Off-grid safety requirement
DC Protection
DC isolators, fuses, polarity checks and surge protection.
Off-grid PV strings and battery circuits carry DC power. DC protection must use DC-rated devices and correct cable/fuse sizing so faults can be isolated safely.
Why It Matters
DC faults can be harder to interrupt than normal AC faults.
Correct isolation makes maintenance and emergency shutdown safer.
Surge protection helps protect controllers, inverters and monitoring devices.
Required Checks
PV string voltage and current under expected temperature conditions.
DC-rated isolator, fuse, MCB and SPD selection.
Positive/negative polarity and cable color/label consistency.
Cable size, gland sealing and enclosure IP rating.
SPD earth connection and DB labeling.
Required Documents
DC single-line diagram.
DCDB protection schedule.
Fuse, isolator and SPD datasheets.
Cable sizing record.
Commissioning checklist with polarity and voltage readings.
Installation Details
Use DC-rated switchgear on the DC side.
Keep DC cable routes protected from heat, water and physical damage.
Label PV input, battery input and shutdown sequence clearly.
Confirm open-circuit voltage before connecting controller/inverter.
Handover Records
Final SLD.
Protection device ratings.
DB photos and labels.
Shutdown and isolation procedure.
Service Notes
Inspect DBs for heat marks, loose terminals and water entry.
Replace SPD if failure indication is visible.
Do not bypass fuses or isolators during troubleshooting.