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General Installation Requirements

By Charles R. Miller | Feb 15, 2015
Figure 1

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There have been countless changes, both in the electrical industry and in the National Electrical Code (NEC), since the first edition in 1897. While a lot has changed, the reason and purpose of the Code have remained constant. As stated in 90.1(A), the purpose of the Code is the practical safeguarding of persons and property from hazards arising from electricity use. Protecting people and property from these hazards was the primary reason to create the first set of nationally adopted rules to govern electrical installations and operations. 


With each new edition of the Code come many changes, but the purpose has remained unchanged for a very long time. The purpose is stated in the first sentence, in the first section of the NEC, and the wording has remained exactly the same since the 1975 edition. In accordance with 90-1(a) of the 1971 edition, the purpose of this Code is the practical safeguarding of persons and buildings and their contents from hazards arising from the use of electricity for light, heat, power, radio, signaling and for other purposes. Because the second sentence in 90.1(A) of the 2014 edition is covered with gray shading, it looks like it has been revised or that it is new, but that is not the case. Until the 2014 edition, this sentence was in 90.1(C) under the subheading “intention.” Like the first sentence, this second sentence has also been in the Code for many years and many editions. In accordance with this sentence, the Code is not intended as a design specification or an instruction manual for untrained people.


The next section in Article 90 is scope, which shows what the Code covers and what it does not. The scope in every other article shows what that article covers. Except for Article 90 and 100, the scope of each article is located in its dot-one (.1) section (For example, the scope of Article 110 is located in 110.1). The scope of Article 100 does not have a section number because Article 100 is not numbered. 


Scopes are significant because they are like mini indexes to what the article covers. For example, as stated in 110.1, this article covers general requirements for the examination and approval, installation and use, access to and spaces about electrical conductors and equipment; enclosures intended for personnel entry; and tunnel installations. 


Article 110 is significant because it is in one of the four chapters that apply generally to all electrical installations. The next section after the scope of Article 110 pertains to the approval of conductors and equipment. The conductors and equipment required or permitted by this Code shall be acceptable only if approved [110.2]. As defined in Article 100, approved means acceptable to the authority having jurisdiction (AHJ). 


Also defined in Article 100, an AHJ is an organization, office or individual responsible for enforcing the requirements of a code or standard or for approving equipment, materials, an installation or a procedure. 


An informational note under 110.2 is helpful in fully understanding this section. It recommends looking at 90.7, Examination of Equipment for Safety and 110.3, Examination, Identification, Installation, and Use of Equipment. The informational note also recommends looking at the definitions of of the terms “identified,” “labeled” and “listed.” The definitions for these three terms are in Article 100. Identified (as applied to equipment) means recognizable as suitable for the specific purpose, function, use, environment, application, and so forth, where described in a particular Code requirement. Equipment and materials that are listed or labeled are acceptable to the AHJ and, therefore, are approved in accordance with 110.2. One organization that comes to mind when thinking of listing and labeling is Underwriters Laboratories Inc., but it is not the only organization capable of providing safety certification. Any organization that tests for safety and lists, labels or accepts equipment or materials, is a nationally recognized testing laboratory.


Section 110.3 is divided into two subsections. The first pertains to the equipment examination. In judging equipment, there are certain considerations; the list of items that shall be evaluated is in 110.3(A)(1) through (8). Some of the considerations include suitability of equipment; mechanical strength and durability; wire-bending and connections space; electrical insulation; heating effects under normal and abnormal conditions; arcing effects; classification by type, size, voltage, current capacity and specific use; and other factors that contribute to the practical safeguarding of people using or likely to come in contact with the equipment. 


Even for something basic, such as installing a panelboard and branch circuits, there are many considerations for selecting the appropriate equipment. For example, a panelboard will be installed in a commercial building and will be supplied by a feeder. This panelboard will supply a number of branch circuits. The feeder and branch circuits will be enclosed in electrical metallic tubing (EMT). Even with this installation, there is a lot of equipment that must be evaluated to make sure it complies with 110.3(A). 


“Equipment,” as defined in Article 100, is a general term, including fittings, devices, appliances, luminaires, apparatus, machinery and the like, used as a part of, or in connection with, an electrical installation. Besides the panelboard, itself, all of the equipment (circuit breakers, conductors, raceways, equipment grounding terminal bar, fittings, etc.) shall be evaluated with the considerations in 110.3(A) (see Figure 1).


The second subsection under 110.3 may be one of the most overlooked in the Code, because it contains the word “instructions.” Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling [110.3(B)]. 


This section basically means to read and follow the instructions. Some instructions simply say to install in accordance with NEC requirements. 


Other instructions provide specific guidelines. For example, a heating and air conditioning unit will be installed on the roof of a commercial building. The installation and service manual contains both general and specific guidelines. One of the general instructions states, “All field wiring must be done in accordance with National Electrical Code requirements.” One of the specific instructions states, “To avoid the risk of fire or equipment damage, use only copper conductors.” Normally, installing aluminum conductors is not a violation, but it would be in this example. Because the instructions say so, copper conductors must be installed to supply this heating and air conditioning unit (see Figure 2).


Section 110.4 states that, throughout the Code, the voltage considered shall be that at which the circuit operates. The voltage rating of electrical equipment shall not be less than the nominal voltage of a circuit to which it is connected. As defined in Article 100, nominal voltage is a nominal value assigned to a circuit or system for the purpose of conveniently designating its voltage class (e.g., 120/240 volts, 480Y/277V, 600V). In accordance with the first informational note under the definition, the actual voltage at which a circuit operates can vary from the nominal within a range that permits satisfactory operation of equipment. For example, a 10 horsepower, three-phase motor will be supplied from a three-phase, 208Y/120V system. This motor is designed to operate at a nominal voltage of either 208, 230 or 460V. Since this motor will be connected to a 208V supply, the actual voltage could be a little less or a little more than 208. Regardless, the nominal voltage is 208Y/120V (see Figure 3).


Next month’s column continues the discussion of Article 110.

About The Author

Charles R. Miller, owner of Lighthouse Educational Services, teaches custom-tailored seminars on the National Electrical Code and NFPA 70E. He is the author of “Illustrated Guide to the National Electrical Code” and “Electrician's Exam Prep Manual.” He can be reached at 615.333.3336 and [email protected]. Connect with him on LinkedIn.

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