Thousands of public inputs (formerly proposals) are usually submitted for revising the next edition of the National Electrical Code (NEC). With some editions, there are global, Code-wide changes. One of the Code-wide changes in the 2014 edition was raising the voltage threshold from 600 to 1,000 volts (V) in a number of locations.


In the 2014 edition, one article where the voltage threshold did not change was Article 110. Part II contained provisions for electrical systems and equipment rated 600V, nominal, or less. Part III contained provisions for electrical systems and equipment rated over 600V, nominal. 


In the 2017 edition, the voltage threshold was raised from 600 to 1,000V in more locations throughout the NEC. Part II in Article 110 contains provisions for electrical systems and equipment rated 1,000V, nominal, or less. Part III contains provisions for electrical systems rated over 1,000V, 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. Requirements in 110.33 are similar to those in 110.26(C) for equipment rated 1,000V, nominal, or less. The basic rule for equipment rated 1,000V, nominal, or less states at least one entrance of sufficient area shall be provided to give access to and egress from working space about electrical equipment.


With equipment under the provisions of 110.26(C), there is no minimum width or height for the entrance unless the equipment is rated 1,200 amperes (A) or more and wider than 6 feet. With equipment under the provisions of 110.33(A), there is minimum width and height for the entrance regardless of the width and rated amperes of the equipment. At least one entrance to enclosures for electrical installations as described in 110.31 not less than 24 inches wide and 6 feet, 6 inches high shall be provided to give access to the working space about electrical equipment [110.33(A)]. This is the minimum size opening into and out of the working space; the actual opening can be larger. For example, one of the entrances into an electrical room is through a door that can be locked to keep out unqualified people. The size of this door is 40 inches wide by 6 feet, 8 inches high (see Figure 1).


Section 110.33(A) pertains to large equipment. The term “large equipment” is mentioned only three times in the NEC: 110.26(C)(2), 110.33(A)(1) and 314.24(B)(1). The first sentence under 110.33(A)(1) requires one entrance at each end of large equipment (switchgear and control panels) when the equipment is wider than 6 feet. The specification for large equipment rated over 1,000V, nominal, is not the same as the specification for large equipment rated 1,000V, nominal, or less. For equipment rated 1,000V, nominal, or less, large equipment is equipment over 6 feet wide and rated 1,200A or more [110.26(C)(2)]. For equipment rated over 1,000V, nominal, the ampacity of the equipment is not a factor in determining if the equipment is large or not. Unless meeting one of the considerations in 110.33(A)(1)(a) or (A)(1)(b), one entrance at each end of the equipment shall be required when the equipment is rated over 1,000V, nominal.


For example, a 1,000A, 3-phase, 4,160Y/2,400V switchgear will be installed in an electrical room of an industrial facility. The switchgear is 6 feet, 2 inches wide. A 1,000A, 3-phase, 480Y/277V switchboard will be installed directly across from the switchgear. The distance between the switchgear and the switchboard will be 5 feet. This switchgear is considered large equipment because the width exceeds 6 feet. This switchboard is not considered large equipment because it is not rated 1,200A or more. Because of the switchgear, one entrance at each end of the equipment (or the working space) is required (see Figure 2).


With large equipment rated over 1,000V, nominal, a single entrance to the required working space shall be permitted where either of the conditions in 110.33(A)(1)(a) or (A)(1)(b) is met. Where the location for large equipment permits a continuous and unobstructed way of exit travel, a single entrance to the working space shall be permitted [110.33(A)(1)(a)]. With this option, there has to be unobstructed egress travel at each end as well as all points between.


For example, a 2,000A, 3-phase, 4,160Y/2,400V switchgear will be installed in an electrical room with concrete block walls. The switchgear is 6 feet, 8 inches wide. There will only be one door into and out of this electrical room located directly across from the center of the switchgear. The distance to the concrete block wall (and the door) in front of the switchgear is 4 feet. The size of this door will be 3 feet wide by 6 feet, 8 inches high. Listed panic hardware will be installed on this door. In this installation, there will be an unobstructed way out of the room from each end of the switchgear as well as all points between. If there is an electrical incident with this switchgear and someone is trying to exit the room from any point in front of the switchgear, there will be a direct (unobstructed) way out of the room. In accordance with 110.33(A)(1)(a), having only one door is permitted because there is a continuous and unobstructed way of egress travel from this switchgear’s working space (see Figure 3).


The second option for having only one entrance to and egress from the required working space is dependent on the depth of the working space and the distance from the equipment to the nearest edge of the entrance. Where the depth of the working space is twice that required by 110.34(A), a single entrance shall be permitted [110.33(A)(1)(b)]. For equipment rated over 1,000V, nominal, the depth of working space or minimum clear distance in front of the electrical equipment is in Table 110.34(A). The depth is dependent on nominal voltage to ground and what is on the other side of the working space.


To comply with the first part of 110.33(A)(1)(b), the minimum clear distance in front of the electrical equipment has to be at least twice the distance required by Table 110.34(A). To have a single entrance, there is another requirement in this section. It shall be located so that the distance from the equipment to the nearest edge of the entrance is not less than the minimum clear distance specified in Table 110.34(A) for equipment operating at that voltage and in that condition [110.33(A)(1)(b)]. The distance between the equipment and the door only has to be the distance shown in Table 110.34(A), not twice that distance.


For example, a 2,000A, 3-phase, 4,160Y/2,400V switchgear will be installed in an electrical room. The switchgear is 8 feet wide. Across from the switchgear will be a concrete block wall. There will only be one door into and out of this electrical room, and it will be located on the side wall. Since there will be only one entrance, the working space has to be double the distance shown in Table 110.34(A). Because the voltage to ground is 2,400V, the minimum clear distance will be one of the distances shown in the top row.


The three conditions are explained below the table. Condition 1 is where there are exposed live parts on one side of the working space and no live or grounded parts on the other side of the working space. Condition 1 also is where there are exposed live parts on both sides of the working space but they are effectively guarded by insulating materials. Condition 2 is where there are exposed live parts on one side of the working space and grounded parts on the other side. The next sentence under Condition 2 helps by showing a few things that are considered grounded. Concrete, brick, and tile walls shall be considered grounded. Condition 3 is where there are exposed live parts on both sides of the working space. A concrete block wall is considered as grounded so the minimum clear distance for this switchgear will be under Condition 2. The minimum clear distance for this switchgear to the concrete block wall is 4 feet. This means there has to be at least 8 feet (4 × 2 = 8) of clear distance in front of this switchboard. Also, for this electrical room to have only one entrance, the distance from the closest edge of this switchgear to the nearest edge of the entrance shall be at least 4 feet (see Figure 4).


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