The potential source of harm in this case is electricity, or more precisely the effects of electricity. There are many techniques for evaluating risk that do not depend on the consequences being realised. Otherwise we would need a nuclear power plant to fail before we could evaluate the control systems used to prevent such failure.
That is true - but in such (relatively unusual) situations, one cannot 'evaluate risk' but, rather, has to make an
estimate of risk based on theoretical considerations.
In the case of hazards which result in incredibly rare risks of very serious consequences (as in nuclear power plants), one has no option but to adopt such an 'estimation' approach, non-ideal though it is.
Kind Regards, John