Chapter 12 Branch Circuits and Feeders 147
Copyright Goodheart-Willcox Co., Inc.
• Branch circuits exceeding 120 volts but not
exceeding 277 volts may supply mogul-base
screw-shell lampholders, ballasts for fluorescent
lighting, ballasts for electric-discharge lighting,
plug-connected appliances, and hard-wired appli-
ances. Incandescent lighting operating over 150
volts is permitted in commercial construction.
• Circuits exceeding 277 volts and up to 600 volts
can supply mercury-vapor and fluorescent
lighting, provided the lighting units are installed
at heights not less that 22′ above grade and in
tunnels at heights no less than 18′.
Conductor Size and Ampacity
The amperage rating of branch-circuit conductors
must be greater than the maximum load the circuit will
provide. For multiple-load branch circuits, the conductor
ampacity must correspond to the rating of the overcurrent
protective device. However, for circuits supplying hard-
wired devices (such as electric heaters, air-conditioning
units, and water heaters), the fuse or circuit breaker can
be rated at the next higher rating. The conductor is
acceptable if its rating is at least that of the load current,
even if the overcurrent protective device rating is higher.
The smallest general-purpose conductor for branch
circuits is 14 AWG. Tap conductors can be smaller. See
Section 210.19 for more information.
Multiwire Branch Circuits
A branch circuit can be either a two-wire or multiwire
branch circuit. A multiwire branch circuit consists of a
grounded conductor and two or more ungrounded conduc-
tors. A multiwire circuit can be an individual circuit or a
multioutlet circuit.
Conductor Color Code
Grounded conductors of branch circuits are identified by
color. If the grounded conductor is 6 AWG or smaller, it is
white, gray, white with a color stripe, or has three continuous
white stripes on any color other than green insulation. If wires
from different systems are contained in the same raceway, the
neutrals of different systems are distinguished from one
another. For example, the neutral of one system would be
white, the neutral of the another system would be gray, and the
neutral of a third system would be white with a colored stripe.
The equipment grounding conductor must be green, green
with yellow stripes, or bare (without any insulation).
Hot conductors can be any color except white, gray,
green, and white with a color stripe. Normally, hot
conductors are black, blue, and red. In a three-phase,
four-wire delta system with a neutral connected at the
midpoint of a winding, the “high leg” phase conductor
should be identified with orange markings.
Branch-Circuit Loads
The Code places load limitations on branch circuits
with continuous loads (loads with a duration longer than
three hours, such as lighting). The continuous load must
not exceed 80% of the circuit rating allotted for it. If the
overcurrent protective device is listed for continuous
operation at 100% of its rating, the 80% factor is not used.
Branch-circuit loads are classified into five categories:
• Lighting loads.
• Receptacle loads.
• Equipment loads.
• Heating and cooling loads.
• Motor loads.
NOTE
Motor loads are discussed in Chapter 13 of this text.
Lighting Loads
In the broad sense, lighting loads may be categorized
as follows:
• General lighting.
• Show-window lighting.
• Track lighting.
• Sign and outline lighting.
• Other lighting.
Each lighting load is computed separately and then
combined to determine the total lighting load.
General lighting
General lighting is the overhead lighting within a
building. Its intensity should be adequate for any type of
work performed in the area. Determining the general
lighting load can be based on either the load per area
method or the actual full-load current of the fixtures used,
whichever is greater. Within a structure, there are normally
several different types of areas—storage, office, hallways,
and cafeterias—and these must be considered separately.
Most commercial structures have continuous lighting
loads and the branch circuits must be adequate for
carrying 125% of the calculated load. Code requirements
for general lighting loads are found in several sections:
• Section 220.12—Lighting Load for Specified
Occupancies
• Section 220.14—Other Loads—All Occupancies
• Section 220.16—Loads for Additions to Existing
Installations
• Section 220.18—Maximum Loads