In the test of the insulation layer resistance of photovoltaic cables, the insulation resistance value at a certain moment cannot fully reflect the insulation performance of a test product. This is because, on the one hand, the insulation material with the same performance has a small insulation resistance when the volume is large, and a large insulation resistance when the volume is small. On the other hand, the insulation material has an absorption ratio process and a polarization process for the charge after the high voltage is applied. Therefore, the power system requires that the absorption ratio - that is, the ratio of R60s and R15s, and the polarization index - that is, the ratio of R10min and R1min should be measured in the insulation test of many occasions such as the main transformer, cable, and motor, and the insulation condition is judged by this data.

Then, for personal safety and normal testing, the insulation layer resistance test of photovoltaic cables is not allowed to measure the charged test product in principle. Although measuring a charged test product will not cause damage to the instrument (in a short time), the test result is inaccurate, because after being charged, the test product is connected with other test products, so the result obtained cannot truly reflect the actual data, but the parallel or series resistance value with other test products.