Oops, you miss read Don's reply. Go back and read it and you will find out that running the ground separately causes a high impedence grounding situation. This is a big problem during a fault condition and may cause the circuit breaker (or fuse) to not be able to clear the fault which would lead to a fire. When the ground is run in the same conduit this is not a problem.
A ground conductor that is dedicated to the equipment it serves or otherwise isolated from other loads it will not cause noise problems but will help clear them up.
Shane
