General Installation Requirements, Part XXXIV

Figure 1

National Electrical Code (NEC) sections 90.5(A) and (B) explain how to recognize mandatory rules and permissive rules. In accordance with 90.5(A), mandatory rules identify actions that are specifically required or are specifically prohibited. Mandatory rules are easy to recognize because the terms “shall” or “shall not” are used. In the Code, the term “shall” is used more than 12,000 times, and the term “shall not” is used almost 1,900 times.


An example of a section containing a mandatory rule by using the term “shall” is 110.3(B): “Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.” Sections 110.3(B) and 110.26(A)(1) contain a mandatory rule by using the term “shall not”: “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) unless the requirements of 110.26(A)(1)(a), (A)(1)(b), or (A)(1)(c) are met.”


In accordance with 90.5(B), permissive rules identify actions that are allowed but not required. Permissive rules are also used to describe options or alternative methods. The terms “shall be permitted” or “shall not be required” are used in permissive rules. In the Code, the term “shall be permitted” is used more than 2,400 times, and the term “shall not be required” is used more than 400 times. An example of a section containing a permissive rule by using the term “shall be permitted” is 110.14(C): “­Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction or both.” An example of a section containing a permissive rule by using the term “shall not be required” is 110.26(A)(1)(a): “Working space shall not be required in the back or sides of assemblies, such as dead-front switchboards, switchgear or motor control centers, where all connections and all renewable or adjustable parts, such as fuses or switches, are accessible from locations other than the back or sides.” 


Part III in Article 110 contains provisions for electrical systems rated over 1,000 volts (V), nominal. Part III includes 110.30 through 110.41. Requirements for entrances to enclosures, and access to working space for electrical systems rated over 1,000V, nominal, are in 110.33. As stated in 110.33(A)(2), where bare energized parts at any voltage or insulated energized parts above 1,000V, nominal, are located adjacent to such entrance, they shall be suitably guarded. In accordance with the definition in Article 100, “guarded” means covered, shielded, fenced, enclosed or otherwise protected by means of suitable covers, casings, barriers, rails, screens, mats or platforms to remove the likelihood of approach or contact by people or objects to a point of danger. 


The next section in 110.33(A) pertains to personnel doors. Where there are personnel doors intended for entrance to and egress from the working space less than 25 feet from the nearest edge of the working space, the doors shall open in the direction of egress and be equipped with listed panic hardware [110.33(A)(3)]. Part II of Article 110 contains a similar requirement and applies to electrical equipment rated 1,000V, nominal, or less. Both sections state all personnel doors intended for entrance to and egress from the working space less than 25 feet from the nearest edge of the working space shall open in the direction of egress and be equipped with listed panic hardware. 


The requirements in 110.26(C)(3) apply to equipment that contains overcurrent devices, switching devices or control devices when there is equipment rated 800 amperes (A) or more. The requirements in 110.26(C)(3) do not apply to equipment rated less than 800A.


The requirement in 110.33(A)(3) is not dependent on an equipment ampere rating. For example, an electrical room contains electrical equipment rated 600A and over 1,000V, nominal. There are two personnel doors intended for entrance to and egress from the electrical equipment in this room. Both doors are located less than 25 feet from the nearest edge of the working space, and both doors open in the direction of egress. Both doors are also equipped with listed panic hardware (see Figure 1).


This section does not state that listed panic hardware is required only on the doors going into the room where the equipment is located. In accordance with 110.33(A)(3), all personnel doors that are less than 25 feet from the nearest edge of the working space shall open in the direction of egress and be equipped with listed panic hardware if those doors are intended for entrance to and egress from the working space.


For example, a 1,000A, three-phase, 4,160Y/2,400V switchgear will be installed in an electrical room. There is only one entrance/exit door for this electrical room. The electrical room door opens into a hallway. There are two doors in this hallway, and both doors are intended for entrance to and egress from the electrical room. Both doors are less than 25 feet from the working space of the 1,000A switchgear. The electrical room door shall open in the direction of egress and be equipped with listed panic hardware. Since both hallway doors are less than 25 feet from the nearest edge of the working space and both are intended for entrance to and egress from the electrical room, both hallway doors shall open in the direction of egress from the electrical room, and both shall be equipped with listed panic hardware (see Figure 2).


Where electrical equipment rated over 1,000V, nominal, is installed on platforms, balconies or mezzanine floors, or in attic or roof rooms or spaces, permanent ladders or stairways shall be provided for safe access to the working space around the electrical equipment [110.33(B)]. While providing safe access to the working space around electrical equipment is always a great idea, there is no requirement to provide permanent ladders or stairways where electrical equipment rated 1,000V, nominal, or less, is installed on platforms, balconies, or mezzanine floors or in attic or roof rooms or spaces.


Working space provisions for electrical equipment rated over 1,000V, nominal, is in 110.34(A). Except as elsewhere required or permitted in the Code, equipment likely to require examination, adjustment, servicing or maintenance while energized shall have clear working space in the direction of access to live parts of the electrical equipment and shall be not less than specified in Table 110.34(A). 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 it will be examined while energized, the working space shall not be less than specified in Table 110.34(A). Knowing how to measure the distance is just as important as knowing the distance itself. The second sentence in this section provides clarity on how distances are to be measured. Distances shall be measured from the live parts, if exposed, or from the enclosure front or opening, if enclosed.


For electrical equipment such as metal-enclosed switchgear, the distance shall be measured from the front of the equipment because the live parts are enclosed. Table 110.34(A) specifies minimum clear distances for depth of working spaces. This table is divided into five rows. The top row distances are used when the electrical equipment has a nominal voltage of 1,001–2,500V to ground. This table also includes four columns. The first column shows the five electrical systems. The next three columns are the three conditions for the electrical equipment. The conditions are explained below Table 110.34(A). All of the 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, but the distances are to be measured from the front of the equipment.


The first condition under Table 110.34(A) is 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 they are effectively guarded by insulating materials, this first condition would also apply. The minimum depth of clear working space at electrical equipment for systems rated between 1,001–2,500 nominal voltage to ground is 3 feet.


For example, 4,160Y/2,400V, three-phase, 4-wire switchgear will be installed in an electrical room. The wall across the aisle from the switchgear will be covered in a material that is not considered as grounded. Because of this, condition 1 applies. At first, it might seem like the minimum clear distance would be from the second row, which is 4 feet, but voltages shown are voltage to ground. In a 4,160Y/2,400V, three-phase, 4-wire system, 2,400V is the voltage to ground. The minimum depth of working space for the switchgear in this installation is 3 feet (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 classes and seminars on the electrical industry. He is the author of “Illustrated Guide to the National Electrical Code” and NFPA’s “Electrical Reference.” He can be reached at 615...

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