Insulation resistance testing

Insulation resistance testing measures the resistance between the live parts of a PV array, its cables or a module and earth or the module frame. It is the only reliable way to confirm an insulation failure, because poor insulation often cannot be seen. Before testing, isolate the array from the inverter, keep unauthorised people away and disconnect surge protection devices or other equipment that could affect the reading or be damaged. Then connect the tester between earth and the array cables or combiner bus bar. The test voltage and the minimum acceptable resistance depend on the system voltage and are listed in the standard tables. Readings are taken in megaohms, and each circuit must meet its minimum value. Use this method to confirm cable defects, connector defects, glass breakage and junction box failure. Each of these faults can cause an insulation fault that may make the inverter trip or shut down the plant. If a dry test gives doubtful results, or you suspect installation or manufacturing defects, a wet insulation test can help find the fault. It simulates rain or dew and is good at exposing damaged wiring, poorly closed or cracked junction boxes, backsheet punctures and indoor-rated connectors. Faults may only show up when the array is humid, for example after rain or in early-morning dew. A dry test alone can therefore miss them. PV circuits stay live in daylight, so there is a shock hazard during the test. Wear protective equipment, make sure nobody touches metal surfaces, module backs or terminals, use a tester that discharges itself automatically, and confirm the system is de-energised before removing the leads.

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• sentence 1: support check: partial - Passages say bad insulation is not always visible and unequivocal detection is only possible by insulation resistance measurement, but the definition of measuring between live parts of array/cables/module and earth/frame is only loosely given (test between earth and array cables).
• sentence 3: support check: partial - Passages give test voltage tables for arrays up to 10 kWp (dependent on system voltage) and mention megaohm readings and Table 1, but do not state that each circuit must meet minimum in general beyond the ≤10 kWp case, and the larger-array table is not shown.
• sentence 4: support check: partial - Passages show these four faults can cause insulation faults and list insulation testing as a detection method, but the claim that each can trip the inverter or shut down the plant is only stated explicitly for glass breakage (plant stop) and cables (inverter failure); connector and junction box inverter trips aren't stated, and the dry-test method is not 'confirm'.
• sentence 6: support check: partial - Passages say faults can show after rain or in early-morning dew and that humid/wet measurement is better, but do not explicitly say a dry test can miss them (cables passage says detection possible under dry or wet; module says wet is 'better'). -->