What is the Difference between OLR (Over Load Relay) and MCB (Miniature Circuit Breaker) ?

• The OLR and MCB both are depends upon the current range.
• But why we are choosing both devices for single machine ?
• For Example : MCB have the 70 Amps (rated) 90 Amps (MCB) means at a time of 90 Amps only it will trip. But heat is increased and machine get damaged.
• But in OLR coil  strip will cut at a time of more heat. So, No need for current range.