Proper grounding of SPD modules and the main PE bus is essential to protect the system from transient overvoltages. Why Combiner Box Grounding Matters More Than You Think In solar installations, the photovoltaic. But did you remember that photovoltaic AC combiner box grounding could make or break your entire system's safety? In 2023 alone, improper grounding caused 23% of solar-related electrical fires according to NREL's latest report. If voltage to ground exists from either conductor, check each connection point (DC disconn ct, combiner box) all the way b reakers for Solar Panels. What is a solar combiner box? Solar.