In order to ensure that the DC side can be shut down while under load, a DC-compatible load switchgear device should always be used whose rated direct current is higher than the maximum rated solar generator short-circuit current and whose rated DC voltage is higher than the system’s maximum open-circuit voltage VOCA for the solar generator. String fuses should be changed or circuit breakers opened only when this isolating switch has been opened. This switch is often accommodated in the generator junction box. For larger installations (e. g. those comprising a number of arrays) an additional DC switch should be installed near the charge controller or inverter.
188.8.131.52.4 Overload Protection
As all solar generators are mounted outdoors, they are exposed to lightning-current-induced power surges. To protect the modules and wiring against such surges, the clearance between (a) module areas that are electrified by the module wiring and (b) lighting rods and down-conductors should be as small as possible. Moreover, suitable surge diverters (varistors, if possible either sufficiently oversized or equipped with thermal monitoring devices for ageing induced leakage current increases) should be integrated into the solar generator junction boxes (in relatively close proximity to the modules) between the positive and negative conductor and ground. For further information concerning lightning and power surge protection for PV plants, see Chapter 6.