VERY SIMPLE and cheap......480 Volt. Use 6 240 volt light bulbs. 2 each in series off each leg. Simple as that. That is what we have on our 480 volt MCC"s. When you have a ground, 1 pair of lights will go dark and the other 4 will brighten up. It is then important to go looking for the ground fault cause if you get another on a different leg you will have a phase to phase short.
Dave