Personal injury - Damage by over-passing electrical wires - Claimant working on un-approved building extension - Whether owner of vacant house ' occupier' - Principle of causation examined - proximate cause of injury - Whether Volenti decence available to defendant - Whether opinion evidence of non-expert of relevance - Non-delegable duty of care of independent contractor for inherently dangerous work - Proof of negligence when standards set by JBS nont contravened.