Over the past few months, we have discussed how good electrical design practice cannot and should not ignore the safety implications associated with the electrical installation. Where the stated purpose of the Code is enhanced (i.e., “the practical safeguarding of persons and property”), good design practice compliments the entire electrical installation and should be mandated.
In some cases, this extends beyond what is traditionally considered the scope of the electrical system. For example, the very placement of the equipment, such as the construction of the room where it is located, can dictate the safety of the installation. Article 110, Requirements for Electrical Installations, is replete with these types of requirements. Working space, illumination, and clear spaces are all attempts to ensure personnel servicing electrical equipment safety.
For several Code cycles, Code Making Panel 1 (CMP-1) has struggled with another issue. Section 110-26 contains important requirements for defining and maintaining working space about electrical equipment, which is likely to require servicing, examination, adjustment, or maintenance while in an energized condition. Associated with the issue of working space is access to and egress from such spaces.
There is no need to look back any further than the 1999 NEC cycle to understand the main issues involved in the debate. Proposal 1-248 suggested adding a new paragraph to Section 110-16(c) (Section 110-26(c) in the 1999 NEC), which reads as follows: “(D)oors providing access to a room(s) or enclosure(s) containing Service Equipment shall be provided with panic hardware.”
The purpose of the panic hardware is to facilitate the quick exit from the working space in the advent of an electrical accident or emergency. The substantiation reasoned that the presence of service equipment would indicate the possibility of increased levels of fault current and the presence of conductors, which may be provided with significantly less overcurrent protection.
Another proposal was for panic hardware only to be required for “doors in electric rooms with a Kva rating of 750Kva or more.” The submitter argued that there is precedent in the Code for panic hardware in Section 450-43(c). This section requires “personnel doors shall swing out and be equipped with panic bars, pressure plates, or other devices that are normally latched but open under simple pressure.”
Unfortunately, CMP-1 rejected this and similar proposals because they felt that 450-43(c) addressed requirements particular to transformer installations. “Section 450-43(c) as well as other sections within Part C of Article 450 are special requirements for transformer vaults, which involve unique fire and life safety hazards. The provisions are based upon other fire safety standards that have addressed the risks associated with transformer vaults. A similar risk with electric equipment has not been documented.”
Increasingly, more and more light is being shed on the hazards of working on or near energized electrical conductors and equipment. The long-familiar hazards of fire and electrical shock are no longer the only considerations. Recent studies have shown that additional concerns must include the damaging effects of arc-blasts and arc-flashes. Consideration must be given to the devastating forces generated in arc-blasts when molten copper expands to 67,000 times its original value as it vaporizes. Likewise, arc temperatures can reach 35,000 degrees Fahrenheit, causing fatal burns at distances up to 10 feet. Furthermore, the pressure wave generated by the blast can reach upwards of 2,000 pounds per square foot, certainly enough pressure to rupture the eardrums or even collapse the lungs. It is especially important to consider that, as our electrical distribution systems continue to grow in size and capacity, the potential for higher and higher available fault currents and significantly greater arc-blasts and arc-faults rises sharply.
Obviously, these concerns extend beyond just the hazard of fire. In these cases, it is critical that personnel be able to quickly exit the working space and seek medical assistance. Doors that swing out, in the direction of egress and that are easily opened, can greatly assist a worker who has received an electrical or thermal burn to his or her hands and needs quick medical attention.
2002 NEC cycle
CMP-1 revisited the issue for the 2002 NEC. In a panel proposal, CMP-1 has made several proposed revisions to Section 110-26(c)(1). The most substantive change is a new last sentence to (c) (2), which reads, “Where the entrance has a personnel door(s), the door(s) shall open in the direction of egress and be equipped with panic bars, pressure plates, or other devices that are normally latched but open under simple pressure.”
The panel substantiation for this portion of the proposal stated that the “panel recognizes that the safety of workers who are exposed to energized conductors is of great concern. The revision will limit the application of the requirement for panic hardware to personnel doors to workspaces where doors are provided.”
Interestingly, CMP-1 used the same requirement in Section 110-33(A) for entrance and access to working space over 600-volts nominal. This parallel construction of similar types of requirements is very helpful in both application and interpretation in the field.
CMP-1 has done an excellent job at providing a framework to settle this long-standing controversial proposal. First, the requirement must be considered in light of its placement in a new section, “(c) (2) Large Equipment.” This section only applies to equipment rated 1200 amperes or more or over six feet in length. The section is intended to apply to equipment that contains overcurrent devices, switching devices, and other control devices. By placing the requirement in this section, CMP-1 found a way around the long-standing problems of attempting to define an electrical equipment room and specifying what doors would require panic hardware. Under the proposal, the panic hardware requirement will only apply to doors where this type of “large” equipment is present. There is a much greater assurance that where such equipment is used, it will be installed in an electrical equipment room with doors specifically for access to the equipment. The proposal also takes into consideration that in some cases, a standard door is not used to gain access to the working space. Often for example, a large overhead door may be installed for ease of equipment installation. The wording of the proposal specifically limits the requirement to personnel doors. Finally, CMP-1 gave some latitude to the designer. Pressure plates, panic bars, and other similar types of devices are all acceptable provided they afford personnel a quick means of exit without requiring undue pressure to defeat the latch mechanism.
CMP-1 has tackled a tough issue: one that clearly impacts safety and one that falls squarely within the stated purpose of the Code. This proposal is a clear compromise in that the scope of the requirement is limited to “large equipment.” At the same time, it is a much more workable solution than requiring panic hardware wherever any electrical equipment is installed. This proposal provides a starting point for ending a long-standing debate.
Electricians frequently must work on or near energized electrical conductors or equipment because it is infeasible, or it would create a greater hazard, to de-energize the equipment. Such decisions should be made only after a complete job safety hazard analysis has been performed. But, when such work is deemed necessary, the workers ought to be able to count on a quick exit from the working space. This proposal provides that assurance.
CALLANAN is director of Safety, Codes, & Standards at the National Joint Apprenticeship & Training Committee. He can be reached at email@example.com.