From: JERONI.PAUL@terra.es   
      
   Peter W. wrote:   
   > Once more, an observation from a US perspective.    
   >    
   > The basics: US residential systems are, typically 120/240 volt, single phase   
   systems with two "Hots", a neutral and a ground. Hot-to-Hot is 240 volts @ 60   
   HZ ac. Hot-to-Neutral is 120 Volts AC. Ideally, Neutral and Ground are at the   
   same potential, and,   
    again, typically, are bonded together in the main panel. The main panel is   
   also required to have a separate ground. The main service to the utility   
   transformer is three-wire, typically. Just the hots and the neutral.    
      
   Here in Spain most last mile distribution is 230/400V at 50Hz with four wires   
   running through the streets, one neutral and three hots (triphasic).   
   Hot-to-neutral is 230V and hot-to-hot 400V. Most homes are connected to only   
   one hot and neutral (230V    
   monophasic) and it is up to the electricity company to distribute homes   
   through their three hots to balance their systems. Inside home there is   
   nothing to balance. In residential areas triphasic is only used for older   
   single or dual speed lift motors and    
   heavy air conditioners.   
      
   In older areas there are still some 115/230V networks, for example where I   
   live. 115V was used maybe 50 years ago but it is very unlikely anyone is   
   connected to that anymore, if someone keeps such vintage appliance there are   
   plenity of 230-115    
   transformers available cheap second hand. In these areas two hots enter homes,   
   the neutral is not even connected at the street wires (when it is, it was for   
   115V and currently unused).   
      
   >    
   > Now, differential issues. One of the discovered weaknesses in US-code wiring   
   early on was the multiple-devices issue. Say, there are eight receptacles on a   
   single circuit, wired in parallel, of course. The last device in the chain is   
   after multiple    
   splices or connections. Each one adding some tiny amount of resistance. So,   
   there is some potential between the ground of the first device and the last.   
   If the original electrician was sloppy, that potential can be sufficient to   
   trip a ground-fault    
   device. And, the end-user will perceive this as a nuisance-trip, not a   
   problem. For the record, it is a problem and should be corrected. Not sure how   
   things are done in Europe, but if conditions are similar, look for this as   
   well.   
      
   I don't understand how that small voltage drop in the cabling causes an   
   imbalance in current. The earth in all appliances is supposed to be fully   
   isolated from the hot/neutral isn't it?   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)