XPost: sci.electronics.design   
   From: ehsjr@nospamverizon.net   
      
   Jon wrote:   
   > I'm trying to wire a transfer circuit for a generator.   
   >   
   > The generator will be located in the barn.  The electrical service is at   
   > the house.  Two 120vac wires and a ground go to the barn.  There is   
   > *one* unused wire from the house to the barn I can use for a signal   
   > circuit.   
   >   
   > When the power goes off at the house, I need to disconnect the service   
   > to prevent backfeed and activate for generator power to both the house   
   > and the barn.  When the service power goes on I need to disconnect the   
   > generator to avoid damaging it and restore normal service to the house   
   > and the barn.   
   >   
   > I have,   
   >   
   > *one 240vac 60 amp dpdt mercury relay   
   > *two 120vac 60 amp 3pdt relays.   
   >   
   > Any ideas?   
   >   
   > Jon Giffen   
      
   It's a no-go from the start.  The electrical code requires you   
   to use a listed transfer switch.  It *may* also prohibit you   
   from doing it yourself, even if you use listed equipment, and   
   require that the work be preformed by a licensed electrician.   
   Next, you need some large gauge wire from the generator to   
   the existing service if you will supply > 20 amps from the   
   generator.  You need to do a voltage drop calculation based   
   on how much current you will allow to be drawn and the   
   distance the wire must run, to verify that you are using   
   large enough wire.  Next, the code won't allow you to use   
   the same wires, regardless of transfer switches, for both   
   branch circuit wiring and feeder wiring.   
      
   What can you do yourself?  Dig the trench, plan the system,   
   check the codes, make sure the licensed electrician (if   
   you use one) agrees with all that is to be done and who   
   is to do it, lay the wire between the buildings.  Start   
   by making a *complete* list of *every* electrical device,   
   receptacle, appliance etc that is permanantly connected to   
   your wiring and identify which fuse/breaker controls   
   which circuit.  Then figure out the absolute minimum that   
   you intend to run from the generator, and "layers" beyond   
   that.  The "layers" could be something like: "minimum",   
   "convenient", "nice to have" and "full service".  The more   
   you want, the more it'll cost.   
      
   If money is no object, the simplest is to hire a pro and   
   specify complete backup, automatic transfer and let him/her   
   specify the equipment.  Unless you have a huge wallet,   
   that's probably a non-starter, too.   
      
   Ed   
      
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