Understanding General Requirements of the NEC, Part 15

Article 110 provides general requirements for all installations. Part II provides the requirements for systems operating at 1,000V (nominal) or less. Section 110.27 covers the guarding of live parts. The NEC has two reasons for guarding live parts. One is to protect people from accidental contact. The other is to protect those parts from physical damage.

Installers are required to protect equipment from physical damage by arranging enclosures and guards that are of sufficient strength to provide that protection [Sec. 110.27(A)].

Installers are required to protect people from accidental damage by two strategies. One is to post warning signs at entrances to rooms and other guarded locations [Sec. 110.27(C)]. These signs must be conspicuous and forbid unqualified people to enter. They must meet the requirements of Sec. 110.21(B), which are essentially that they be permanently affixed and of sufficient durability to withstand the environment they are in.

The second strategy is to use approved enclosures or by implementing any of the four means listed in Sec. 110.27(A). Typically, an installer will use a combination of the enclosure and one or more of the four means. The four means are:

(1) Locate the equipment in a room, vault, or similar enclosure (enclosed space) that is accessible to only qualified persons.

(2) Use permanent, substantial partitions or screens to ensure that only qualified persons have access to the space within reach of live parts. Any openings have to be sized and located to preclude accidental contact by an unauthorized person.

(3) Locate the equipment on a balcony, gallery, or platform elevated and arranged so as to exclude unqualified persons. This technique is why there are so many small mezzanines throughout the typical production plant, and so is the fourth one.

(4) Elevate above the floor or other working surface to a minimum height of 8 ft, 8 ft 6 in., or 8 ft 7 in. for voltages of 50V to 300V, 301V to 600V, and 601 to 1000V respectively. Those voltages apply to the ungrounded conductors.

There’s one more aspect to this, and we find it in Sec. 110.26(F). When rooms or enclosures housing electrical equipment are controlled by locks, they are considered accessible to qualified persons. The point of the lock is to keep unqualified persons out and to keep the area from being used for storage or other non-electrical usage. File boxes and used lamps do not belong in an equipment vault, yet if the vault door is not locked you will eventually find such things in there.

It is typically company policy that the operations supervisors or superintendant(s) have a master key that opens all locks. After all, it is their job to run the place. But they are not qualified persons (for electrical work) and they have no need to enter an electrical equipment vault. Therefore, the master key should reside with maintenance, not with operations. If any room has a lock exclusively under maintenance control, it should also have signage that includes a contact number or other means of reporting smoke, noise, or other signs of problems.

What about rooms that house backup generators? Those rooms, and the generators therein, are typically under the control of the operators. They are not the same thing as a room dedicated to power distribution equipment such as transformers and panels. But inside those rooms, the same rules provided in Secs. 110.127(A), (B), and (C) apply to the guarding of live parts. You just can’t lock out operations from access to the room itself.