I would draw the line in this circumstance, where the work done by a person in their own house, could affect the safety of other users on the same electricity network.
I know something like this is rather rare, but it has happened before.
Trumpy,
Can you elaborate on this? You've got me trying to imagine what kinds of domestic DIY wiring faults could cause problems further back in the system. Provided the main fuse is not bypassed or upgraded (is that where the problem is?), any overloads or short circuits will only affect the consumer side of the fuse. Mixing up earths and phases will again blow local fuses, whereas earths and neutrals mixed will have no effect on the supply as these should already be connected together at the neutral link.
Sure mate,
What is not clearly understood, even by electricians in this country (NZ), is that any bad connection in the MEN (Multiple-Earthed Neutral) system, can cause rising earth currents not only in your own installation, but on properties either side of you, that do have better connections to Earth.
Should there be an appreciable fault in your house, that cannot find a low enough impedance to operate a main fuse at a pole or pillar box, that fault current will continue through any low impedance paths (namely the neighbours N/E system) until sufficient current is obtained to trip the protection.
We are talking 1000's of amps here, not 100's of amps.
If however the person has done things right and installed Circuit Breakers,the circuit will trip in a shorter time, if they haven't and have merely "upgraded" an existing porcelain fuse circuit, it will take longer to blow that fuse.
In any installation, make sure your earth and neutral connections are well made and tight.
After all, there are MEN connections in houses that have not been checked or tightened in years, they will at the most carry 63A here, but, that does not take into account the ever climbing PSCC values of the outside electricity network.
