All DC components in a PV installation must be able to withstand a test voltage VP that is appreciably higher than the installation’s maximum open-circuit voltage VOCA. Moreover, modules, junction box housings and outdoor wiring must be resistant to sunlight (UV) as well as rain, snow, ice, high ambient temperatures behind poorly ventilated modules, and so on.
This minimum test voltage is as follows in accordance with the applicable national regulations (e. g. [4.4], [4.11], [4.12]):
where VOCA is the maximum open-circuit voltage for the entire PV system.
This in turn provides an allowable maximum operating voltage for the system:
In view of the elevated risk of arcing in PV plants, wherever possible protection class II components with double or reinforced insulation (protection class II insulation) should be used, whereby the following insulation requirements apply:
A surge voltage test (1.2 ps/50 ps) should also be conducted, as in Table 4.3.
This in turn provides an allowable maximum operating voltage for a system with protection class II insulation:
Although use of protection class II components with protection class II insulation does not reduce the risk of arcing, it does provide better protection against adventitious skin contact with the installation and thus enhances electrical safety.