To provide a technique for preventing water leakage due to deterioration of portions where water proof treatment of mounting fittings is not sufficient and saddles and machine screw for fixing are frequently used at fixing positions of a wiring protective piping routed from a roof to a connection box, the portions possibly causing rainwater leakage by construction of a photovoltaic power generation system.

Rainwater leakage can be prevented by a manner of waterproof treatment. However, such a waterproof treatment may be required at several tens of positions in construction of a photovoltaic power generation system. Therefore, there is a risk of rainwater leakage caused by mechanically handled and insufficient waterproof treatment or forgetting to perform the waterproof treatment. In an inventive method, the piping is fixed on a roof by using stainless wires without machine screw driving and hole drilling.