It is extremely important to provide a safe and clear means of egress from electrical equipment and to ensure a worker’s ability to quickly exit an area during an electrical explosion and fire. The 2002 National Electrical Code (NEC) has added some necessary requirements to provide that safety.
Section 110.26(C) requires at least one entrance of sufficient area be provided to give access to the working space around electrical equipment. The entrance to the working space around electrical equipment does not necessarily mean a door access, although it often does. The entrance can be a clear space within a much larger room that permits easy access to and egress from the electrical equipment.
For large electrical equipment containing overcurrent devices, switching devices or control devices, having a safe and clear means of egress is critical. Where large equipment is rated at 1,200 amperes or more and is more than 6 feet in width, there must be one entrance at each end to the required working space. These entrances must not be less than 24 inches wide and must be at least 6 1/2 feet high. There are some exceptions, however, that permit only one means of egress. Where the depth of the working space in front of the equipment is doubled, or where the location of the electrical equipment permits a continuous and unobstructed exit, a single entrance is permitted.
By providing dimensions for the means of egress, the NEC sets the minimum size of the egress area and helps prevent a bottleneck that could effectively trap a person trying to exit during an emergency situation. Panic and the inability to quickly exit an area could have tragic consequences.
The new text on means of egress that has been added to the 2002 NEC closely parallels one of the requirements contained in Section 450.43 covering doorways for transformer vaults in Part III of Article 450. Section 450.43(C) requires vault doors to be equipped with panic bars, pressure plates, or other devices that are latched but open under simple pressure. The door must also swing out of the vault, not into the vault. There are some other requirements in Section 450.43, such as the type of doors, the fire rating of the door, and the access by qualified personnel only, that has not been inserted into Section 110.26(C) yet, but may show up in the 2005 NEC process as Proposals.
Recognizing that the same hazards in transformer vaults can exist in large equipment locations, NEC Code Making Panel One has inserted text involving personnel doors. Where the electrical equipment is rated at 1,200 amps or more and is more than 6 feet wide and a personnel access door is provided, it must open in the direction of egress. These doors must also be equipped with panic bars, pressure plates, or other devices that are normally latched but will open under simple pressure. This applies only to large-equipment access where an egress door is supplied.
The purpose is to provide an easy means of egress out of a closed and latched door during an emergency. The person attempting to egress may have burns or other disabling injuries making it difficult or impossible to open a door with normal hardware or where the door must be opened into the room. If an electrical explosion occurs, a person can use an arm or other body part to open the door.
If the equipment door opens into a hallway used as building egress, the local building codes or NFPA 101, the Life Safety Code, may require the doorway to be recessed in the wall such that the door opening will not impede people attempting to leave the building. Recessing the door opening will also keep people in the hallway from being injured by a sudden door opening.
These NEC changes will affect the construction industry and should be recognized by architects, structural engineers, electrical engineers, municipal plan reviewers, structural inspectors and electrical inspectors at an early stage of building design. This change will affect new buildings and those being remodeled where doors are being added or where electrical equipment may be increased in size and ampacity to fit within the large equipment dimensions.
Since electrical inspectors and contractors are most familiar with the NEC, it is imperative they alert other industry members affected by this change. It is easier to make changes during design than during construction and will ensure implementation. 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 firstname.lastname@example.org.