Question: Stranded conductors on receptacles and switches
I was always told that you could not use stranded conductors on receptacles and switches without crimping a spade terminal onto the stranded conductor and then securing the spade terminal onto the device screw terminals. Are receptacles and switches Listed for use with stranded conductors? Are they Listed for use with spade terminals?
UL Listed receptacles are evaluated for use with solid and stranded conductors; however, they are not Listed for use with spade terminals. Receptacles are Listed under the product category Receptacles for Plugs and Attachment Plugs (RTRT) located on page 295 in the 2008 UL White Book and (RTRT7) on page 434 in the 2008 Canadian White Book. The Guide Information for (RTRT) and (RTRT7) states under the heading of Terminals, “Terminals of the wire-binding screw, setscrew, or screw-actuated back wired clamping types are suitable for use with both solid and stranded building wires. Screwless terminal connectors of the conductor push-in type (also known as “pushin-terminals”) are restricted to 15 A branch circuits and are for connection with 14 AWG solid copper wire only.” They are not intended for use with aluminum or copperclad aluminum wire, 14 AWG stranded copper wire, or 12 AWG solid or stranded copper wire.
General use switches are Listed for use with only solid conductors unless otherwise indicated in their installation instructions. UL Lists general use switches for mounting in device boxes under the category of Switches, Flush (WMUZ), which falls under the main
category and Guide Information of General Use Snap Switches (WJQR), located on pages 348 and 347 respectively in the 2008 UL White Book. Their Canadian counterparts (WJQR7) and (WMUZ7) are located on pages 497 and 498 of the 2008 Canadian White Book.
The Guide Information for (WJQR) and (WJQR7) is silent on the solid and stranded issue in the 2008 White Books, however, the Guide Information for those categories will be clarified in the 2009 White Books.
Neither receptacles nor switches are evaluated for terminating a spade terminal under any of the terminals on these types of wiring devices. While this may be a common practice in the electrical trade when using stranded conductors, this would be a violation of NEC 110.3(B) as these wiring devices are not Listed for that application.
The Guide Information for the product categories discussed above can also be accessed on UL’s Online Certification Directory at www.ul.com/database and by entering the four or five digit category code in the Category Code search field.