4.22.4.1 Polarity in Cord-and-Plug-Connected Appliances. If the appliance is provided with a manually operated, line-connected, singlepole switch for appliance on–off operation, an Edison-base lampholder, or a 15- or 20-ampere receptacle, the attachment plug shall be of the polarized or grounding type. A 2-wire, nonpolarized attachment plug shall be permitted to be used on a listed double-insulated shaver.
FPN: For polarity of Edison-base lampholders, see 4.10.7.9(a).