PV System: how to ensure safety during maintenance or emergency

To ensure staff safety during maintenance and emergencies disconnect devices should be appropriately located and enclosures installation should be failsafe.

Isolation switching and control

• The switch disconnectors on the AC side and DC side of the inverter shall be installed for inverter service and maintenance.
• As many switch disconnectors should be installed as are needed to allow operation on the PV generator, particularly to replace fuses in the String combiner boxes and generator junction boxes.
• For PV systems inside buildings, a remotely-controlled switch disconnector should be mounted as closely as possible to the PV modules or to the point of entry of DC cables in the event of an emergency.

Fig. P14 – Switch disconnector Compact NSX 200A with heatsink and interphase barrier

Fig. P15 – Switch disconnector location

Note: Switches used in PV systems are designed to break the rated current of all poles at U_ocmax. To break the current when Uocmax is equal to 1000V, for instance, four poles in series (two poles in series for each polarity) are required. In double ground fault situations, the circuit breaker or switches must break the current at full voltage with only two poles in series. Such switchgear is not designed for that purpose and could sustain irremediable damage if used to break the current in a double ground fault situation. For this reason double ground faults must be avoided at all costs. Insulation monitoring devices or overcurrent protection in grounded system detect the first fault. Staff shall locate it and clear it without delay.

Selecting and installing enclosures

Enclosures for different PV generator boxes and switch boards on the DC side need to ensure double isolation, equipment protection against such outdoor hazards as temperatures, the rain, vandalism, and shock.

Enclosure and their auxiliary equipment must ensure temperature and humidity control to allow equipment to operate smoothly. It is, however, difficult to propose a generic solution. Each installation needs to be analysed in order to optimize the sizing of its enclosures and auxiliary equipment.