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Determining Working Clearances

Aug 1, 2001 12:00 PM, By James Stallcup, Sr., NEC Consultant

Are you protecting yourself from electric shock and burns? You're not if you fail to comply with the following three clearance requirements in Sec. 110-26 of the National Electrical Code (NEC): 1) at least a 3-ft clearance in front of all electrical equipment; 2) a 30 in.-wide working space in front of equipment operating at 600V or less; and 3) minimum headroom clearance of 6 ft or the height of the equipment, whichever is greater. Let's look at these three clearances in detail.

Depth of working space Sec. 110.26(a)(1)

The depth of the working space in front of exposed live parts must be at least as great as the distances outlined in Table 110-26(a). You must measure distances from live parts or from the front of the enclosure or opening in which the live parts are enclosed. The working clearance in front of the equipment on which you're working is also dependent on the composition of the facing wall and whether it houses live electrical parts. As you'll note in the Table, there are three conditions noted for two voltage levels 150V or less and 151V to 600V-to-ground. For example, the clearances of a 120V/208V, 3-phase, 4-wire system fall under the 150V-to-ground or less category while a 277V/480V, 3-phase, 4-wire system falls in the 151V- to 600V-to-ground classification. The text below Table 110-26(a) explains the application and use of all three conditions.

Condition 1, Table 110-26(a)

Condition 1 describes a situation in which the electrical equipment is installed in or on a wall that faces an insulated wall, constructed of wood or metal studs, and sheetrock or wood panels. If you make contact with the insulated wall while touching live parts of the equipment, you're isolated from the grounded slab or earth. Therefore, Condition 1 allows for a reduced working space. Before the 1965 NEC, Condition 1 only required a 2-ft workspace in front of electrical equipment.

Condition 2, Table 110-26(a)

Condition 2 pertains to a situation in which the electrical equipment is installed on a wall that faces a conductive (grounded) wall. A conductive (grounded) wall (made of concrete, brick, or tile) can connect the body to ground if touched. If you make contact with this type of wall while touching a live part or conductor, you will create a circuit path to ground, which could lead to electrocution. Because this danger is present, the Code requires a larger workspace when voltages range from 151V to 600V.

Condition 3, Table 110-26(a)

Condition 3 exists when the electrical equipment is installed in or on a wall that faces another wall of electrical equipment. With electrical equipment installed in this manner, there are live parts on both sides of the room. In this case, you may be subjected to phase-to-phase voltage or phase-to-ground voltage when servicing the equipment. Because you could be exposed to a fatal shock from live parts on either side of the workspace, the NEC requires a greater clearance for your safety.

Width of working space Sec. 110-26(a)(2)

This space requirement creates sufficient room for you to work on the equipment without contacting live parts and metal parts. You must also provide for a 90 opening of equipment doors and hinged panels in the workspace. This allows you to have adequate room to repair, adjust, or reset overcurrent protection devices without placing your body between the panel door and the panelboard. This requirement first appeared in the 1987 NEC.

Height of working space Sec. 110.26(a)(3)(e)

As a general rule, you must maintain a minimum headroom clearance of 6 ft from the floor or platform up to any overhead obstruction. This workspace is mandatory and applies to service equipment, switchboards, panelboards, and motor control centers. The overhead workspace protects employees from accidentally touching grounded objects and exposed live parts at the same time. As mentioned earlier, this act would complete a circuit to ground connection, which could cause a fatal electric shock. In addition, electricians or maintenance workers should never have to stoop or bend down to gain access to service, repair, or modify components inside electrical equipment.

Summary

While trying to adhere to these requirements, it's easy to lose sight of what you're going to all this trouble for: You install electrical equipment with adequate workspace for the safety of those servicing it. This workspace is required and must be maintained around all electrical equipment where parts of an energized system may be serviced. Before designing workspaces with clearances less than those described in this article, consult with the authority having jurisdiction (AHJ) and ask for a variance in writing.

Workspace Origins

Installations built before the 1978 NEC only require a minimum clearance of 2 ft in front of electrical equipment. The 30-in.-wide rule has been used since the 1971 NEC. Headroom clearance has been required since the 1965 NEC.

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