Hi guys, long time no post ("darn, he's back" I hear some say!).
Let me tell you of a fault I investigated recently; The gen AND panel had N-E bonds. The circulating currents throughout the installation were enormous! (the main current carrying conductors could carry up to 1000A each).
The solution was a single N-E bond in the panel and all Neutral and Earths met at this point.
However, the gen can also run in "augment" mode (supply the national grid with extra juice to stop the voltage & frequency falling too low) but this causes high Neutral currents (harmonics etc.). So in this mode the Neutral to the gen must be switched so as to stop high Neutral currents in the gen.
However, this raises another nasty. If you have a Neutral switch fault (open circuit) while in back-up supply mode, then the voltages that can appear L-N throughout the phases could be anything from subdued to almost 400V (taking 230V norm), and there situations where all three phases can suffer high voltages in this mode (I'm not going to go into that explanation now).
Does this make sense?
M.
