Assuming circuits 1, 3 & 5 are different single-phase breakers on 3 phases & yoked together, yes, you can share the neutral (it's desireable to do so) and generally the IG. Either way is legal by code, but more of a design issue- you can share the neutral but not the IG and vice-versa.
Whether or not you want to share the IG between the equipment really depends on the equipment- if it's related equipment, it's probably OK (often desireable, especially with interconnected electronic equipment that define hi/lo communications signal from the shared IG and can really get messed up from ground loops), but sometimes equipment has specific requirements that dictate it gets a dedicated IG.
Last edited by SteveFehr; 02/13/08 07:46 AM.
