Why is a 4kHz sampling rate commonly used for three-phase induction motor voltage RMS?

Why it is required to have a sampling rate of at least 4kHz when sampling the voltage waveform of a three phase induction motor.

I find most research papers use 4kHz but they don't state why.

I want to understand why 4kHz as appose to 5kHz or even 10kHz for example. I need this waveform to calculate the RMS.

Thanks in advance.