Up to 12 V DC does not pose a safety hazard under normal conditions. In cases where a PV installation’s open-circuit voltage VOCA is less than 120 V and the installation is not connected to the low-voltage grid (~230 V), no further safety measures are necessary. However, in actual PV systems it is not always obvious for which conditions open-circuit voltage is to be determined. As most electrical data on vendor datasheets pertain to STC (1 kW/m2,25 °C), this readily accessible data should by all means be used. In a 12 V system such as the M55 with five series-connected monocrystalline or polycrystalline modules, 120 V will not be exceeded. Moreover, in systems installed in flat areas, STC conditions are almost never reached.
In the summer, when 1 kW/m2 insolation can occur from time to time, module temperatures far exceed 25 °C and thus open-circuit voltage is lower. And while module temperatures are lower in the winter, insolation is considerably below 1 kW/m2 at the usual tilt angles, which also leads to lower open-circuit voltage. Thus in cases where six such modules are wired in series in a flat area, protection class III conditions often obtain and 120 V is only slightly exceeded, and then only in rare cases.