What must be true regarding receptacles according to the NEC standards?

According to the National Electrical Code (NEC) standards, receptacles must be listed and marked. This requirement ensures that the receptacles meet specific safety and performance standards established by recognized testing laboratories. A listed receptacle is one that has undergone testing and evaluation to ensure it conforms to industry safety standards, which helps prevent electrical hazards such as shocks, fires, or equipment damage.

Markings on receptacles serve to inform users about the rated voltage, current, and other specifications critical for safe usage. This standardization is essential for ensuring compatibility and safety in electrical installations. A receptacle that is not listed or marked could potentially lead to unsafe conditions and is not compliant with NEC regulations.

Other options suggest conditions that would not ensure safety or adherence to regulatory standards. Unmarked receptacles may lack critical safety information, standard size limitations ensure compatibility with plugs, and homemade receptacles would not be compliant with safety testing requirements.