Electrical Safety, Tools and Work Practices
Electrical hazards
Electrical Safety, Tools and Work Practices covers the hazards that make solar work different from ordinary AC work. PV arrays produce dangerous DC voltage whenever light falls on them; there is no 'off' switch at the module. DC arcs do not self-extinguish as easily as AC arcs. Battery banks can deliver very high short-circuit current, and lead-acid batteries produce hydrogen and acid. Work at height adds fall and dropped-tool risks.
Safe practice
Use lockout/tagout for inverters and AC isolators, but remember the DC side remains live. Wear insulated gloves, eye protection and arc-rated clothing where required. Use insulated tools and a meter with a suitable CAT rating. Discharge and prove dead before touching conductors. Work with a second person, ventilate battery rooms and keep a first-aid kit and fire extinguisher suitable for electrical fires.
Worked example
A string has 20 modules, each with Voc 40 V. At open circuit the string is about 800 V DC. A meter rated CAT II 600 V is not suitable. Use a CAT III 1000 V meter and insulated probes. Even after the inverter is isolated, the string cable remains live until the array is covered or the string is disconnected at both ends.
Traps
Do not assume a 'dead' inverter means the array is safe. Do not short a battery to test it. Do not use a damaged test lead or a meter with a cracked case. Do not work alone on a roof or in a battery room.