The insulation resistance test is designed to detect very small breaks in the cable insulation before, during, and after installation. These breaks are often not detected during the continuity test because they are not necessarily short circuits between the conductor and the earthing braid. Even if small, these breaks can cause current leakage to earth. Such leakage is usually detected by the required earth leakage circuit breaker (thermostat with integrated earth leakage circuit breaker or panel-mounted earth leakage circuit breaker). When a current leakage is detected, the earth leakage circuit breaker breaks the circuit, thus deactivating the underfloor heating system. A megohmmeter (sometimes called a "megger") is a special type of ohmmeter that provides a high voltage to measure the electrical resistance of insulation. A regular ohmmeter or multimeter is unable to produce the required voltage and therefore cannot be used to perform this test.
The Model 6527 is a true multi-range handheld Megohmmeter® capable of measuring insulation resistance from 1kΩ to 4000MΩ. It features three user-selectable test voltages: 250V, 500V, and 1000V. The Model 6527 is also a multimeter with an AC/DC voltmeter function capable of measuring up to 600VAC and 1000VDC, a continuity test function with an audible signal for resistances less than 35Ω, and 600Vrms overload protection. In addition, it can measure resistance up to 400kΩ. The TEST button is combined with a lockout function for continuous testing of up to 15 minutes, eliminating the risk of overloading.
