Practically Speaking: AL-CU Versus CO/ALR Markings

In 2023 and prior editions of the Code, I found it fairly easy to figure out if it would be a Code violation to terminate aluminum conductors directly on the terminals of the receptacle shown in the Photo below and others like it. But, for the 2026 Code, it is a little more difficult. In fact, it may not be Code compliant to do so.

Section 406.3(D)(1) in the 2023 Code stated, “Terminals of 15A and 20A receptacles not marked CO/ALR shall be used with copper and copper-clad aluminum conductors only.” But this marking did not apply to receptacles rated 30A and higher, such as the 30A receptacle in the photo. For a receptacle rated 30A and higher, the last sentence in Sec. 110.14(A) stated “Terminals for more than one conductor and terminals used to connect aluminum shall be 
so identified.”

This receptacle complies with Sec. 110.14(A). The same language is used for the 2026 Code. However, during the restructuring and reorganization of Art. 404 and 406 for the 2026 Code, some information may have been lost. For 2026, Art. 406 now applies to all wiring devices, including snap switches and receptacles. The device termination requirements in Sec. 406.10 apply to all wiring devices. Section 406.10(2) applies to all wiring devices not marked CO/ALR regardless of the amp rating of the wiring device and (a) states “They shall not be permitted to directly terminate aluminum conductors.”
Where does that leave installers when it comes to using aluminum conductors with receptacles like the one shown in the picture? Well, it certainly would not comply with

Sec. 406.10(2)(a) to terminate aluminum conductors on this receptacle even though it is designed and listed for the connection of aluminum conductors. It does still comply with Sec. 110.14(A). According to the product standard information for attachment plugs and receptacles, UL 498 (RTRT.Guidelnfo - Receptacles for Plugs and Attachment Plugs), “Terminals of receptacles rated 30A are intended for use with copper conductors only unless marked “AL-CU.” Terminals marked “AL-CU” are intended for use with aluminum, copper and copper-clad aluminum conductors. Personally, I would have no problem with terminating aluminum conductors on the receptacle in the photo, since it complies with product standards and Sec. 110.14(A). However, you may want to have a discussion with your AHJ about this, considering that it would not comply with Sec. 406.10(2). Unfortunately, the same type of conundrum happens with snap switches rated greater than 20A too. Perhaps this will all be clarified for 2029 or with a T.I.A. before that.