components and the breakdown of complete control units can severely interfere with a process technology procedure. The extent of surge damage caused by a lightning stroke often becomes apparent only some weeks later because more and more electronic components have to be replaced because they no longer operate safely. Such damage can have serious consequences for an operator using a so-called field bus system because all intelligent field bus components together in one segment can break down simultaneously. The situation can be improved by installing lightning and SPDs, which have to be chosen to suit the specific interface. Typical interfaces and the protective devices appropriate to the system can be found, e.g. at www.dehn.de.