The common terminology I have heard in the US (don't have any standard handy) is that 460vac and 600vac are low voltage and all higher voltage motors are medium.
This would follow from the terminology used for distribution systems where the breakpoint between low and medium voltage is 1000vac. I don't remember the breakpoint between medium and high (30kvac?) and between high and EHV (200kvac?), but it's not very relevant for motors which even at 13.2kv, would still be medium voltage motor.
You probably know: for motors there clearly is some distinction in construction when stress control becomes is required which is somewhere around 6kvac depending on preferences.
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(2B)+(2B)' ?