b. Individual protection is not required where
such existing panelboards are used as service
equipment in supplying an individual residential
occupancy. For example, take a split-bus panelboard in
which the line section contains three to six circuit
breakers or fuses, none of which are rated 20 amperes or
less. In such an arrangement, one of the main
overcurrent devices supplies the second part of the
panel that contains l5- or 20-ampere branch-circuit
devices. The other main overcurrent devices (over 20
amperes) supply feeders or major appliances, such as
cooking equipment, clothes dryers, water heaters, or
air-conditioning equipment (fig. 5-4). Thisarrangement
is permitted only for existing panelboards in existing
individual residential occupancies.
2. A lighting and appliance branch-circuit
panelboard is limited to not over 42 overcurrent devices
(excluding the main overcurrent devices) in any one
cabinet or cutout box (fig. 5-5). When such devices are
numbered, a single-pole circuit breaker is counted as
one overcurrent device; a two-pole circuit breaker, as
two overcurrent devices; and a three-pole circuit
breaker, as three overcurrent devices.
In addition, the panelboards will be provided with
physical means to prevent the installation of more
overcurrent devices than the panelboard was designed,
rated, and approved to handle. Figure 5-6 shows a
suitable arrangement for overcurrent devices.
Figure 5-4.Typical arrangement of a split-bus lighting
Figure 5-5.Typical arrangement that shows NEC® rules for
Figure 5-6.Suitable arrangement for an existing 200-ampere
lighting panelboard used as service equipment for
individual residential occupancy.
A typical lighting panelboard is a circuit-breaker
type with a main 200-ampere circuit breaker and
thirty-two 20-ampere single-pole breakers. This type
of panel is used for a four-wire, three-phase, grounded
neutral system. The main breaker is three-pole.
Other NEC® provisions that apply to all types of
panelboards are as follows:
1. Panelboards, equipped with snap switches rated
30 amperes or less, will have overcurrent protection not
in excess of 200 amperes. Circuit breakers are not
considered snap switches.
2. Panelboards that have switches on the load side
of any type of fuse will not be installed except for use as
service equipment. Panelboard equipment with the snap
switch is on the line side of the plug fuses and satisfies