The only fire that I know about personally (neighbor down the street) was caused by a short circuit of some type in the wiring of a power outlet, in the little box in the wall. What they found is that the owner had done some re-wiring and added to the connections in the box, and hadn’t done it right. Anyway over time something had loosened, and eventually wires touched and fire started. Everyone got out, but that half of the house was pretty well destroyed. Insurance fixed everything, and they moved back in 4–5 months later.