[An older Control.com thread states:] "A power supply is considered to be floating if no part of the output of the power supply is connected to earth ground."

what does this mean .. and why do we need to do it?

 

Hello,

While I am not an EE or anything near it, from what I recall one of the reasons would be to allow for ground fault monitoring. Another would be isolation.

And the first question: It means the difference of potential is between the two outputs of the power supply rather than one output of the power supply and earth ground.

Cheers,
Mark
http://www.hmisys.com

 

Normally automation equipments like PLCs,SCADA system is being provided this type of supply.here POwer is being provided by means of POwer suppllies, whose neutral is not grounded. Because fault current in the earthing in case of fault can cause failure of Instruments.