A: Several of our PESDs will allow an Insulation Resistance (Megger) Test to be performed and pass as expected. Devices that only have Test Point circuitry without LED Indication, such as the R-3MT, R-3MT-1K, and R-3MT-3K, will allow a successful Insulation Resistance test to be completed as long as reasonable levels of Insulation Resistance is desired, per the general rule of thumb of 1MΩ per 1000V of system Voltage.
While all of our PESD's are designed to handle voltage spikes associated with insulation resistance testing, the test will consistently indicate a failure when a PESD that has LED Indication is connected. Example Part Numbers include the R-3W Series, R-3MT-VI (ChekVolt), R-3F2, and R-3D2 parts.
This occurs because our PESD's internal circuitry provides a high impedance connection path to ground. The Ground (GND) LED circuit requires a path between ground and one or more phases to illuminate with ground faults and display a single phase condition. This is a small current path, in the microamp range allows for safe operation during normal operating conditions but causes the Insulation Resistance Test to fail. Please see the Ground LED Note and How Does the Voltage Indicator Circuit Work articles for more information on the function of the LED circuit.
To perform accurate insulation resistance testing on a PESD that has LED Indication, we recommend temporarily disconnecting the PESD's ground wire prior to the test. Once testing is complete, the ground wire should be reconnected for normal operation.