Cautions and warnings Surge arresters must not be operated directly in power supply networks,whose maximum operating voltage exceeds the minimum spark-over voltage of the surge arresters. Surge arresters may become hot in case of longer periods of current stress (danger of burning). If the contacts of the surge arrester are defective, current stress can lead to the formation of sparks and lou Surge arresters may be used only within their specified values. In case of overload, the head contacts may fail or the component may be destroyed.  Damaged surge arresters must not be re-used.