General Installation Requirements, Part XVII

Figure 1

Article 110 in the National Electrical Code (NEC) contains general requirements for electrical installations. Some of the topics covered include examination and approval, installation and use, and access to and spaces about electrical conductors and equipment.


Article 110 is divided into five parts. The first contains general requirements for all voltages. Part II, starting with 110.26, contains requirements for systems and equipment rated 600 volts (V), nominal, or less. Part III contains requirements for conductors and equipment used on circuits over 600V, nominal. This part covers sections 110.30 through 110.40, which supplement or modify Part I. Part IV contains requirements for tunnel installations over 600V, nominal. Part V contains requirements for manholes and other electrical enclosures intended for personnel entry, pertaining to all voltages.


The first section in Part II, 110.26, contains many requirements and specifications, covering almost two pages. While 110.26 is only one section, it contains six subsections, (A) through (F), and some are divided into even more subsections. In accordance with the first sentence in 110.26, access and working space shall be provided and maintained about all electrical equipment to permit ready and safe operation and maintenance. Because of the word “about,” the phrase in the heading of this section (Spaces About Electrical Equipment) may seem a little odd. However, “about” is the best word to describe which spaces are covered. Some words sometimes used in place of “about” are “around,” “round,” “near” and “nearby.”


While this section covers certain conditions and even mentions specific types of electric equipment, it starts with all electrical equipment.


Looking at the first sentence of 110.26, access and working space is required for all electrical equipment, not only equipment that is likely to require examination, adjustment, service or maintenance while energized. The working space is not only required but also shall be maintained. It is essential that this working space permits ready and safe operation and maintenance of such equipment.


The general rule in 110.26 states all electrical equipment shall have working space and access to be able to operate and maintain the equipment. Starting with 110.26(A), a specific condition applies to electrical equipment operating at 600V, nominal, or less to ground. If the electrical equipment is likely to require examination, adjustment, service or maintenance while energized, the working space shall comply with the dimensions of 110.26(A)(1), (A)(2) and 
(A)(3) or as required or permitted elsewhere in the NEC. For the specific workspace to be required, it is not necessary for the electrical equipment to require all four conditions while energized; only one condition is necessary. For example, if the electrical equipment will never be adjusted, serviced or maintained while energized but will be examined, the working space shall comply with the dimensions of 110.26(A)(1) through (A)(3).


If the electrical equipment will likely need to be examined, adjusted, serviced or maintained while energized, workspace of certain minimum dimensions will be required. For example, a switchboard will supply power to a transformer, and the transformer will supply power to a main-breaker panelboard. All of this equipment will be installed on one wall in an electrical room. Because the switchboard and panelboard will likely need to be examined, adjusted, serviced or maintained while energized, the workspace is required to comply with the dimensions of 110.26(A)(1) through (A)(3).


Will the transformer likely need to be examined, adjusted, serviced or maintained while energized? If the answer is yes, it will also need the workspace specified in 110.26(A)(1) through (3). If the only time the front cover of the transformer will be off is when the transformer is deenergized, the workspace specified in 110.26(A)(1) through (3) is not required. Determining a transformer’s output voltage is vital, especially when installing the transformer, but the voltage could be measured in the panelboard supplied by the transformer. While specific minimum working-space dimensions may not be required, access and working space are (see Figure 1).


A disconnect or safety switch is another piece of electrical equipment that may or may not need the workspace specified in 110.26(A)(1) through (3). For example, a fused safety switch will be installed to supply power to an outside air conditioning unit. If it is unlikely the cover of the disconnect will be open at any time for examination, adjustment, servicing or maintenance while the disconnect is energized, specific minimum working-space dimensions are not required. Even if specific minimum working-space dimensions are not required, having suitable working space is always a good idea (see Figure 2).


For electrical equipment likely to require examination, adjustment, service or maintenance while energized, the working space shall not be less than the dimensions specified in 110.26(A)(1) through (A)(3). The types of working space mentioned in these three sections include depth, width and height.


As stated in the first sentence in 110.26(A)(1), the depth of the working space in the direction of live parts shall not be less than that specified in Table 110.26(A)(1). Knowing how to measure the distance is just as important as the knowing the distance itself.


The second sentence provides clarity on measuring distances. Distances shall be measured from the live parts when live parts are exposed. If the live parts are enclosed, the distances shall be measured from the front or opening of the enclosure. For example, for electrical equipment such as panelboards, switchboards, safety switches, switchgear and motor control centers, the distance shall be measured from the front of the equipment because the live parts are enclosed.


Table 110.26(A)(1), divided into two rows, specifies minimum clear distances for depth of working spaces. Top-row distances are used when the electrical equipment has a nominal voltage of 150 and less to ground. Some of the systems included in this row include a 120/240V, single-phase, 3-wire system; 208Y/120V, three-phase, 4-wire system; and 240/120V, three-phase, 
4-wire system.


This table also includes four columns. The first shows the two electrical systems. The next three are the conditions for the electrical equipment. The conditions are explained below Table 110.26(A)(1). All conditions start with the phrase “exposed live parts.” Electrical equipment, such as safety switches and panelboards, will have exposed live parts when doors are open or covers are removed. The distances are to be measured from the front of the equipment.


The first condition applies where there are no live or grounded parts across from the electrical equipment in which the depth of working space is being considered. If exposed live parts are on both sides of the working space but are effectively guarded by insulating materials, this first condition would also apply.


For example, a 208Y/120V, three-phase, 4-wire switchboard will be installed in an electrical room. The wall across the aisle from the switchboard will be covered in Sheetrock (drywall, plasterboard, wallboard, gypsum board). Since the Sheetrock is not considered grounded, the first condition applies. The minimum depth of working space for the switchboard in this installation is 3 feet (see Figure 3).


A question sometimes comes up about surfaces such as concrete blocks and concrete walls. The second sentence in condition 2 under Table 110.26(A)(1) provides helpful information for some wall surfaces. Concrete, brick or tile walls shall be considered grounded.


For example, a 208Y/120V, three-phase, 4-wire switchboard will be installed in an electrical room. The wall across the aisle from the switchboard will be a concrete-block wall. Because the wall is considered grounded, condition 2 applies. The minimum depth of working space for the switchboard is 3 feet (see Figure 4).


The third condition applies when there are exposed live parts on both sides of the working space. For example, a 208Y/120V, three-phase, 4-wire switchboard will be installed in an electrical room. Across the aisle from this switchboard will be an identical switchboard. Because live parts could be exposed in both switchboards at the same time, condition 3 applies. The minimum depth of working space for the switchboard in this installation is 3 feet (see Figure 5).


If the electrical equipment has a nominal system voltage to ground of 150V or less, it does not matter which condition applies because the minimum clear distance in front of the equipment is 3 feet.


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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