Regeneration is a typical event with motors. All motors may turn into generators under the appropriate circumstance.
Read this app-note for more information. 

CLICK HERE 

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Multiple ground loops create the possibility of large unwanted currents in signal ground paths with possible damage. 
Read this app-note for more information.
 
CLICK HERE 

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Separating grounds in relay circuits is critical to be able to use them in different sections of a circuit.
Read this app-note for more information.

CLICK HERE

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Suppress arcing in relays to improve the life of the component.
Read this app-note for more information.

CLICK HERE