From: peterwieck33@gmail.com   
      
   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. However   
   the Utility transformer    
   is grounded as well. As our house has a copper water service to the street,   
   the main panel is also tied to the water service, and the water meter is   
   bonded (ground wire bridging the water meter) which grounds the copper   
   plumbing throughout the house. We    
   have an hydronic heating system (black iron) and a gas stove and dryer - also   
   fed with black iron. Both those systems are bonded to the copper plumbing.   
   Meaning pretty much all the piping in the house is grounded, but for a few   
   peripheral odds and ends    
   that are fed in PEX due to upgrades and/or repairs over the years.    
      
   The first thing I did when we moved in was "balance" the panel. This with a   
   clamp-on ammeter. So, under most conditions, there is no asymmetrical loading.   
   240  Volt loads are always balanced.   What this means is that if we get   
   repeat trips on a ground-   
   fault breaker, we know we have a problem to be checked and corrected before   
   reapplying power. We also know that any 'leak' into the plumbing will go   
   directly to ground.    
      
   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.   
      
   Peter Wieck   
   Melrose Park, PA   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)