What is the difference between electrical equipment & electrical device? Where we use both?

Devices are elements of the electrical system that either regulate or enable access to electricity (such as outlets, plugs, and panels) (switches, circuit breakers, meters). With specific adjectives, equipment can also refer to items like distribution switchgear or transformers, or it might refer to an end-user machine that uses electricity, such a vacuum cleaner or a pump.

Consequently, when you turn on the lights, you are utilising both an electrical device (the switch) and an electrical item (lighting fixture and lamp).

The speaker's context can have some influence on meaning, although NFPA 70, the NEC, defines both phrases.