The power in the junction box or outlet box may be accidentally switched on and off by an unauthorized person.
A short circuit can occur when a wire slips off of an electrical device, such as an outlet. When it touches another wire, a short circuit ensues.
It's a common problem. A hot wire and neutral wire accidentally touch, causing a fire or electrical shock. This is sometimes referred to as an "accidental failure of an appliance".
Insects, rodents and other animals may chew the wire insulation and cause a short circuit between two wires within a cable bundle. This can cause electric shock or fire hazard to the customers. They must be identified, removed and replaced at all costs.