RS485 bus: common ground wire needed or not?

[earckens]

Does a RS485 bus preferably have a common ground between connected devices?

Since a RS485 bus uses differential signals between two bus wires I would think not, but reading online comments on chip failures I now think otherwise. Correct?

EDIT: this is with a common power supply for all communicating devices.

 

[Nigel Goodwin]

If it's got a common power supply, doesn't that mean it's already got a common ground?.

 

[Diver300]

That transducer will work with several volts ground difference between transmitter and receiver. If there is no ground reference, mains pickup could easily give tens or hundreds of volts difference.

If the there is common power supply, there is no need for a separate earth, as Nigel says.

 

[earckens]

Ok, thanks for your fast replies!
Erik

 

[JimB]

If the there is common power supply, there is no need for a separate earth, as Nigel says.

Correct.

That transducer will work with several volts ground difference between transmitter and receiver.

Correct.
Look at the datasheet:

The input signals must be within the range -7 to +12v of the Ground (0V) voltage.

JimB