using isolator to cut power

[corkie]

hi i would appreciate it if anyone can give me some good reasons why using the isolator to cut the power to a induction motor is not good practice.

i know it might be a stupid Q but i need to give 5 reasons for a college theory assignment. i know about the arcing and the contact's liable to weld together but i would appreciate a few ideas please

thanks in advance

[RalphChristie]

Not designed to break high currents.

 

Not rated for breaking currents.

 

Reducing life of isolator switch when breaking high currents.

 

Not very safe - can flash in your face during breaking high currents.

 

Breaking time slow in comparison with contactors.

 

On bigger motors the dielectric medium of an isolator switch is air, while the medium of the contactors are vacuum. Vacuum is a beter interupting-medium than air. (flashing)

 

On longer term - higher cost for maintance on the isolator switch.

 

Bad practice.

 

Regards

Ralph