This chapter describes the ways of preventing mechanical damage caused by physical impact and the like. Mechanical damage to cable sheaths and metalwork of wiring systems can occur through corrosion, and hence care must be taken to choose corrosion-resistant materials and to avoid contact between dissimilar metals in damp situations. There are two ways of receiving an electric shock: by contact with intentionally live parts and by contact with conductive parts made live due to a fault. It is obvious that one may need to provide protection against both of these conditions. It will be evident that each of the protective devices provides a different level of protection, that is, rewirable fuses are slower to operate and less accurate than miniature circuit breakers. In order to classify these devices, it is important to have some means of knowing their circuit-breaking and 'fusing' performance.