3. The total load on any overcurrent device,
located in a panelboard, will not exceed 80 percent of its
rating. If in normal operation, the load will be
continuous (3 hours or more) unless the assembly
including the overcurrent device is approved for
continuous duty at 100 percent of its rating.
Power-distribution panels are similar to the
feeder-distribution type. They have bus bars normally
rated up to 1,200 amperes at 600 volts or less and
contain control and overcurrent devices sized to match
connected motor or other power circuit loads.
Generally, the devices are three-phase.
Special panelboards. containing relays and
contactors, can be obtained and installed when remote
control of specific equipment is specified. A thorough
knowledge of all the available types of panelboards
aids in the selection and installation of the proper unit.
Service-equipment panelboards, for loads up to
800 amperes, containing six or fewer main fused
switches, fused pullouts, or circuit breakers are
available. These panels constitute service equipment
and frequently contain split buses that supply branch
circuit or feeder overcurrent devices installed in the
same enclosure (figs. 5-4 and 5-6).
Feeder distribution panels generally contain
circuit overcurrent devices rated at more than 30
amperes to protect subfeeders that extend to smaller
BRANCH CIRCUITS FOR
The uses and limitations of the common types of
branch circuits are outlined in the Summary of Branch-
Circuit Requirements (NEC® table 210-24). Lighting
branch circuits may carry loads as high as 50 amperes,
although florescent lighting is limited to use on circuits
of 15-ampere or 20-ampere rating. Such circuits are
extensively used in commercial and industrial
occupancies. Branch circuits, supplying convenience
outlets for general use in other than manufacturing
areas, are usually limited to a maximum of 20 amperes.
The type of outlet required for heavier capacity circuits
usually will not accommodate the connection plug
found on portable cords, lamps, motor-driven office
machinery, and so forth.
INDIVIDUAL BRANCH CIRCUITS
Any individual piece of equipment (except
motors) also may be connected to a branch circuit
meeting the following requirements: Conductors must
be large enough for the individual load supplied.
Overcurrent protection must not exceed the capacity of
the conductors or 150 percent of the rating of the
individual load if the single-load device is a nonmotor-
operated appliance rated at 10 amperes or more. Only a
single outlet or piece of equipment may be supplied.
MOTOR BRANCH CIRCUITS
Because of the peculiar conditions obtained during
the starting period of a motor and because it may be
subjected to severe overloads at frequent intervals,
motors, except for very small sizes, are connected to
branch circuits of a somewhat different design from
that previously discussed.
The Code covers general requirements for
conductors and their type designations, insulations?
markings, mechanical strengths, ampacity ratings, and
uses. These requirements do not apply to conductors
that form an integral part of the equipment, such as
motors, motor controllers, and similar equipment, or to
conductors specifically provided for elsewhere in the
Conductors must be insulated except where
covered or bare conductors are specifically permitted
by the NEC®. The Code covers the insulation of
neutral conductors of a solidly grounded high-voltage
system. When stranded conductors are installed, the
Code states that stranded conductors installed in
raceways must be a size No. 8 or larger with the
Exception No. 1:
When used as bus bars or in
mineral-insulated, metal-sheathed cable
Exception No. 2: When bonding conductors are
Conductors in Parallel
Aluminum, copper-clad aluminum, or copper
conductors of size 1/0 and larger, in each phase of the
current; neutral; and grounded circuit conductors may
be connected in parallel (electrically joined at both
ends to form a single conductor).
Exception No. 1: Conductors in sizes smaller than
No. l/O AWG will be permitted to run in parallel to
supply control power to indicating instruments,
contactors, relays, solenoids, and similar control
1. They are contained within the same raceway or