I have seen a lot of verbage regarding locating grounds on ungrounded systems.I do this all the time WITHOUT shuting down equipment. Where I work we can not randomly shutdown equipment.
What we have is what we call a thumper. It is a 480V strip heater in series with a pulsing contactor and an 10amp analog meter.
To locate a ground we first determine which phase is grounded. Then we hook the unit up to one of the ungrounded and the other side to a good ground.Then we turn on the thumper on. It will generate a pulse inversley proportional to the quality of the ground. The current is read on the ammeter. Now a thong ammeter with a 0-20 amp scale with a jaw that fits around 4" conduit is snaped around each conduit or cable ALL THREE WIRES AT A TIME until the pulse is located . Then we follow the pulse until it stops. That is the where the ground is. With this equipment we can locate most grounds in 30 minutes or less. Some of our newer switchgear has ground locating pulsers built in it.