Sometimes called “leakage resistance” the resistance measured between specified insulated portions of a temperature transducer when a specified DC voltage is applied. If insulation resistance should get very low, i.e., below 0.5 megohms, errors may result due to shunting of an RTD. A circuit in which any spark or thermal effect produced normally or in a specified fault condition is incapable, in test conditions prescribed NFPA Standard 493-1975, of causing ignition of a specified mixture of gas or vapor in air in its most easily ignited concentration.