Which of the flexible cables or cords listed below could be used to connect a piece of equipment that operates at 480 volts 3-ph?

The flexible cable option that would be suitable for connecting equipment operating at 480 volts in a 3-phase system is SEO. SEO cables are designed specifically to handle higher voltage applications, making them appropriate for industrial settings where equipment may operate under such conditions.

SEO cables are capable of carrying significant electrical loads and are rated for use in environments exposed to oil and moisture, which makes them ideal for heavy-duty applications in factories, construction sites, and similar environments where robust performance is crucial.

The other options, while they may be suitable for other applications, do not meet the specifications necessary for high voltages like 480 volts in 3-phase equipment. Therefore, SEO is the most fitting choice for such requirements.