Article 110 provides general requirements for all installations. Section 110.22 provides the requirements for identification of disconnecting means.
Throughout Art. 110 and elsewhere in the Code, the adverb “legibly” is used in front of “marked.” Perhaps at some point, the Code will replace all of this repetition with a Subsection that provides the requirements for all markings. They must be legible, permanent, durable in the given environment, and visible (to maintenance people) on the installed equipment. For now, most of those requirements simply get repeated. Where they do not appear, common sense dictates that we follow them. What point is there in a marking that can’t be read?
So these apply to disconnects, even though not all of them are explicitly given in Sec. 110.22. Each disconnect must be marked with the purpose of the disconnect, for example “Motor 2391 Supply.” However, an exception to this rule exists when the disconnect is located and arranged so that its purpose is evident. For consistency in commercial and industrial applications, don’t omit the marking unless doing so offers some clear advantage other than a little cost avoidance. Why? It can be the “final defense” against misidentification.
Where the equipment has a circuit breaker or fuse applied in compliance with series combination ratings selected under engineering supervision per Sec. 240.86(A), the equipment must be marked with this information [Sec. 110.22(B) and (C)].
Disconnect markings are typically applied to the face of the enclosure. This is usually the best place. If the markings are applied to the handle, there is not much space to work with. Also, they are subject to being worn off. If the markings are applied to the side of the enclosure, you typically have ample space and protection from wear. But other equipment may be mounted (perhaps later) such that the markings won’t be readily visible.
Knife style disconnects with the knife switch handle on the right-hand side of the disconnect enclosure are commonly used with industrial motors. These have been around for a long time. One of their safety features is they are designed so the blast path is out through the front of the disconnect. It’s not a safety feature if the operator is standing in front of the disconnect. These should be mounted such that the operator stands to the right of the disconnect (where the switch is) and operates it with the left hand. This puts the operator’s face and body well outside the danger zone. Yet, people often operate these by standing in front of the disconnect and operating it with the right hand.
Given this problem, it’s a good practice to mark the disconnect with brief instructions such as “Stand to the right, operate with your left hand.” If space on the disconnect front does not permit that, it may be possible to place a sign above or to each side of the disconnect. Consider painting a red box on the floor, “Do not stand here to operate” and a green box “Stand here to operate” off to the side.
The NEC does not require these markings, probably because a qualified person should already know to operate a disconnect in this manner. But for disconnects that are likely to operate under load, adding these markings may save the life of someone operating it.
