Please See the drawing and Advise......
Overload - is just that - too much load on the motor, this is typically a long time ( relative to Short circuit issues) the OL Relay is configured for this case,, e.g. 150% of full load for 60 Seconds - etc.
A short circuit - is a fault, and the MCB is set up to protect for these cases, for example 5 to 10 x the Full load current, and this typically will trip in short ( 0.1 to 0.5 Sec after the Current is detected) or Instantaneous (as soon as the current is detected) -
The two device are protection for different types of problems.
Google Coordinated Motor Protection - that will probably be helpful.
ismat143 -- please check your PMs.
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