General Installation Requirements, Part XXXVII: Article 110

The scope in article 110 of the National Electrical Code (NEC) states the 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. Instead of the scope in Article 90 stating what Article 90 covers, it states what the entire NEC covers.

As stated in 90.2(A), the Code covers the installation and removal of electrical conductors, equipment and raceways; signaling and communications conductors, equipment and raceways; and optical fiber cables and raceways for the locations listed in 90.2(A)(1) through (A)(4). The first locations listed where NEC requirements apply are public and private premises, including buildings, structures, mobile homes, recreational vehicles and floating buildings. The second type of location includes yards, lots, parking lots, carnivals, and industrial substations. Out of the four groups listed in 90.2(A)(1) through (A)(4), the third group does not stipulate specific locations but types of installations. Installations of conductors and equipment that connect to the supply of electricity must be installed in accordance with NEC requirements.

The last locations listed where NEC requirements apply are installations used by the electric utility, such as office buildings, warehouses, garages, machine shops and recreational buildings that are not an integral part of a generating plant, substation or control center. A list of installations that are not compelled to comply with NEC requirements are shown in 90.2(B).

Electrical systems connecting to the supply of electricity come in a wide variety of voltages. Electrical systems supplying most dwelling units are 120/240-volt (V), single-phase, 3-wire systems. Most electrical systems supplying power to industrial facilities are three-phase voltage systems, and some of the most common are 208Y/120V, three-phase and 480Y/277V, three-phase systems. Many electrical systems supplying public and private premises are rated over 1,000V. Article 490 covers the general requirements for equipment operating at more than 1,000V, nominal, but this is not the only place in the Code containing rules for systems rated more than 1,000V. Two more articles are dedicated to such systems: Article 280, Surge Arresters Over 1,000 Volts, and Article 399, Outdoor Overhead Conductors over 1,000 Volts.

There also are 12 articles that have parts within the articles that contain requirements for electrical systems over 1,000V. Article 110, Part III contains requirements for conductors and equipment used on circuits over 1,000V, nominal.

Requirements in Section 110.34, Work Space and Guarding, pertain to illumination around working space for equipment over 1,000V. Per 110.34(D), illumination shall be provided for all working spaces about electrical equipment. This illumination requirement is the same for equipment over 1,000V as it is for equipment 1,000V or less. This section continues by saying the illumination shall not be controlled by automatic means only. This means that some type of automatic means of control can be installed, but there also needs to be a means to override it.

For example, an electrical room contains 2,000 ampere (A), three-phase, 4,160Y/2,400V switchgear. This electrical room has a single entrance to the working space which is permitted because there is a continuous and unobstructed way of exit travel. Next to the door, inside this electrical room, is an occupancy sensor switch that has a slide switch on the front with settings for off, auto and on. This automatic means of control is permitted because the slide switch on the front overrides the motion sensor (see Figure 1).

The requirement in 110.34(D), which says the illumination control shall not be by automatic means only, also is in 110.26(D). Section 110.26(D) is in Part II of Article 110, which contains requirements for equipment rated 1,000V, nominal, or less. Without this provision, workers could be left in the dark while working on energized conductors and circuit parts.

For example, a qualified person is standing in front of energized electrical equipment with their back facing the switch. Because of the task being performed by the qualified person, there is little to no movement, especially from the person’s back. Without the provisions in 110.26(D) and 110.34(D), the person could suddenly be in the dark because the motion-sensor switch is not detecting movement and the lighting is turned off.

Although the next two sentences in 110.34(D) are in different paragraphs, the point of each provision is the same. The first pertains to lighting outlets. The outlets shall be arranged so that people changing lamps or making repairs on the lighting system are not endangered by live parts or other equipment.

The second sentence pertains to lighting controls (switches). The points of control shall be located so that people are not likely to come in contact with any live part or moving part of the equipment while turning on the lights. The point of both sentences is to keep people out of danger when turning on lights, changing lamps, and making repairs on the lighting system (see Figure 2).

The title of 110.34(E) is Elevation of Unguarded Live Parts. Unguarded live parts above working space shall be maintained at elevations not less than required by Table 110.34(E). Because this table is in Part III of Article 110, it starts with a nominal voltage between phases of 1,001V. The voltage systems in Table 110.34(E) are in three rows; 1,001–7,500V, 7,501–35,000V, and over 35 kilovolts (kV)—the same as 35,000V.

When the voltage between phases is over 35 kV, a calculation will be necessary. For example, switchgear with a nominal voltage between phases of 150 kV has been installed and will have unguarded live parts above the switchgear. What is the minimum working space elevation that shall be maintained above this switchgear?

As shown in Table 110.34(E), the minimum elevation above unguarded live parts for systems over 35 kV is 9 feet, 6 inches plus 0.37 inches per kV above 35 kV. Start by finding the amount of kV above 35 kV for this system. In this case, the amount of kV above 150 kV is 115 kV (150 – 35 = 115).
Next, multiply 115 kV by 0.37. The additional distance required is 42.55 inches (115 × 0.37 = 42.55). Now, convert 9 feet, 6 inches to total inches: this comes to 114 inches (9 ft. × 12 in. = 108 in. + 6 in. = 114). Next, add the two dimensions to find the minimum elevation. The dimension of 114 inches plus 42.55 inches is 156.55 inches. The minimum working space elevation above 150 kV switchgear with unguarded live parts is 13 feet, 1 inch (156.55 in. ÷ 12 in. = 13.05 ft. = 13 ft. 1 in.) (see Figure 3).

Next month’s column continues the discussion of electrical installation requirements.

About the Author

Charles R. Miller

Code Contributor

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.”...

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