Raceways, except surface-metal molding, must be installed as complete empty systems, the conductors being drawn in later. Conductors must be continuous from outlet to outlet without splice. except in auxiliary gutters and wireways.
Conductors of No. 8 AWG and larger must be stranded. Raceways must be continuous from outlet to outlet and from fitting to fitting and will be securely fastened in place.
All conductors of a circuit operating on alternating current, if in a metallic raceway', should be run in one enclosure to avoid inductive overheating. If, owing to capacity, not all conductors can be installed in one enclosure, each raceway used should contain a complete circuit (one conductor from each phase).
Rigid-metal conduit, intermediate metal conduit, and electrical metallic tubing are the systems generally used where wires are to be installed in raceways. Both conduit and tubing may be buried in concrete fills or may be installed exposed. Wiring installed in conduit is approved for all classes of buildings and for voltages both above and below 600 volts. Certain restrictions are placed on the use of tubing; refer to the NEC® .
Lighting and power systems start at the panelboards. Refer to the NEC® during the installation of the lighting and power circuits for further guidance. The wiring layout in each of these illustrations determines how the component parts in the circuit will be connected to one another and where the wires will be routed. Careful planning in the wiring layout can result in substantial savings by eliminating long runs of excess wire. It should be pointed out that the wire runs that are shown in the actual construction illustration may not be the most economical use of wire. These wire runs are laid out in a very smooth and definite pattern to make the drawing easier to follow. In many cases, wire runs shown at right angles should be run diagonally to conserve wire. When cable runs are routed on the jobsite, shortening the runs will result in lower installation costs.
No limit is placed on the electrical capacity of service conductors and service protection used in bringing the electric supply into a building, since only one supply should be introduced whenever possible. Near the point of entrance of the supply, the heavy- service conductors are tapped by feeders that conduct the electricity to panelboards at various load centers in the building where the final branch circuits which supply individual lighting, heating, and power outlets originate. No limits are placed on the electrical capacity of feeders; but, for practical purposes, they are limited in size by the difficulty of handling large conductors and raceways in restricted building spaces, by voltage drop, and by economic considerations.
Each lighting fixture, motor, heating device. or other item of equipment must be supplied by either a branch circuit for grouped loads, by an individual branch circuit, or by a motor branch circuit.
In solving all installation problems with panelboards, the first consideration is to determine whether the panelboard will be considered a lighting and appliance branch-circuit type. The NEC® rules are much stricter for lighting and appliance branch-circuit panelboards than for other types.
The Code defines a lighting and appliance branch- circuit panelboard as one having more than 10 percent of its overcurrent devices rated 30 amperes or less for which neutral connections are provided. For example, if any panelboard with less than 10 overcurrent devices contains one overcurrent device rated at 30 amperes for which neutral connections are provided, it would be considered a lighting and appliance branch-circuit panelboard (1 9 = 11%).
In another example, panelboards that supply loads without any neutral connections are not considered lighting and appliance branch-circuit types whether or not the overcurrent devices are 30 amperes or less.
When it is determined that a panelboard is a lighting and appliance branch-circuit type, the following NEC® rules apply:
1. Individual protection, consisting of not more than two main circuit breakers or sets of fuses having a combined rating not greater than that of the panelboard, is required on the supply side. This main protection may be contained within the panelboard or in a separate enclosure ahead of it. Two exceptions to the Code rule are as follows:
a. Individual protection is not required when the panelboard feeder has overcurrent protection not greater than that of the panelboard. For example, two 400-ampere panelboards can be connected to the same feeder if the feeder overcurrent device is rated or set at 400 amperes or less.Continue Reading