or setting of the overcur­
a. Calculate branch circuit ratings.
rent device. Except for circuits serving individual
b. Apply derating factors.
utilization equipment (dedicated circuits), branch
c. Calculate branch circuit ampacity.
circuits shall be rated 15A, 20A, 30A, 40A, and
50A. Branch circuits designed to serve individual
Trade Terms loads can supply any size load with no restric­
tions to the ampere rating of the circuit.
Ampacity: The maximum current in amperes
Per NEC Section 210.19(A)(1), branch circuit
that a conductor can carry continuously under
conductors are required to be sized with an am­
the conditions of use without exceeding its tem­
pacity rating that is no less than the maximum
perature rating.
load to be served. Branch circuit overcurrent
Branch circuit: The circuit conductors between
protection is required to have a rating or set­
the final overcurrent device protecting the circuit
ting not exceeding the rating specified in NEC
and the outlet(s).
Section 240.4 for conductors, NEC Section 240.3
Continuous load: A load where the maximum for equipment, and NEC Section 210.21 for outlet
current is expected to continue for three hours
devices including lamp holder and receptacle de­
or more.
vices. NEC Article 430 applies to branch circuits
Device: A unit of an electrical system, other than supplying only motor loads and NEC Article 440
a conductor, that carries or controls electric en­ applies to branch circuits supplying only air con­
ergy as its principal function.
ditioning equipment, refrigerating equipment, or
Individual branch circuit: A branch circuit that both.
supplies only one piece of utilization equipment. Branch circuit conductors must have an ampac­
Outlet: A point on the wiring system at which ity rating equal to, or greater than, the noncon-
current is taken to supply utilization equipment. tinuous load plus 125% of the continuous load
Overcurrent: Any current in excess of the rated before the application of any adjustment or correc­
current of equipment or the ampacity of a con­ tion factors per NEC Section 210.19(A) and (B).
ductor. It may result from overload, short circuit,
or ground fault.
Receptacle: A contact device installed at an out­ To find 125% of a load, multiply it by 1.25. For
let for connection as a single contact device. A example, 125% of a 14A load is 17.5A, since
single receptacle is a single contact device with 14A x 1.25 = 17.5A.
no other contact device on the same yoke. A mul­
Finding a percentage of a load involves
tiple receptacle is a single device containing two
dividing the percentage by 100 (in this example,
(duplex) or more receptacles.
125% -5- 100 = 1.25), and then multiplying the
Receptacle outlet: An outlet where one or more
result by the load value.
receptacles are installed.
Also note that finding 100% of any number
Utilization equipment: Equipment that utilizes results in the same number, since any number
electric energy for electronic, chemical, heating, times 1 is equal to itself. (For example, 100% of
lighting, electromechanical, or similar purposes. 18 = 18 x 1 = 18.)
The purpose of branch circuit load calcula­ NEC Sections 210.23(A) through (D) define
tions is to determine the size of branch permissible loads for multiple-outlet branch cir­
circuit overcurrent protection and branch cuits. This is important information because it
circuit conductors using National Electrical Code®l ists the types of loads that may be served accord­
(NEC®) requirements. When the branch circuit ing to the size of the branch circuit. NEC Section
load is accurately calculated, branch circuit com­ 210.24 and NEC Table 210.24 summarize the
ponents can be sized to serve the load safely. branch circuit requirements.
26301-17 Load Calculations - Branch and Feeder Circuits Module One 1
NEC Article 220 includes the requirements
used to determine the number of branch cir­
Think About It
cuits required and the requirements used to com­
pute branch circuit, feeder, and service loads.
Load Calculations
NEC Section 210.20(A) states that the rating of
a branch circuit overcurrent protection device Which factors need to be taken into consideration
shall not be less than the noncontinuous load when adding a large load to an existing service?
plus 125% of the continuous load. NEC Table
220.12 gives general lighting loads listed by types
of occupancies. These general lighting loads are Branch circuits may supply noncontinuous
expressed as a unit load per square foot in volt- loads, continuous loads, or a combination of the
amperes (VA). two. Per NEC Section 210.20(A), the branch cir­
For example, the unit lighting load for a bar­ cuit rating shall not be less than the noncon­
ber shop is 3VA/ft2, a store is also 3VA/ft2, and tinuous load plus 125% of the continuous load. A
a storage warehouse is ^VA/ft2. NEC Sections continuous load is defined by NEC Article 100
220.14(A) through 220.14(h) list minimum loads as a load whose maximum current is expected
for outlets used in all occupancies—these outlets to continue for three hours or more. Continuous
include general-use receptacles and outlets not loads are calculated at 125% of the maximum cur­
used for general illumination. rent rating of the load.
Local codes may require different values than
The reciprocal of 125% (1.25) is 1/i,25' which
the minimum NECa values. For instance,
is equivalent to 80% of the rating at the
local codes may limit the number of outlets
UJ overcurrent protective device. (I.e., you will
H- on a branch circuit to less than the calculated
get the same result when you divide by 1.25 as
O
value, or they may require dedicated circuits LU
Z h- when you multiply by 0.8.)The reciprocal can be
other than those that are listed in the A/EC®. O
z used to calculate the maximum load that may
Always check local codes before beginning any
be connected based on the circuit rating.This
installation.
means that, in situations where the rating must
be at least 125% of the load, the maximum load
can be calculated by finding 80% of the rating.
