Without very specific National Electrical code (NEC) rules for determining the right size conductor and the correct size overcurrent protective device, a conductor could overheat and even start a fire. Rules for access and working space are in place to ensure electrical equipment can be operated and maintained in a safe manner.

For electrical equipment operating at 600 volts (V), nominal, or less, access and working space requirements are in 110.26. This section’s first subsection contains working space depth, width and height requirements. The second subsection states working space required by 110.26 shall not be used for storage.

Section 110.26(C) pertains to working space entrances and exits. The first subsection requires at least one entrance of sufficient area to be provided to give access to and egress from working space around electrical equipment. For large equipment rated 1,200 amperes (A) or more and more than 6 feet wide containing overcurrent devices, switching devices or control devices, each end of the working space shall have an entrance to and egress from the required working space. If energized parts are exposed and there is an incident, such as an arc flash, workers need a safe way to escape.

Where a space contains large equipment, a single entrance to and egress from the required working space is permitted if the installation complies with 110.26(C)(2)(a) or (b). Where the location for large equipment permits a continuous, unobstructed way of egress travel, a single entrance to the working space is permitted. With this, there must be an unobstructed way of egress travel at each end as well as at all points in between.

For example, a 1,200A, three-phase, 480Y/277V switchboard will be installed in an electrical room with concrete block walls. The width of the switchboard is 6 feet, 8 inches. There will only be one door into and out of this room, directly across from the center of the switchboard. 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 as well as at all points in between. If there is an incident with the switchboard and someone is trying to exit the room from anywhere in the working space, there will be a direct way out of the room. In accordance with 110.26(C)(2)(a), having only one door is permitted because there is a continuous and unobstructed way of egress travel from the working space (see Figure 1).

The second option for having only one entrance to and egress from the required working space pertains to the working space depth. Where depth is twice that required by 110.26(A)(1), a single entrance shall be permitted, per 110.26(C)(2)(b). The working space depth or minimum clear distance in front of the electrical equipment is in Table 110.26(A)(1). The depth is dependent on the nominal voltage to ground and what is on the other side of the working space. To comply with the first part of 110.26(C)(2)(b), the minimum clear distance in front of the electrical equipment has to be at least twice the distance required by Table 110.26(A)(1).

To have a single entrance, there is another requirement. It shall be located so the distance from the equipment to the nearest entrance edge is not less than the minimum clear distance specified in Table 110.26(A)(1) for equipment operating at that voltage and in that condition, per 110.26(C)(2)(b). The distance between the equipment and the door only has to be the distance shown in Table 110.26(A)(1), not twice that distance.

For example, an 8-foot-wide, 2,000A, three-phase, 480Y/277V switchboard will be installed in an electrical room. On the other side of the working space is a concrete block wall. There will only be one door, located on the side wall. Since there will be only one entrance, the working space has to be double the distance shown in Table 110.26(A)(1).

Because the voltage to ground is 277V, the minimum distance will be one of the distances shown on the bottom row. A concrete block wall is considered as grounded, so this switchboard will be Condition 2. The minimum clear distance for this switchboard to the concrete block wall is 3 feet, 6 inches. This means there has to be at least 7 feet (3.5 × 2 = 7) of clear distance in front of this switchboard. Also, to have one entrance, the distance from the closest switchboard edge to the entrance has to be at least 3 feet, 6 inches (see Figure 2).

Unless the electrical equipment is large, there is no minimum distance required from the electrical equipment to the entrance. For example, a 2,000A, three-phase, 480Y/277V switchboard with a width of 8 feet will be installed in an electrical room. On the other side of the working space will be three 400A, 208Y/120V panelboards. None of these panelboards will be wider than 6 feet. Since there will only be one door into and out of this room—located on the side wall—the working space has to be double the distance shown in Table 110.26(A)(1).

Because the voltage to ground is 277V, the minimum distance will be one of the distances shown on the bottom row. Because of exposed live parts on both sides of the working space, this switchboard will be Condition 3. The minimum clear distance to the panelboards is 4 feet. This means there has to be at least 8 feet (4 × 2 = 8) of clear distance in front of this switchboard. To have one entrance, the distance from the closest switchboard edge to the entrance has to be at least 4 feet. The panelboards are not considered large, so no requirement prevents them from being installed close to the entrance (see Figure 3).

The next section in 110.26(C) was added to the NEC in 2008. For the last two editions, this provision was for equipment rated 1,200A or more, but this changed in 2014. Now, this provision pertains to equipment rated 800A or more. Where equipment rated 800A or more that contains overcurrent devices, switching devices or control devices is installed and there is a personnel door intended for entrance to and egress from the working space less than 25 feet from the nearest working space edge, the door(s) shall open in the direction of egress and be equipped with listed panic hardware, per 110.26(C)(3).

The last part of the sentence was also simplified. Instead of this section requiring doors to be equipped with panic bars, pressure plates or other devices that are normally latched but open under simple pressure, the doors are now required to be equipped with listed panic hardware (see Figure 4).

Note that this section does not state listed panic hardware is required on only one set of doors. In accordance with 110.26(C)(3), any and all personnel doors less than 25 feet from the nearest working space edge 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, an 800A, three-phase, 480Y/277V switchboard will be installed in an electrical room. There is only one entrance/exit door for this electrical room, and it 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 800A switchboard. 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 working space edge 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 be equipped with listed panic hardware (see Figure 5).

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