Will Earth hour do damage to power supply system?

Strange voltage between line and earth?

• I got asked to help with this domestic job (yes I am a qualified electrician) but the values we are reading are very odd. It's an old house so only has one circuit each for power and lighting and when the power circuit is on and the lighting circuit is off there is 20v between line and earth and when the lighting is turned on there is 225v roughly between line and earth on the lighting circuit. Now the house passed insulation resistance, earth continuity etc all fine. I just am stuck as to how the earth can have 20v on it? After checking a few connections and re-terminating them the voltage dropped to only 14v. Is it possibly that the power circuit is inducing 14v into the lighting/earth system? As a side note the original job was to install 2 fans and change over a light and the RCD tripped about an hour after they were turned on. There is also some pretty obvious DIY that has been done (such as CAT3 used as a switch wire :s) but what has been found has been rectified. Any help or ideas would be appreciated.

• Answer:

  It appears that in 20vline phase is reversed.