1.1.0 Branch Circuit Ratings
The maximum load that a single-phase branch
circuit may serve is determined by multiplying Both NEC Sections 210.19(A)(1) Exception
the rating or setting of the overcurrent protection and 210.20(A) Exception state that, except where
device (circuit breaker or fuse) by the circuit volt­ the assembly is listed for operation at 100% of its
age. For example, the maximum load that may be rating (exception), the allowable ampacity of the
supplied by a 20A, two-wire, 120V circuit is calcu­ branch circuit conductors shall be permitted to be
lated as follows: not less than the sum of the continuous load plus
the noncontinuous load.
20A X 120V = 2,400VA
For 15A and 20A branch circuits, NEC Section
The maximum load that can be supplied by a 210.23(A)(2) allows fastened-in-place utilization
20A, three-wire, 120/240V circuit is: equipment to be connected in the same circuit
20A X 240V = 4,800VA with lighting units, cord- and plug-connected
utilization equipment not fastened in place, or
The maximum load that can be supplied by a
both. Under this condition, the fastened-in-place
20A, 208V, three-phase circuit is determined by
utilization equipment shall not exceed 50% of the
multiplying 20A by 208V by the square root of 3:
branch circuit ampere rating.
20A X 208V x V3 = Example 1:
A store has fluorescent lighting fixtures con­
20A X 208V X 1.732 = 7,205.12VA
sisting of nine fluorescent ballasts rated at 1.5A at
120V. The fixtures will operate continuously dur­
Lli The square root of 3 (written as V3) is ing normal business hours from 9:00 AM until
h-
O approximately 1.732. You may wish to make a 9:00 PM daily. What is the minimum size circuit
z
note of this for use in future calculations. breaker required for a branch circuit to serve this
load?
2 NCCER - Electrical LevelThree 26301-17
shall not exceed 80% of the branch circuit ampere
rating for 15A, 20A, and 30A circuits. Because the
Think About It
load is greater than 15A, determine the current-
Unit Load per Square carrying capacity of a 20A (the smallest logical
Foot size) circuit to serve this equipment:
20A X 0.8 = 16A
Referring to NEC Table 220.12, what is the unit
load per square foot for an office building where A 20A circuit is not sufficient; determine the
the actual number of general-purpose receptacle current-carrying capacity of a 30A circuit:
outlets is unknown?
30A X 0.8 = 24A
The minimum size branch circuit required is
Solution:
30A. Note that this solution assumes that only
Determine the branch circuit load:
multi-receptacle 20A and 30A branch circuits ex­
9 X 1.5A = 13.5A ist in the office. An alternate solution would be
to install a 20A individual branch circuit exclu­
Determine the continuous duty load (this is
sively for the copy machine.
a continuous duty load because the lighting fix­
Example 5:
tures will stay on for more than three hours):
What is the maximum lighting load that may
13.5A X 1.25 = 16.88A be connected to a 20A branch circuit supplying a
The minimum size circuit breaker required is piece of fixed equipment that has a rating of 8.5A,
20 A. 120V?
Example 2: Solution:
What is the maximum continuous load that The equipment rating is smaller than 50% of
may be connected to a 30A, 120V fuse? the rating of the 20A branch circuit. Therefore,
Solution: 11.5A of noncontinuous lighting may be added.
Per NEC Section 210.20(A):
20A - 8.5A = 11.5A
30A x (the reciprocal of 1.25) = Example 6:
30A x 1/125 = A restaurant dishwasher has a nameplate rat­
30A X 0.8 = 24A ing of 14.7A, 208V, 30. During busy times in the
restaurant, it is anticipated that the dishwasher
The maximum continuous load cannot exceed
will be turned on and operated for more than
24 A.
three hours at a time. What is the minimum size
Example 3:
branch circuit required to supply this equipment?
How many receptacle outlet devices in other-
than-residential occupancies can be connected Solution:
to a 20A, two-wire, 120V circuit? (The receptacle This equipment is considered a continu­
outlets serve noncontinuous duty loads.) ous load (operated for more than three hours).
Solution: Therefore, the load is to be multiplied by 125% to
Determine branch circuit capacity: determine the branch circuit size.
20A X 120V = 2,400VA 14.7A X 1.25 = 18.38A
The minimum size branch circuit required is
Per NEC Section 220.14(1), each outlet is assigned
20 A.
a load of 180VA, so:
2,400VA - 180VA = 13.33
1.2.0 Derating Factors
Thirteen receptacle outlets can be connected to
this circuit. The ampacity (current-carrying capacity) of
Example 4: branch circuit conductors must be derated when
An office manager has purchased a new state- any of the following circumstances apply:
of-the-art copy machine. The nameplate rating on
• There are more than three current-carrying
the copy machine is 17A, 120V. What is the mini­
conductors in a raceway per NEC Section
mum size branch circuit required to serve this
310.15(B)(3)(a).
equipment?
• The ambient temperature that the conductors
Solution: will pass through exceeds the temperature
This is not a continuous load; however, per ratings for conductors listed in NEC Table
NEC Sections 210.23(A)(1) and (B), the rating of 310.15(B)(2)(a) or NEC Table 310.15(B)(2)(b).
any one cord-connected utilization equipment
26301-17 Load Calculations - Branch and Feeder Circuits Module One 3