Only the 331 and 332 were sold with a 15amp IEC socket. The 333 was sold with a captive power cord due to its ability to be used on a 15amp, 20amp or 30amp circuit. For compatibility with existing household outlets, a standard three prong, 15 ampere plug is provided on the 333s captive, high current AC mains cable. If you decide to use a dedicated, higher-current (30 ampere) line for your Nº 333, the only thing that needs to be changed is the AC plug itself.