NEC 2008
210.21 Outlet Devices. Outlet devices shall have an ampere rating that is not less than the load to be served and shall comply with 210.21(A) and (B).
(B) Receptacles
(1) Single Receptacle on an Individual Branch Circuit. A single receptacle installed on an individual branch circuit shall have an ampere rating not less than that of the branch circuit.
Exception No. 1: A receptacle installed in accordance with 430.81(B).
Exception No. 2: A receptacle installed exclusively for the use of a cord-and-plug-connected arc welder shall be permitted to have an ampere rating not less than the minimum branch-circuit conductor ampacity determined by 630.11(A) for arc welders.
(2) Total Cord-and-Plug-Connected Load. Where connected to a branch circuit supplying two or more receptacles or outlets, a receptacle shall not supply a total cord and-plug-connected load in excess of the maximum specified in Table 210.21(B)(2).
(3) Receptacle Ratings. Where connected to a branch circuit supplying two or more receptacles or outlets, receptacle ratings shall conform to the values listed in Table 210.21(B)(3), or where larger than 50 amperes, the receptacle rating shall not be less than the branch-circuit rating.
Exception No. 1: Receptacles for one or more cord-andplug-connected arc welders shall be permitted to have ampere ratings not less than the minimum branch-circuit conductor ampacity permitted by 630.11(A) or (B) as applicable for arc welders.
Exception No. 2: The ampere rating of a receptacle installed for electric discharge lighting shall be permitted to be based on 410.62(C)
(4) Range Receptacle Rating. The ampere rating of a range receptacle shall be permitted to be based on a single range demand load as specified in Table 220.55.
Om det är en enda behållare på en 20 Amp-krets måste den vara en 20 Amp-mottagare (bortsett från de 2 undantagen). Om det finns flera behållare på en 20 Amp-krets kan behållarna vara antingen 15 eller 20 Amp (bortsett från undantagen).
Det här gör att du kan ha flera enheter anslutna till att dra mindre än 15 Amps, men totaldragningen på kretsen kan vara större än 15 Amps.
Obs!
Tänk på att NEC definierar en behållare enligt följande.
Receptacle. A receptacle is a contact device installed at the outlet for the connection of an attachment plug. 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.
Således skulle en duplexbehållare betraktas som två behållare enligt denna definition. Vilket innebär att du kan installera en enda 15 Amp duplexbehållare på en 20 ampere krets utan att bryta mot den här koden.