You’re reading an outdated article. Please go to the recent issues to find up-to-date content.
Electrical safety comes in many forms, for many different reasons, with the ultimate goal of ensuring a minimum of hazard for anyone working on electrical equipment. Electrical work is inherently dangerous, so when an accident occurs, every effort must be made to provide personal protective equipment for the individuals working on the electrical equipment.
Larger equipment usually means higher voltage with the inevitable increase in available fault current at the equipment, presenting an even greater hazard for anyone working in the proximity of the equipment. The travel distance to the nearest exit becomes critical when an electrical explosion occurs.
For the 1978 National Electrical Code (NEC) process, a proposal was accepted for Section 110-16 for working space about electric equipment requiring that “at least one entrance of sufficient area shall be provided to give access to the working space about electric equipment. For switchboards and control panels rated 1,200 amperes or more and over 6 feet wide, there shall be one entrance not less than 24 inches wide at each end where reasonably practicable.”
The Arizona chapter of the International Association of Electrical Inspectors submitted the proposal for inserting this text into the NEC with the following supporting comment for providing two means of egress from high amperage equipment: “This is necessary for the safety of the people working on the equipment or operating it. High amperage switchgear has more burning potential than high voltage. In the past, this has not always been done and arrangement of the equipment rooms has left much needed in the way of safety. Several people have almost burned to death when they were trapped in the back of such equipment rooms with the equipment burning between them and the only way out. (We should also see that equipment doors do not block exit ways from such areas.)” The original proposal was for equipment rated over 800 amps and more than 6 feet wide.
The basic text in this section remained relatively unchanged until the 2005 NEC. However, certain exceptions and additional text were added over time to permit one means of egress where the workspace in front of the equipment is doubled with the additional requirement that the equipment be located at least a minimum workspace dimension from the equipment to the nearest edge of the entrance into the area. An additional exception was added, allowing only one entrance where the location permits a continuous and unobstructed way of travel.
Section 110.26(C)(2) in the 2005 NEC was changed by deleting the requirement that equipment be more than 6 feet wide, leaving only the 1,200-ampere or more equipment requirement. This change, consequently, required two means of entrance for smaller dimension equipment, such as 1,200-amp or greater transfer switches, disconnect switches and individual circuit breakers installed in enclosures. This becomes a problem with existing installations where these devices must be installed as retrofits in equipment rooms where providing an additional entrance is not possible. The original reason for inserting the two means of entrance into the large equipment area was to deal with high amperage and wide equipment that would make travel past this equipment very dangerous where trying to access an entrance area as a means of escape from equipment.
There will be some very important changes coming for 110.26(C)(2) in the 2008 NEC. The title has been changed to cover both entrance and egress from the workspace. The “over 6 foot wide” requirement for 1,200-ampere and higher equipment has been reinserted into the text, and in addition, the text has been expanded to cover not only means of entrance to, but also egress from, the required working space. There is also a very subtle but extremely important change to this section that many people may not discover until they either design and install their first installation based on the changes to the text or they really study the new text.
The requirement for panic hardware, pressure plates or other devices for door hardware was moved from 110.26(C)(2) to new subsection 110.26(C)(3), “Personnel Doors.” The issue here is that previously, panic hardware and similar devices on personnel doors were limited to only those installations where the equipment was rated at 1,200 amperes or more and the equipment was wider than 6 feet. With this requirement moved to new subsection 110.26(C)(3), the panic door hardware requirement now applies to any door providing access to or egress from electrical equipment. However, an additional change in new subsection three requires this hardware on doors only where the door is less than 25 feet from the nearest edge of the workspace. Be sure that you study this change. EC
ODE is a staff engineering associate at Underwriters Laboratories Inc., in Research Triangle Park, N.C. He can be reached at 919.549.1726 or at [email protected].