Recently I came across a 480V 3-wire delta service with one leg grounded. An associate at Edison told me that 480V corner ground systems are illegal but 240V ones are not. This is the first time I have seen a 480V corner ground. I could not find anything on the code for it. Article 100, definitions mentions 480V 3-wire open grounded systems. What should we do with this service? And why would a 480V corner ground be legal when a 240V is not?