XPost: alt.home.repair   
   From: andrew@cucumber.demon.co.uk   
      
   In article <529e37f2$0$46490$c3e8da3$a9097924@news.astraweb.com>,   
   	bud--  writes:   
   > The context is, specifically, in US power distribution is a split-phase   
   > supply called 2 phase with a phase A and phase B.   
   >   
   > (Not "2-phase", which as you say is rather different.)   
   >   
   > I don't think you have much split-phase over the pond.   
      
   No. 240/480V was only used on farms in very remote areas,   
   and there were probably no new installations of this type   
   since WWII (and there maybe none left by now, having all   
   been upgraded to 3-phase).   
      
   It's not necessary elsewhere here because we run 230V 3-phase   
   down each street, so houses which need more than 1 phase get   
   a 3-phase 230/400V supply. (In reality, it's 240/415V for   
   historical reasons.)   
      
   That doesn't work with the US 120/240V, because, to a first   
   approximation, you can only carry it a quarter of the distance   
   before the voltage regulation goes too bad (and the low power   
   pole mount transformers actually make this much worse).   
   This means you have to carry the high voltage supply down   
   each street and use regularly spaced pole transformers to   
   generate the 120/240V supplies. To keep costs down, there's   
   usually only 1 of the 3 phases from the HV supply carried   
   down each street, so you don't generally have access to a   
   3-phase supply in any one residential street.   
      
   > If I remember right, construction sites may have 120/60V circuits.   
      
   Construction sites here use a safety supply of 110V with   
   earthed centre-tap, i.e. 55-0-55 for single phase and 65/110V   
   for 3-phase, but the 0V connection is only grounded at the   
   transformer and carried to tools as a protective ground   
   conductor, and never used as a power conductor, so these   
   are never described as 55-0-55 or 65/110V supplies, because   
   there's no neutral connection. This is designed to prevent   
   electrocution of construction workers if a tool gets dropped   
   into a puddle or the cord is damaged or something similar,   
   as the highest voltage to ground is only 55 or 65V.   
      
   This safety supply used to be mandatory on UK construction   
   sites. It's no longer mandatory (that would be contrary to   
   EU rules on movement of workers and products), but it's what   
   you'll still find on all UK construction sites.   
      
   --   
   Andrew Gabriel   
   [email address is not usable -- followup in the newsgroup]   
      
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