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.
Nongrounded surface 480V switchboard
151–600V
3 feet