From: peter2@hipson.net   
      
   On Tue, 09 Mar 2010 14:02:20 +0000, Tim Watts  wrote:   
      
   >PeterD    
   >  wibbled on Tuesday 09 March 2010 13:14   
   >   
   >> On Tue, 09 Mar 2010 06:55:17 +0000, Tim Watts  wrote:   
   >>   
   >>>Jon    
   >>>  wibbled on Tuesday 09 March 2010 06:41   
   >>>   
   >>>> All I need is a dpdt knife switch.  If I was cheap I'd get some copper   
   >>>> and make one myself.   
   >>>>   
   >>>> I just bought an economical manual dpdt transfer switch rated for 100a   
   >>>> at   
   >>>> 240vac.  I might have to have the electric company disconnect service so   
   >>>> I can wire it in.   
   >>>>   
   >>>> Don't tell me now I did something wrong.  What?   
   >>>>   
   >>>   
   >>>Don't you need 3p (two lives and a neutral)?   
   >>   
   >> Never switch neutral.   
   >>   
   >>>   
   >>>Have you found out how you need to handle the ground/earth connection?   
   >>>Here, in the event of a power failure,   
   >>   
   >> See above...   
   >>   
   >>>the utility earth cannot be trusted,   
   >>   
   >> You're required to have ground on your premises at the entrypoint.   
   >> Typically three ground rods.   
   >>   
   >>>so for   
   >>>a generator hookup, one needs a local earth rod or rods bonded to the   
   >>>neutral of the generator.   
   >>   
   >> Not just generator, but all service. And that's why you never switch   
   >> neutral.   
   >>   
   >>>As the earth loop fault impedance is now too high   
   >>>(typically 100+ Ohms for earth rod impedance) to trip a type B or C   
   >>>breaker in a timely manner, an RCD (you call them GFCI I think) must also   
   >>>be employed). What does your code say?   
   >>   
   >> (Comments based on USA rules, may vary in other countries!)   
   >   
   >That is interesting. Under the IEE Regs (UK), the neutral is considered a   
   >live (ie dangerous). To distinguish what most people think of as a "live",   
   >the other supply conductor is termed "phase", or more recently "line".   
   >   
      
   Well, we had a nice day today... I went out and did some scouting to   
   see how it is *really* wired (vs what the books say) and at each pole   
   where there is a transformer, there is also a ground rod (or rods)   
   that ground the neutral conductor at that pole. The neutrals are also   
   bonded between poles, too, with an overhead ground, so that they are   
   all connected together (this prevents problems if one pole's neutral   
   to ground rod or wire is damaged). This is likely quite different from   
   your setup in the UK, however.   
      
   >Thus, we are required to switch out the neutral in the OP's scenario, which   
   >is pertinent, as with certain types of supply fault on our 3 phase system,   
   >the neutral can potentially move up to 240V away from earth (and lead to a   
   >local 1 phase outlet experiencing a large voltage between the live and   
   >neutral, eg >300V - a scenario I have witnessed).   
      
   In the US, if your neutral ever rises above ground, there is a fault   
   and that fault must be corrected. Again, a difference in systems.   
      
   Code (again USA) specifically says: "do not switch neutral."   
      
   >...   
      
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