Article 110 in the National Electrical Code (NEC) contains general requirements for electrical installations. Topics include examination and approval, installation and use, and access to and spaces about electrical conductors and equipment. This article is divided into five parts.
Part I covers general requirements for all voltages and includes sections 110.1 through 110.25. The second part in this article contains requirements for systems and equipment rated 1,000 volts (V), nominal, or less. Part II starts with Section 110.26 and ends with 110.28. Part III contains requirements for conductors and equipment used on circuits over 1,000V, nominal. This part includes sections 110.30 through 110.41. Requirements in Part III supplement or modify requirements in Part I. Part IV contains requirements for tunnel installations over 1,000V, nominal. This part includes sections 110.51 through 110.59. Part V contains requirements for manholes and other electrical enclosures intended for personnel entry, pertaining to all voltages. This part includes sections 110.70 through 110.79.
Section 110.26 states that access and working space shall be provided and maintained about all electrical equipment to permit ready and safe operation and maintenance of the equipment. This first provision is general and does not say how much space must be around electrical equipment. It does not even specify the equipment. The first subsection under 110.26 provides specific working space dimensions for equipment operating at 1,000V, nominal, or less to ground and likely to require examination, adjustment, servicing or maintenance while energized [110.26(A)].
This section later mentions equipment space again but not work space. The equipment space mentioned in 110.26(E) pertains to specific electrical equipment. All switchboards, switchgear, panelboards and motor control centers shall be located in dedicated spaces and protected from damage. Dedicated equipment space is not required for all types of electrical equipment, just those mentioned above. While there is nothing wrong with having dedicated space for equipment such as safety switches (disconnects), motor controllers (starters), meter socket enclosures, and transformers, it is not required (see Figure 1).
The section “Dedicated Equipment Space” is divided into two subsections. The first pertains to indoor installations. Switchboards, switchgear, panelboards and motor control centers installed indoors shall comply with 110.26(E)(1)(a) through (E)(1)(d). The first section for indoor installations shows the required dedicated space. The space equal to the width and depth of the equipment and extending from the floor to a height of 6 feet above the equipment or to the structural ceiling, whichever is lower, shall be dedicated to the electrical installation [110.26(E)(1)(a)]. This dedicated space—sometimes referred to as the footprint of the equipment—is required for switchboards, switchgear, panelboards and motor control centers.
For equipment mounted on the floor, such as most switchboards, switchgear and motor control centers, dedicated space is only required above the equipment. Panelboards are not normally mounted on the floor, so the space equal to the width and depth of the equipment above and below the equipment shall be dedicated to the electrical installation.
For example, a switchboard, low-voltage switchgear, a panelboard and a motor control center have been installed in an electrical room in an industrial plant. The structural ceiling is about 15 feet higher than the top of the tallest piece of equipment. Because the structural ceiling is more than 6 feet above the top of the tallest piece of equipment, the required dedicated space shall extend to 6 feet above the top of each piece of equipment. Because the panelboard is the only piece of equipment not mounted on the floor, dedicated equipment space is required from the bottom of the panelboard to the floor (see Figure 2).
Systems foreign to the electrical installation are not permitted below the electrical equipment. Where the structural ceiling is within 6 feet of the top of the equipment, systems foreign to the electrical installation are not permitted above the equipment. The last sentence in 110.26(E)(1)(a) provides additional clarity by stating no piping, ducts, leak protection apparatus or other equipment foreign to the electrical installation shall be located in this zone.
For example, a panelboard has been mounted on a concrete block wall. The structural ceiling is 6 feet above the top of the panelboard. An HVAC duct has been installed against the structural ceiling, but it is located directly above the panelboard. A plumbing pipe has been installed below the panelboard. There is a violation of 110.26(E)(1)(a) because the plumbing pipe is located below the panelboard within the dedicated equipment space. There is another violation of this same section because the HVAC duct is within the footprint of the panelboard and not more than 6 feet above the top of the panelboard (see Figure 3).
Depending on the condition, the depth of working space as required by 110.26(A) shall be from 3 to 5 feet, but the dedicated equipment space is only the width and depth of the equipment.
For example, a panelboard has been mounted on a concrete block wall. The structural ceiling is 6 feet above the top of the panelboard. There is nothing foreign to the electrical installation below the panelboard. An HVAC duct is in the same room as the panelboard, but it is not directly over it. The depth of the panelboard is almost 8 inches. The HVAC duct is against the structural ceiling, but it is 8 inches away from the wall with the panelboard mounted on it. While the HVAC duct is close to the dedicated zone, it is not within the dedicated zone. Therefore, this installation is permitted (see Figure 4).
Sometimes, suspended ceilings are located above panelboards or other equipment requiring dedicated space. In accordance with the exception to 110.26(E)(1)(a), this would be permitted under one condition. Suspended ceiling with removable panels shall be permitted within the 6-foot zone. For example, a panelboard is surface-mounted on a wall in an office building. There is a suspended ceiling above the panelboard (see Figure 5).
Next month’s column continues the discussion of requirements for electrical installations.