Since it first appeared in the 1953 National Electrical Code (NEC) as Sec. 3881 until the 1999 edition in Sec. 384-14(a) it was never quite clear just what constituted a “lighting and appliance branch-circuit panelboard.”
The 1996 NEC and earlier versions read: “For the purposes of this article, a lighting and appliance branch-circuit panelboard is one having more than 10 percent of its overcurrent devices rated 30 amperes or less, for which neutral connections are provided.” The uncertainty was in whether these “30 amperes or less” circuits qualified as “lighting and appliance branch circuits,” whether they actually used the neutral connection, or whether the neutral connection was there (provided) but not actually used.
The 1999 NEC has finally cleared up this uncertainty by defining a “lighting and appliance branch circuit” as one having a connection to the neutral and that has overcurrent protection of 30 amperes or less in one or more conductors. Now a lighting and appliance branch circuit panelboard is one having more than 10 percent of its overcurrent devices protecting 30 ampere or less branch circuits, which have neutral connections.
A new designation has been created: “Power Panelboard,” which avoids the cumbersome expression “other than a lighting and appliance branch circuit panelboard,” which has been in the code for years, while in the field they have been called “power panels.” A power panelboard is defined in Sec. 384-14(b) as “one having 10 percent or fewer of its overcurrent devices protecting lighting and appliance branch circuits,” already defined as 30-ampere-or-less circuits having neutral connections.
The requirement in Sec. 384-15 limiting the number of overcurrent devices in a lighting and appliance branch circuit panelboard to 42 (other than the mains) is unchanged, and this 42-pole limit does not apply to power panels.
Also unchanged is Sec. 384-16(a), which requires that each lighting and appliance branch-circuit panelboard be individually protected by not more than two circuit breakers or two sets of fuses.
New in the ’99 NEC is 384-16(b):
“(b) Power Panelboard Protection. In addition to the requirements of Section 384-13, a power panelboard with supply conductors that include a neutral and having more than 10 percent of its overcurrent devices protecting branch circuits rated 30 amperes or less shall be protected on the supply side by an overcurrent protective device having a rating not greater than that of the panelboard.
Exception: This individual protection shall not be required for a power panelboard used as service equipment with multiple disconnecting means in accordance with Section 230-71.”
This presents us with a second category of power panelboard, [not the one defined in 384-14(b) as one having 10 percent or fewer of its overcurrent devices protecting lighting and appliance branch-circuits] having more than 10 percent of its overcurrent devices protecting branch circuits of 30 amperes or less where the feeder includes a neutral, but these branch circuits need not necessarily connect to the neutral.
This is precisely the 1996 definition of a lighting and appliance branch-circuit panelboard, except that this new “power” panelboard must be protected from overcurrent at its rating, a more stringent requirement than that for a lighting and appliance branch-circuit panelboard that is permitted two circuit breakers or two sets of fuses ahead of it.
What we are left with is no requirement for overcurrent protection for a power panelboard as defined in Sec. 384-14(b) with 10 percent or fewer of its overcurrent devices protecting lighting and appliance branch circuits. This means that the requirements in Secs. 430-62(a) and 430-63 can be used, where one or more large motors requires that the overcurrent protection for the power panel, or for the feeder to it, can be rated larger than the ampacity of the feeder conductors. This is necessary in order to allow a large motor to start, while permitting the feeder conductors or the panelboard rating to handle the running current without needing to be oversized.
This conclusion is not immediately clear based on the words in the Code, but it makes sense in that a power panel as defined in Sec. 384-14(b) is treated with regard to rating and overcurrent protection in the same way as we have always done in the past. No doubt many Code users will grasp at the heading of Sec. 384-16(b) and attempt to protect all power panels at their rating, which may be neither necessary nor practical.
SCHWAN is an electrical code consultant in Hayward, Calif. He can be reached via e-mail at firstname.lastname@example.org.