In conduit I'm pulling several ckts. can I pull just one ground and how do I size it ??
And beyond that don't forget that if the current carrying conductors of a determining circuit set are increased in size for purposes of reducing voltage drop, etc., then the EGC must be increased in size proportionally.You can use a single wire type equipment grounding conductor for multiple circuits in the same raceway, it should be sized per T250.122 for the largest overcurrent device protecting conductors in the raceway. See 250.122(C).
Is it? Often it is it a waste of time, materials, and money.Depending on the conduit type and the distance you may not need an EGC.
But installing one is always a great idea.
Metal structure, multiple conduits, tons of parallel paths; even if there is a loose connector a fault clears with no problem.