sure that good installation practices have been observed and all connections are correct. While you are making this check, do not forget neatness. Make sure that ground connections are tight and that ground wire is protected against injury. Be sure that all connections in the entrance switch and panelboards are tight. See that all metal noncurrent-carrying parts of portable equipment are grounded
The service entrance terminates in the service equipment or in a panelboard. The panelboard may be used for lighting and power branch circuits. A distribution panel, as the name implies, serves as a center or point in the electrical system where power is fed to the branch circuits. A distribution panel consists mainly of a metal cabinet that houses bus bars and individual circuit protective devices. The protective devices (fuses or circuit breakers) protect me circuits against excessive current flow. Panelboards must be rated at least as high as the feeder capacity required for the load. Panelboards are marked by the manufacturer with the voltage, current rating, and number of phases for which they are designed. This information, plus the manufacturer's name or trademark, is not to be obstructed by interior parts or wiring after the panelboard is installed.
According to the NEC, lighting and appliance panelboards cannot have more than 42 overcurrent devices besides the mains. Two- pole and three-pole circuit breakers are connected as two and three overcurrent devices, respectively. According to the NEC, each lighting and appliance panelboard must be protected from current flow on the supply side by not more than two main circuit breakers or two sets of main fuses that have a combined rating no greater than that of the panelboard. This protects not only the feeders but also the panelboard. The panelboard does not need individual protection if the panelboard feeder has overcurrent protection no higher than the panelboard rating. The total load on any single overcurrent device in a
Figure 5-61. - Plug type of fuse.
panelboard must not exceed 80 percent of its capacity where, in normal use, the load continues for 3 hours or longer to prevent overheating of the conductor.
Panelboard cabinets must be grounded. A terminal bar must be provided for attachment of feeder and branch circuit equipment-grounding conductors where nonmetallic raceway or cable is used. This terminal bar must be bonded to the cabinet, but not to the neutral bar except in service equipment.
Three-phase panelboards supplied by a four-wire, delta-connected system that has the midpoint of one phase grounded must have the higher voltage-to-ground conductor or bus bar marked. This high-voltage conductor should have an orange outer finish or be clearly tagged. The identification is required at any point where a connection can be made and the neutral conductor is also present. The phase arrangement on a three-phase panelboard is A, B, C, from left to right, or top to bottom when viewed from the front. The B phase will be the phase that has the higher voltage-to-ground.
There are two basic types of panelboards: fuse panels and circuit breaker panels. Fuse panels, as the name implies, contain fuses for protection of each circuit. Fuse panels are designed in a variety of ways. These designs vary in size, capacity (amperage and voltage), and type of installed fuses. The capacity of the panel is based on the ampacity of the bus bars of the panel. The number of bus bars is determined by whether the panel is single-phase or three-phase. Fuse panels are designed for plug fuses, cartridge fuses, knife-blade fuses, or a combination of these. Fuse panels use an Edison-base fuse that screws into a socket similar to the medium-based light socket. Fuse panels still exist but are not very common. Fuse panels are not to be installed either for new work or as a replacement panel unless they have been modified to accept Type S fuses. Refer to figure 5-61 for a view of the plug type of fuse and figure 5-62 for a view of the adapter and Type S fuse.
Figure 5-62. - Adapter and Type S fuses.Continue Reading