Electrical Contractor

Article 110 has five parts. Part I covers general installation requirements. Part II covers electrical equipment with a nominal voltage of 600 volts (V) or less, and it starts with spacing requirements around electrical equipment.

For electrical equipment likely to require examination, adjustment, servicing or maintenance while energized, the working space shall not be less than the dimensions specified in 110.26(A)( 1) through (A)( 3). In accordance with 110.26(A)( 1), working space depth (in the direction of live parts) shall not be less than the minimum clear distances in Table 110.26(A)( 1) unless meeting the requirements in 110.26(A)( 1)(a), (A)( 1)(b), or (A)( 1)(c).

Table 110.26(A)( 1) specifies mini-
mum clear distances for working space
depth. This table is divided into two
rows. First-row distances are used
when the electrical equipment has a
nominal voltage to ground of 0–150V.

Regardless of the condition in the first row, the minimum working distance depth is 3 feet. Second-row distances are used when the electrical equipment has a nominal voltage to ground of at least 151V but not more than 600V. Some systems that would be included in this row include: 480Y/277V, three-phase, 4-wire system and 480/240V, three-phase, 4-wire system. This table also includes four columns. The first column shows the two electrical systems. The remaining columns are the three conditions for the electrical equipment. The conditions are explained below Table 110.26(A)( 1).

The first condition concerns where no live or grounded parts are across from the electrical equipment in which the depth of working space is being considered. If exposed live parts are on both sides of the working space but are effectively guarded by insulating materials, this first condition would also apply.

For example, a 480Y/277V, three-phase, 4-wire switchboard will be installed in an electrical room. The wall across the aisle from the switchboard will be covered in drywall. Because the drywall is not considered grounded, Condition 1 applies. The minimum working space depth for the switchboard in this installation is 3 feet (see Figure 1).

The second condition applies when grounded parts are on the other side of the working space. The second sentence in Condition 2 under Table 110.26(A)( 1) clarifies some surfaces, such as a concrete and concrete-block walls. Concrete, brick or tile walls shall be considered grounded.

For example, a 480Y/277V, three-phase, 4-wire switchboard will be installed in an electrical room. The wall across the aisle from the switchboard is concrete block. Because this wall is considered grounded, Condition 2 applies. The minimum working space depth for this switchboard is 3 feet, 6 inches (see Figure 2).

The third condition applies when exposed live parts are on both sides of the working space. For example, a 480Y/277V, three-phase, 4-wire switchboard will be installed in an electrical room. Across the aisle from this switchboard will be a 208Y/120V, three-phase, 4-wire switchboard. Because live parts could be exposed in both switchboards at the same time, Condition 3 applies.

The 208V switchboard needs only 3 feet of working space depth, but that is not enough working space for the 480V switchboard. The minimum working ILL

U S T R AT I O N S B Y C H A R L E S R . M I L L E R COD E IN F O C U S BY CHARLES R. MILLER

Article 110

UNDERSTANDING THE THIRD ARTICLE OF THE National Electrical Code (NEC), Article 110, Requirements for Electrical Installations, is essential to having a Code-compliant installation of the electrical system.

General Installation Requirements, Part XVIII
FIGURE 1 WORKING SPACE—CONDITION 1

The minimum working space depth for this electrical equipment is 3 feet.

The first condition under Table 110.26(A)( 1) is where exposed live parts are on one side of the working space and no live or grounded parts are on the other side of the working space or where exposed live parts are on both sides of the working space and are effectively guarded by insulating materials.