What is the test for determining whether an occupier of a building is liable for damage caused to a plaintiff's property by an electrical shock?

To deal with the question of occupier's liability, it is conceded that the plaintiff was on the premises of the defendants as an invitee. This being the case, the test to be applied is that set out in Indermaur v. Dames (1866), L.R. 1 C.P. 274, wherein it is stated [at p. 288]: "The class to which the customer belongs includes persons … who go upon business which concerns the occupier, and upon his invitation, express or implied. "And, with respect to such a visitor at least, we consider it settled law, that he, using reasonable care on his part for his own safety, is entitled to expect that the occupier shall on his part use reasonable care to prevent damage from unusual danger, which he knows or ought to know; and that, where there is evidence of neglect, the question whether such reasonable care has been taken, by notice, lighting, guarding, or otherwise, and whether there was contributory negligence in the sufferer, must be determined by a jury as a matter of fact."