Andy,
Just a reply to your question that warrants an answer.
The house was fed with 3x 16mm2 Neutral-Screened from the pole in question.
Cable like this can be fused at 63A per phase, as a rule of thumb, that is the maximum current draw that N/Screened will handle buried direct.
What happened though, was the EC that installed the Service Line, ran the thing in 100mm Orange PVC Conduit (which personally I don't blame him for doing, considering it ran under several gardens on the way to the Main Switchboard) and through the concrete pad that the house was built upon.
Now having said that, any person that knows anything about Underground Cables, also knows that when you run a cable through Conduit, it has to be de-rated by a certain factor.
Length of run in this case gave a derating factor of 10% (0.90).
But the one thing that sets this incident apart from any other that I have seen is this:
- 3 fuses blow at 5 minute intervals,
Sure they were originally fused with 50M63 links(gM) - From what us Fire Officers can tell, the water pump was faulty, hence the humming Contactor.
Tests concluded that the Pressure switch was stuck shut, it had been like this for a week or more. - Also what we were not looking for, but found anyway, was the fact of the Underfloor heating system had a resistance of 100 ohm to Earth, we can't be sure, but it could have had something to do with the fire, considering evidence from a PoCo inspector saying that the Afternoon Boost was on at the time that the fire would have happened
