3 Way (4 Switch) Insteon Setup for Ceiling Fan Light
I'm not getting a very good picture from your diagram. From what I can tell the switches aren't shown? Or maybe they are but the light isn't? Anyway here's what seems to be going on: The switch that blows the breaker could have a neutral or ground wire connected to the load side of the switch. When the switch contact is made you have a dead short. OR the wire that's supposed to be "hot" coming into the switch is actually a neutral or ground. To troubleshoot this I would use a volt meter. Turn off power. Remove load line from switch that blows breaker. Turn power on. If the breaker blows with the load line removed then the switch is bad. If it doesn't then connect one lead of voltmeter to ground (non insulated wire) and the other lead to the load side of switch. Turn the switch on and tell me the results.