XPost: alt.engineering.electrical, sci.electronics.design   
   From: sylvia@not.here.invalid   
      
   On 9/08/2010 12:50 AM, Jon wrote:   
   > The electrical service goes to the house.  There are 3 underground 000   
   > cables that go to the barn from the house. The barn has a 60 amp breaker   
   > in the breaker box at the house. The 12,000 watt generator is in the   
   > barn. It has a 50 amp 240vac outlet, a 30 amp 240vac outlet and several   
   > others. I am hooking the 50 amp outlet to the house. I am using the same   
   > 3 underground 000 cables to send generator power to the house during a   
   > power outage.   
   >   
   > A 90 amp contactor in the barn won't connect the generator to the house   
   > unless:   
   > 1. The electrical service to the house is off, and   
   > 2. The service disconnect switch at the house is off.   
   >   
   > When the generator is turned on, it tests the service disconnect at the   
   > house to assure the above two conditions are met. This is done by   
   > sending a 1 second electrical pulse to the house to see if it will   
   > actuate a coil. If the coil actuates, the 90 amp contactor latches open   
   > and prevents backfeed into the grid. If the service power turns on   
   > during that 1 second, the generator power and service power will clash   
   > and throw a 50 amp breaker to the generator.   
   >   
   > http://jons-math.bravehost.com/transfer.html   
   >   
   >   
   >   
      
   I'd have thought the grid operator would want a cast-iron guarantee that   
   you won't backfeed the grid, lest you enliven wires that linesmen think   
   are dead.   
      
   What's wrong with a DPDT relay?   
      
   Sylvia.   
      
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