Varistors with internal thermal protection are also available

While a MOV is designed to conduct significant 2SJ148 power for very short durations (?? 8/20 microseconds), such as caused by lightning strikes, it typically does not have the capacity to conduct sustained energy. Under normal utility voltage conditions, this is not a problem. However, certain types of faults on the utility power grid can result in sustained MIP144 over-voltage conditions. Examples include a loss of a neutral conductor or shorted lines on the high voltage system. Application of sustained over-voltage to a MOV can cause high dissipation, potentially resulting in the MOV device catching fire. The National Fire Protection EA1530A Association (NFPA) has documented many cases of catastrophic fires that have been caused by MOV devices in surge suppressors, and has issued bulletins on the issue.There are several issues to be noted regarding behavior of transient voltage surge suppressors (TVSS) incorporating M68702H under over-voltage conditions. Depending on the level of conducted current, dissipated heat may be insufficient to cause failure, but may degrade the MOV device and reduce its life expectancy. If MHW812A3 excessive current is conducted by a MOV, it may explode inside the case, keeping the load connected but now without any surge protection.