Jeff-hottub

All - I have a strange one. So I keep having the hot tub blows the Dual 60 amp non GFI breaker instantly inside the house, I do not have a GFI just a knife disconnect on the outside of the house.. If I disconnect the Black wire on the heater it works fine. As soon as I connect the black wire it trips. So thinking this is a easy fix. Ordered a new heater, Well that did not help. Now the board where the heater plugs in is burnt up with back everywhere. Board still works but not looking so good. I swapped out the 60 amp Dual Breaker in the house same issue. I tighten all the connections from the Panel to the tub. I am at a lost. I have a 2003 Sweetwater/Sundance Brita 240V spa with circ pump, Thanks Jeff