Got a call from the furniture store today. He said the hydro inspector was by and asked that he get ground detection lights installed for his 100A 600V service. Very rarely do I get asked to install this. I am aware that Delta 3ph systems require this and many of this type of system is still used in the older part of the city. Why do I need these lights on the Delta systems and never on the Wye? Any websites or insight on ground detection lights and how they work would be appreciated.