One way to help safeguard people from hazards arising from electricity use is to ensure there is sufficient working space in front of and around electrical equipment. Article 110.26 in the National Electrical Code (NEC) contains specifications for the working space dimensions required around all electrical equipment. This working space also shall be maintained to permit ready and safe operation and maintenance of such equipment. The minimum dimensions for depth, width and height of working space are covered in 110.26(A)(1), (A)(2) and (A)(3).
The dimension for height of working space for equipment operating at 600 volts (V), nominal, or less to ground and likely to require examination, adjustment, servicing or maintenance while energized shall comply with the 110.26(A)(3). The work space shall be clear and extend from the grade, floor or platform to a height of 61/2 feet or the height of the equipment, whichever is greater. The electrical equipment itself may have a height that is less than 61/2 feet, but if it is mounted so the top of the equipment is higher than 61/2 feet, the minimum working space height shall be the equipment height.
For example, a panelboard is installed next to a disconnect (safety) switch on a concrete block wall. The actual panelboard height is 5 feet, 4 inches, but it is mounted 20 inches from the floor. The top of the panelboard is 84 inches (7 feet) above the floor. In this installation, no circuit breaker (in its highest position) is more than 6 feet, 7 inches above the floor. Therefore, this installation complies with 404.8(A). The top of the disconnect switch is only 72 inches (6 feet) above the floor. Since the top of the panelboard is more than 61/2 feet above the floor, the minimum working space height required for this panelboard is the height of the panelboard. The minimum working space height required for this disconnect switch is 61/2 feet (see Figure 1).
The second sentence in 110.26(A)(3) states that, within this section’s height requirements, other equipment located above or below the electrical equipment can extend beyond the front of the equipment, but the difference in depth shall not be more than 6 inches. It is important to note that the other equipment has to be associated with the electrical installation.
For example, two panelboards are mounted above a trough (wireway). Since the trough contains conductors for the panelboards, it is associated with the electrical installation. Each panelboard is 6 inches deep, and the depth of the trough is 12 inches. Since the depth difference is not more than 6 inches, this installation is permitted (see Figure 2).
There is no limit to the number of items permitted above or below the electrical equipment within the height requirements of 110.26(A)(3) as long as the other equipment is associated with the electrical installation and does not extend beyond the front of the equipment by more than 6 inches. Note that no requirement restricts the electrical equipment within the height requirements of 110.26(A)(3) from extending more than 6 inches beyond the front of other associated equipment unless the other equipment also requires working space.
For example, a trough is installed above a switchboard. It is associated with the electrical installation and, therefore, can be within the dedicated equipment space for the switchboard. The trough’s depth is 12 inches, and the switchboard’s depth is 24 inches. Although the switchboard extends more than 6 inches beyond the front of the trough, the installation is permitted (see Figure 3).
The actual depth of the electrical equipment and the associated equipment can have a difference of more than 6 inches, as long as the depth difference after installation is not more than 6 inches. For example, a 4-inch-deep panelboard needs to be installed above a 12-inch-deep trough. The trough contains conductors for the panelboard; therefore, it is associated with the electrical installation. If the panelboard were mounted directly to the wall above the trough, the installation would be in violation of 110.26(A)(3) because the trough would extend 8 inches beyond the front of the panelboard. The maximum distance it can extend beyond the panelboard is 6 inches. In this installation, 2-inch-square steel tubing will be mounted to the wall and the panelboard will be mounted to the tubing. After the panelboard is installed 2 inches off the wall, the depth difference is not more than 6 inches. Since the trough, after installation, does not extend more than 6 inches beyond the front of the panelboard, this installation is permitted (see Figure 4).
An old common practice was to install a transformer on the floor in front of a panelboard. In the 1996 NEC, a sentence was added in Section 110-16(a), pertaining to working clearances, and it permitted other equipment within the work space; however all of the equipment in the work space had to be of equal depth. Besides a number of revisions to this section in the 1999 edition, the section was renumbered from 110-16 to 110-26.
In the 1999 NEC, a new subsection covered working space height. The requirement was changed to permit other equipment associated with the electrical installation to be installed above or below the electrical equipment as long as it did not extend more than 6 inches beyond the front of the equipment. Although it was previously permitted, installing a transformer on the floor in front of a panelboard is no longer permitted unless the front of the transformer does not extend more than 6 inches in front of the panelboard (see Figure 5).
The working space height section contains two exceptions. The first pertains to existing dwelling units where service equipment or panelboards that do not exceed 200 amperes shall be permitted in spaces where the working space height is less than 61⁄2 feet [110.26(A)(3) Exception No. 1].
The second exception was new in the 2011 NEC. Meters installed in meter sockets shall be permitted to extend beyond the other equipment. This section states the meter socket shall be required to follow the rules of this section.
For example, a meter socket (meter base) has been installed over a weather-proof panelboard. The depth of the meter base and the outdoor panelboard are 4 inches. The utility company’s meter extends beyond the front of the meter base by 8 inches. Since the meter base and panelboard are the same depth, the utility company’s meter extends beyond the front of the panelboard by 8 inches. Without 110.26(A)(3) Exception No. 2, this installation would be a violation. However, since meters installed in meter sockets can extend more than 6 inches beyond the panelboard, this installation is permitted (see Figure 6).
Next month’s column continues the discussion of electrical installation requirements.