XPost: alt.home.repair   
   From: andrew@cucumber.demon.co.uk   
      
   In article <529f9729$0$46054$c3e8da3$88b277c5@news.astraweb.com>,   
   	bud--  writes:   
   > On 12/3/2013 4:36 PM, Andrew Gabriel wrote:   
   >> 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.)   
   >>>   
   >>> 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.   
   >   
   > It is what I attempted to convey it too few words.   
   >   
   > If I remember right, there are bathroom outlets that are connected the same.   
      
   Rules for bathroom sockets in the UK are that it must be from   
   an isolating transformer, and restricted to (IIRC) 25W (usually   
   restricted by a very slow acting self reset thermal fuse, or   
   just a self-reset thermal switch on the isolating transformer).   
   It's intended for shavers, electric toothbrushes, etc.   
   The isolating transformer is to prevent risk of electrocution   
   in an environment which is likely to be wet, and the person   
   and appliance is also likely to be wet. The output is   
   isolated and not connected to ground (which would defeat the   
   whole object).   
      
   There's always a 120V socket and a 240V socket, simply because   
   if you have an isolating transformer there anyway, the cost of   
   providing an extra voltage output is negligable.   
      
   This rule has been relaxed in the latest regs to allow ordinary   
   socket outlets providing they are at least 3 meters from a   
   bath or shower (IIRC - haven't got the regs to hand just now).   
   This allows for having a shower in a bedroom, for example,   
   and having standard sockets in the rest of the bedroom.   
      
   >> 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.   
   >   
   > How does the EU get involved.   
      
   EU has rules requiring that all member states allow free movement   
   of people and products across borders. This prevents the UK from   
   insisting that construction site tools must all operate on a   
   special voltage only found in the UK, as a carpenter from, say,   
   Italy won't have 110V tools, and thus would not be able to take   
   up a job on a UK construction site.   
      
   In practice all UK construction sites are still 110V and all UK   
   construction workers tools are 110V, but in theory an Italian   
   carpenter could now turn up on site and request a 230V supply   
   for his tools - that used to be illegal. At one point in the   
   negotiation of this change, 110V construction site tools were   
   to have become illegal in the UK - they were only saved because   
   they result in far fewer construction site electrocutions than   
   is the case in other EU countries which use 230V tools.   
      
   --   
   Andrew Gabriel   
   [email address is not usable -- followup in the newsgroup]   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)