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210-21(b) Receptacles
A “Receptacle,” as defined in Article 100, is a contact device installed at an outlet for the connection of an attachment plug. The words “receptacle” and “receptacles” appear quite often in the National Electrical Code (NEC).
In fact, they appear more than 250 times. Although receptacles are manufactured in a wide variety of configurations and sizes, usually the first thing that comes to mind when we think of a receptacle is a 15-or 20-ampere, 125-volt duplex receptacle. Although it is a single device, it is not considered a single receptacle.
Article 100’s definition of a receptacle also states that a single receptacle is a single contact device with no other contact device on the same yoke. A multiple receptacle is two or more contact devices on the same yoke. Since a duplex receptacle contains two contact devices, it is a multiple receptacle, not a single one.
Receptacles installed on 15- and 20-ampere branch circuits must be of the grounding type unless meeting the provisions in 210-7(d). Section 210-7(d) covers requirements for replacing existing receptacles.
(Receptacle replacement provisions were explained in the August 2001 issue.) Receptacles must be installed only on circuits of the voltage class and current for which they are rated, except as provided in Tables 210-21(b)(2) and (b)(3). [210-7(a)]
210-21(b)(1) Single Receptacle on an Individual Branch Circuit
A single receptacle installed on an individual branch circuit must have an ampere rating equal to the rating of that circuit. [210-21(b)(1)] An individual branch circuit supplies only one piece of utilization equipment. A single receptacle installed on a 15-ampere branch circuit must have a rating of 15 amperes, while one installed on a 20-ampere branch circuit must have a rating of 20 amperes. As mentioned earlier, a single receptacle is a single contact device with no other contact device on the same yoke.
Dwelling units require at least one receptacle outlet for the laundry area. [210-52(f)] Laundry receptacle outlets in dwelling units must be fed from a 20-ampere branch circuit. Receptacle outlets outside of the laundry area are not permitted on the laundry circuit. [210-11(c)(2)]
If the laundry receptacle is a single receptacle and it is the only receptacle on the circuit, the receptacle itself must also be rated 20 amperes. If the laundry receptacle is a duplex receptacle or if the circuit contains more than one receptacle, it can be rated either 15 or 20 amperes.
210-21(b)(2) Total Cord-and-Plug-Connected Load
Where connected to a branch circuit supplying two or more receptacles (or outlets), a receptacle must not supply a total cord-and-plug-connected load in excess of the maximum specified in Table 210-21(b)(2).
This table shows the branch-circuit rating, the receptacle rating, and the maximum load permitted. This table does not apply to a single receptacle on an individual branch circuit—it covers branch circuits that supply two or more receptacles or outlets.
The maximum cord-and-plug-connected load on 15-ampere receptacles, supplied from either a 15- or 20-ampere branch circuit, is 12 amperes. Where 20-ampere receptacles are supplied from a 20-ampere branch circuit, the total cord-and-plug-connected load must not exceed 16 amperes.
The maximum load on 30-ampere receptacles, where connected to a 30-ampere branch circuit supplying two or more receptacles (or outlets), is 24 amperes. Notice that the maximum loads are a direct result of multiplying the receptacle’s rating by 80 percent.
210-21(b)(3) Receptacle Ratings
Where connected to a branch circuit supplying two or more receptacles (or outlets), receptacle ratings must correspond with the values listed in Table 210-21(b)(3). Specific receptacle ratings are stipulated for branch circuits that are rated 15, 20, 30, 40, and 50 amperes. A 15-ampere branch circuit can supply 15-ampere receptacles, but not 20-ampere receptacles. A 20-ampere circuit can supply either 15- or 20-ampere receptacles.
Receptacles fed from a 30-ampere branch circuit, must be rated 30 amperes. A 40-ampere branch circuit can supply either 40- or 50-ampere receptacles. While a 50-ampere branch circuit can supply 50-ampere receptacles, it cannot supply 40-ampere receptacles. For branch circuits that are larger than 50 amperes, the receptacle rating must not be less than the rating of the branch circuit.
210-23 Permissible Loads
The load on a branch circuit can never be higher than the ampere rating of that circuit. This is understandable, since a load with a rating higher than the rating of the overcurrent protective device will open the circuit. An individual branch circuit can supply any load for which the circuit is rated.
The rating of the load can be up to, but not exceed, 100 percent of the ampere rating on an individual branch circuit. A branch circuit supplying two (or more) receptacles or outlets must comply with 210-23(a) through (d), and also with Table 210-24. Permissible loads for 15- and 20-ampere branch circuits are covered in 210-23(a).
While 30-ampere branch circuits are covered in 210-23(b), 40- and 50-ampere branch circuits are covered in 210-23(c). Section 210-23(d) simply states that branch circuits larger than 50 amperes cannot supply lighting outlet loads. This requirement does not apply to cord-and-plug-connected arc welders.
210-23(a) 15- and 20-Ampere Branch Circuits
A 15- or 20-ampere branch circuit can supply lighting units, other utilization equipment, or a combination of both. The rating of any one cord-and-plug-connected piece of utilization equipment must not exceed 80 percent of the branch-circuit ampere rating.
A single piece of equipment that is cord-and-plug connected to a receptacle, can have an ampere rating up to 80 percent of the branch circuit’s ampere rating. For example, a copier is plugged into a 20-ampere receptacle that is supplied from a dedicated branch circuit.
If supplied by a 20-ampere branch circuit, the rating of the copier cannot exceed 16 amperes (20 x 80 percent). (See Figure 5.) If supplied by a 15-ampere circuit, the copier cannot exceed 12 amperes (15 x 80 percent).
The total rating of utilization equipment fastened in place, other than luminaires (lighting fixtures), must 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. [210-23(a)]
For example, a window air conditioner is plugged into a receptacle supplied by a 20-ampere, general-purpose branch circuit. The circuit feeding the air-conditioner receptacle outlet also feeds other receptacles. Other utilization equipment not fastened in place will be plugged into the other receptacles.
Because this fastened-in-place equipment is on a circuit with other equipment that is not fastened in place, the air conditioner must not exceed 10 amperes (20 x 50 percent).
If supplied by a 15-ampere circuit, the air conditioner could not exceed 7.5 amperes (15 x 50 percent). If the air conditioner was the only utilization equipment on the circuit, it could be rated up to 80 percent of the branch circuit ampere rating. Provisions for room air conditioners can also be found in Article 440, Part G (Part VII in the 2002 NEC.)
210-24 Branch Circuit Requirements—Summary
The requirements for circuits having two or more outlets (or receptacles), other than receptacle circuits of 210-11(c)(1) and (2) are summarized in Table 210-24.
This table provides circuit ratings for 15-, 20-, 30-, 40-, and 50-ampere branch circuits.
MILLER, owner of Lighthouse Educational Services, teaches custom-tailored classes and conducts seminars covering various aspects of the electrical industry. He is the author of Illustrated Guide to the National Electrical Code. For more information, visit his Web site at www.charlesRmiller.com. He can be reached by telephone at (615) 333-3336, or via e-mail at [email protected].