@ Dear Mr. RRaghunath (Electrical)8 Jun 22 06:21
"...#1. I think it is OK as you won't be switching the motor using the isolator. #2. AC3 rating is specifically about switching squirrel cage induction motor current and capability of the isolator to successfully interrupt"..
#1. Per IEC 60947-3, an (isolator=disconnector) AC20 [is intended for make/break without load/current]. The circuit shall have a breaker/load break switch at the up-stream. To (prevent any inadvertent operation by the operator), this isolator must interlocked to switch off the up-stream and labeled/forewarn the operators that it shall [not be used for on/off switching with load].
#2. Per IEC 60947-4-1, AC3 is utilization category for contactors. For switching devices, the utilization categories are AC20...AC23 . A AC23 would be capable of switching motors.
Che Kuan Yau (Singapore)