Necdigest ?, February 2007
Compiled by Jeff Sargent and the NFPA Electrical Engineering Team
Q. Can I use 14-2 wire for the switch leg of a light fixture where the branch circuit is protected by a 20-amp circuit breaker? If this is against Code, why can I use 15-amp switches and receptacles on 20-ampere circuits?
A. The conductors from a switch location to the lighting outlet it controls are considered branch circuit conductors, not tap conductors connected to branch circuit conductors. These conductors are subject to the general overcurrent protection requirements of Section 210.20(B), which points to Section 240.4 for the specific overcurrent protection requirement. Section 240.4(D) specifies that 14 AWG copper conductors are to be protected by an overcurrent protective device with a rating or setting no higher than 15 amperes. And Table 210.24, which summarizes the requirements for branch circuits with two or more outlets or receptacles, specifies that the minimum conductor size for a 20-ampere-rated branch circuit is 12 AWG
Section 210.21(B)(3) permits a 15-ampere receptacle to be connected to a 20-ampere rated branch circuit. The terminals of feed-through type receptacles rated 15 amperes are tested for the heating that will result from the full load of a 20-ampere branch circuit. In addition, the attachment caps of cord-and-plug appliances are configured based on the appliance load. If the appliance is rated greater than 15 amperes, its cord cap will not be compatible with the configuration of a 15-ampere receptacle.
Snap switches installed on branch circuits are subject to the load requirements specified in Section 404.14. For AC general-use snap switches controlling resistive or inductive lighting loads, the minimum rating may not be less than the load it supplies. In other words, a 15-ampere switch installed on a 20-ampere circuit may supply a load of 15 amperes. For switches controlling lighting outlets supplied by 15- and 20-ampere branch circuits, it is the load controlled by the switch, not the rating of the branch circuit, that determines the switch?s minimum ampere rating.
