NEC Article 210 - Branch Circuits
Article 210, Branch Circuits*
This Article contains Table 210.2, which identifies specific-purpose branch circuits. When people complain that the Code "buries stuff in the last few Chapters and doesn’t provide you with any way of knowing," that is usually because they didn’t pay attention to this table.
NEC 210.4 Multiwire Branch Circuits. This is a circuit that "consists of two or more ungrounded conductors that have a voltage between them, and a grounded conductor that has an equal voltage between it and each ungrounded conductor of the circuit, and that is connected to the neutral or grounded conductor of the system." The conductors of such circuits must originate from the same panel. These circuits can supply only line-to-neutral loads.
NEC 210.8 Ground-Fault Circuit-Interrupter Protection for Personnel. Crawl spaces, unfinished basements, and boathouses are just some of the 8 locations requiring GFCI protection. If you don’t know the others, you’ll find out what they are in 210.8. (Click here for more on how GFCI's work)
NEC 210.11. Branch Circuits Required. With three subheadings, 210.11 gives summarized requirements for the number of branch circuits in a given system, states that a load computed on a VA/area basis must be evenly proportioned, and covers rules for dwelling units.
NEC 210.12. Arc-Fault Circuit-Interrupter Protection. An AFCI provides "protection from the effects of arc faults by recognizing characteristics unique to arcing and by functioning to de-energize the circuit when an arc fault is detected." It is not a GFCI, though they do trip out on a ground fault, such as mixing neutrals with another circuit. The purpose of an AFCI is to detect arcing that could ignite into a fire. (Click here for more on how AFCIs work as well as installation and troubleshooting tips) also, NEMA and UL have a free online class to help install and troubleshoot AFCI circuits (Click here for more info on this class).
NEC 210.19. Conductors—Minimum Ampacity and Size. The rules for ampacity require some study. One item many overlook is that branch conductors—before the application of any adjustment or correction factors—must have "an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load." The Code does have an exception for this, but the rule generally applies.
NEC Table 210.21(B)(2) shows that the maximum load on a given circuit is 80% of the receptacle rating and circuit rating.
NEC 210.23 Permissible Loads. Read on down to (A)(2): "Utilization Equipment Fastened in Place. The total rating of utilization equipment fastened in place, other than luminaries (lighting fixtures) shall not exceed 50 percent of the branch-circuit ampere rating where lighting units, cord-and-plug-connected utilization equipment not fastened in place, or both are also supplied." The idea here is to prevent a circuit overload just because someone plugs in a lamp or vacuum cleaner. Proper planning and good engineering practices will prevent needing to be concerned with this aspect of the Code. Place lights on separate circuits, dedicated (fastened in place) loads on separate circuits, and convenience receptacles on separate circuits. The added cost really isn’t that much. In residential construction, the goal is to build as cheaply as possible. However, if presented to Realtors and buyers correctly, a good electrical plan (vs. the standard plan, which may meet Code but is barely functional) will provide a selling edge. Even if the sale price isn’t higher, the number of days on the market will be less and cash flow will improve.
NEC Table 210.24 Summary of Branch-Circuit Requirements allows you to see everything at a glance. You just look up the circuit rating (which you will base on the load you plan to supply), and the table tells you the minimum conductor size. For that circuit rating, it also tells you the size of the taps, overcurrent protection, and maximum load. It also tells you which lampholders are permitted, and what the receptacle rating must be. Don’t leave home without it!
NEC 210.52. Dwelling Unit Receptacle Outlets. In habitable rooms, "Receptacles shall be installed so that no point measured horizontally along the floor line in any wall space is more than 1.8 meters (6 feet) from a receptacle outlet." This means you can’t have receptacles more than 12 feet apart along a wall line. 210.52 notes certain exclusions, describing what a wall space is and is not. The Code does not prohibit having more receptacles than the minimum requirment, but, you cannot space them any less than 12 feet apart along a wall. Note, doorways and some other items do not count in the 12 feet.
*Quoted text is taken from the 2011 edition of the NEC. Information presented here is not intended as a substitute for the NEC.