General Installation Requirements, Part XXV

Figure 1

In the 2017 National Electrical code (NEC), there are a few changes in 110.26. The first change is in subsection (A), which is part of a global change for the upper voltage threshold. When the 2011 edition of the Code was revised for 2014, the voltage threshold was changed from 600 volts (V) to 1,000V in many locations throughout the Code. In the 2017 edition, many more locations throughout the Code were changed from 600V to 1,000V.


The first change in Article 110 is the title of Part II in 2017, “1000 Volts, Nominal, or Less.” In the last edition, it was “600 Volts, Nominal, or Less.” 


That increased voltage threshold number first appears in 110.26(A), which states working space for equipment operating at 1,000V, nominal or less to ground and likely to require examination, adjustment, servicing or maintenance while energized shall comply with the dimensions of 110.26(A)(1), (A)(2), (A)(3) and (A)(4) or as required or permitted elsewhere.


An informational note has been added under 110.26(A), which states NFPA 70E 2015, Standard for Electrical Safety in the Workplace, provides guidance, such as determining severity of potential exposure, planning safe work practices, arc flash labeling and selecting personal protective equipment. As with all informational notes, it is informational only and is not enforceable as an NEC requirement.


Two new subsections under 110.26(A) have been added for working space requirements. Requirements in this new subsection have been added to ensure there will be enough working space in front of and around electrical equipment installed in spaces with limited access. The first new subsection is titled “Limited Access.”


A similar requirement was new in the 2014 edition, but it only pertained to electrical enclosures for resistance heating element-type duct heaters that are mounted on duct systems. This new working space requirement pertains to equipment operating at 1,000V, nominal or less to ground, that is likely to require examination, adjustment, servicing or maintenance while energized and required by installation instructions or function to be located in a space with limited access. For this type of equipment, all of the provisions in 110.26(A)(4)(a) through (d) apply.


The first provision states, where equipment is installed above a lay-in ceiling, there has to be an opening that is at least 22 inches by 22 inches. This first part does not specify the width or depth of the working space, just the opening to be able to get to the equipment.


For example, a 208V heating, ventilating and air conditioning (HVAC) unit is installed above a 2-foot-by-2-foot lay-in ceiling. Inside this unit, behind the access door, is equipment likely to require examination, adjustment, service or maintenance while energized. There is a full-size, 2-foot-by-2-foot ceiling tile located below and in front of the access door. The opening for a full-size 2-foot-by-2-foot ceiling tile is at least 22 inches by 22 inches. Therefore, the opening to be able to examine, adjust, service or maintain this HVAC unit while it is energized meets the stipulation in 110.26(A)(4)(a) (see Figure 1).


The provision in 110.26(A)(4)(a) also states, where equipment is installed in a crawl space, there has to be an accessible opening that is at least 22 inches by 30 inches. Like equipment above a lay-in ceiling, this provision does not specify the width and depth of the working space; it specifies the opening to be able to get to the equipment in a crawl space.


The next requirement in this section applies to working-space width for the equipment. The width of the working space shall be the width of the equipment enclosure or a minimum of 30 inches, whichever is greater [110.26(A)(4)(b)]. This width is not the total width of the equipment, such as an HVAC unit. It is the width of the enclosure housing the electrical components.


For example, an HVAC unit has been installed in a crawl space. The unit contains equipment that is likely to require examination, adjustment, service or maintenance while energized. The access door for entering and exiting the crawl space is 24 inches by 32 inches. The access door to the electrical components in the HVAC unit is 16 inches wide. One of this HVAC unit’s ducts is directly to the right of the access door, but there is no obstruction to the left.


Since the width of the equipment enclosure is less than 30 inches, the minimum width in front of the equipment enclosure is 30 inches. Because of the size of the access door to the crawl space, this installation meets the stipulation in 110.26(A)(4)(a). This installation also meets the requirement in 110.26(A)(4)(b) because there are at least 30 inches of working space width (see Figure 2).


Where equipment, located in a space with limited access, has hinged doors or panels, the doors or panels must be able to open a minimum of 90 degrees [110.26(A)(4)(c)]. This requirement is just like the requirement in 110.26(A)(2), which states, in all cases, the work space shall permit at least a 90-degree opening of equipment doors or hinged panels.


Depth and height requirements for equipment located in a space with limited access is in 110.26(A)(4)(d). The space in front of the enclosure shall comply with the depth requirements of Table 110.26(A)(1). The minimum depth of working space depends on the nominal voltage to ground and one of the three conditions. The three conditions are described under Table 110.26(A)(1). 


A height requirement is in the same subsection with the depth requirement, but it is different from the height requirement in 110.26(A)(3). In accordance with 110.26(A)(4)(d), the maximum height of the working space shall be the height necessary to install the equipment in the limited space. The minimum height of working space required by 110.26(A)(3) is 61/2 feet. There is no specific minimum dimension for working space height in 110.26(A)(4)(d); the minimum height is only the height necessary to install the equipment in the limited space. The last sentence in this subsection states a horizontal ceiling structural member or access panel shall be permitted in this space. This is an important clarification because, when electrical equipment is located above a lay-in ceiling, a person working on the equipment is usually on a ladder or a lift.


For example, a 208V HVAC unit is installed above a 2-foot-by-2-foot lay-in ceiling. In front of and below the access door to the HVAC unit is a full-size 2-foot-by-2-foot ceiling tile. The working space in front of the access door to the HVAC unit is at least 3 feet, which complies with the minimum required dimension specified in Table 110.26(A)(1). The working space height in front of the access door for this HVAC unit is enough height to install the equipment. Because the working space requirements for this HVAC unit meets the requirements in 110.26(A)(4), this installation is permitted (see Figure 3).


Since the requirement in 110.26(A)(4) pertains to all equipment installed above a lay-in ceiling operating at 1,000V, nominal or less to ground and likely to require examination, adjustment, service or maintenance while energized, the specific requirement for electrical enclosures for resistance heating element-type duct heaters that are mounted on duct systems is no longer needed. Therefore, 424.66(B) has been deleted.


The second new subsection under 110.26(A) requires the high-voltage equipment to be separated from the space occupied by the low-voltage equipment by a suitable partition, fence or screen [110.26(A)(5)]. This applies where switches, cutouts or other equipment operating at 1,000V, nominal or less are installed in a vault, room or enclosure where there are exposed live parts or exposed wiring operating over 1,000V, nominal. 


Unlike other requirements in 110.26 that specify certain minimum dimensions, this requirement does not. Where electrical equipment operating at 1,000V, nominal or less is in the same vault, room or enclosure as equipment with exposed live parts or exposed wiring operating over 1,000V, nominal, the two types of equipment shall be effectively separated from each other. In this type of installation, it is not enough for the separation to be by a certain distance only. The high-voltage equipment shall be effectively separated by a suitable partition, fence or screen from the space occupied by the low-voltage equipment.


This requirement does not apply to high-voltage equipment with no exposed live parts or exposed wiring. It only applies to electrical equipment where there are exposed live parts or exposed wiring operating over 1,000V, nominal.


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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