The National Electrical Code (NEC) is full of rules and regulations that are intended to make electricity use safe. Consider the rules for sizing conductors and overcurrent protection. Without very specific rules for determining the right size conductor and the correct size overcurrent protective device, a conductor could overheat and start a fire, which could harm people and damage property.
Rules for access and working space are in place to make sure electrical equipment can be operated and maintained in a safe manner. Section 110.26 contains access and working-space requirements for electrical equipment operating at 1,000 volts (V), nominal, or less to permit ready and safe operation and maintenance of such equipment. The last heading in 110.26 pertains to locked electrical rooms or enclosures.
In many places throughout the Code, requirements state disconnecting means (such as fused disconnects and circuit breakers) shall be readily accessible. Although, that does not always mean it must be readily accessible to anyone and everyone. Section 110.26(F) states electrical equipment rooms or enclosures housing electrical apparatus that are controlled by a lock shall be considered accessible to qualified people.
Although this provision has been in 110.26 since the 2008 NEC, it lines up with the newly revised definition of readily accessible in Article 100. The definition of readily accessible was revised in the 2014 edition and again in the 2017 edition. In the 2014 NEC, the phrase “to actions such as to use tools” was added to the definition.
The 2014 edition defined readily accessible as capable of being reached quickly for operation, renewal or inspections without requiring those to whom ready access is requisite to actions such as to use tools, to climb over or remove obstacles, or to resort to portable ladders, and so forth. Adding a phrase about tools made it clear that, if a tool, such as a screwdriver, is used to remove a panel (or door), then electrical equipment behind that panel is not readily accessible.
There was a little confusion as to whether a key was considered a tool. In the 2017 edition, the phrase “(other than keys)” was inserted after the word “tools.” An informational note was added under the definition of readily accessible to help illustrate the use of keys, which states the use of keys is a common practice under controlled or supervised conditions and a common alternative to the ready access requirements under such supervised conditions as provided elsewhere in the NEC.
Circuit breakers in panelboards need to be readily accessible, but they can be readily accessible to qualified people only instead of everyone.
For example, two panelboards are located in a hallway inside an office building. The hallway is accessible to everyone during normal business hours. The doors on the panelboard enclosures contain a latch that is locked with a key, and only qualified people have the keys. Although the circuit breakers are not readily accessible to everyone who walks by, the circuit breakers are accessible to qualified people (see Figure 1).
Section 110.27 contains requirements pertaining to the guarding of live parts. Except as elsewhere required or permitted by the NEC, live parts of electrical equipment operating at 50 to 1,000V, nominal, shall be guarded against accidental contact by approved enclosures or by any of the means listed in 110.27(A)(1) through (4). The first method listed in this section states live parts can be guarded against accidental contact by keeping them in a room, vault or similar enclosure that is accessible only to qualified persons. The definition of readily accessible in Article 100 as well as the provision in 110.26(F) clarify that it is permissible to install electrical equipment behind locked doors as long as qualified people have keys so they can gain access to the electrical equipment.
For example, electrical equipment containing live parts have been installed in an electrical room. The doors to the room are always locked, but qualified people have keys to be able to get into the room to gain access to the electrical equipment. This installation is permitted because this electrical room is accessible only to qualified people (see Figure 2).
The second means listed in 110.27(A) states live parts can be guarded against accidental contact by permanent, substantial partitions or screens arranged so that only qualified people have access to the space within reach of the live parts. Any openings in such partitions or screens shall be sized and located so that nobody is likely to come into accidental contact with the live parts or to bring conducting objects into contact with them. Sometimes chain-linked fences are used to keep unqualified people out of areas containing live electrical parts. Although 110.27(A) does not mention work space in front of the live parts, 110.26(A)(1) requires a minimum depth of working space. 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).
For example, a chain-link fence is bolted to a concrete slab on the ground floor in front of live electrical equipment operating at 480V. Since the fence is grounded, the minimum clear distance as specified under condition 2 in Table 110.26(A)(1) is 3 feet, 6 inches.
The third means listed in 110.27(A) states live parts can be guarded against accidental contact by locating the electrical equipment on a balcony, gallery or platform elevated and arranged so as to exclude unqualified people. The fourth means listed in 110.27(A) states live parts can be guarded against accidental contact by elevation above the floor or other working surface in accordance with one of the elevations listed in 110.27(A)(4). The minimum elevation above the floor depends on the voltage of the electrical equipment. If the equipment is at least 50V but not more than 300V between ungrounded conductors, the minimum height shall be at least 8 feet. If the live parts of the electrical equipment are at least 301V but do not exceed 600V between ungrounded conductors, the minimum height shall be at least 8 feet, 6 inches. If the equipment is at least 601V but not more than 1,000V between ungrounded conductors, the minimum height shall be at least 8 feet, 7 inches (see Figure 3).
The second section under guarding of live parts pertains to protecting equipment from physical damage. In locations where electrical equipment is likely to be exposed to damage, enclosures or guards shall be so arranged and of such strength as to prevent such damage [110.27(B)]. Compliance with this requirement is mandatory whether the electrical equipment is indoors or outdoors. Requirements like this for protecting equipment from physical damage are in more than 200 sections throughout the Code.
The third section under guarding of live parts in 110.27 covers warning signs. Entrances to rooms and other guarded locations that contain exposed live parts shall be marked with conspicuous warning signs forbidding unqualified people to enter. This section does not specify the wording on the warning sign comparable to the danger-sign requirement in 110.34(C) for exposed live parts operating at over 1,000V, nominal. It requires the marking to meet the field-applied hazard-marking requirements in 110.21(B). The first subsection in 110.21(B) states the marking shall warn of the hazards using effective words, colors, symbols or any combination thereof. The second subsection states the label shall be permanently affixed to the equipment or wiring method and shall not be handwritten. Since 110.27(C) requires a warning sign at the entrance to rooms or other guarded locations that contain live parts, the warning sign must be permanently affixed to (or at) the entrance, which could be a door, fence, gate, etc. The third subsection under 110.21(B) states the label shall be of sufficient durability to withstand the environment.
The informational note under 110.27(C) refers the user to see 430.232 and 430.233 for exposed live parts of motors and controllers. The note also states to see 110.34 for electrical equipment over 1,000V.
Next month’s column continues the discussion of electrical installation requirements.