PV System Installation, Safety, and Maintenance
Domain 4 tests whether you can install, commission, and maintain a PV system without creating electrical or fall hazards. It rewards practical sequences: isolate, verify, work, reconnect, test, and document.
Electrical safety first
PV modules produce voltage whenever they are illuminated, so a "dead" array is not dead at the module terminals. Treat all DC conductors as energized. Use a lockout/tagout procedure, open and verify disconnects, and test with a meter rated for the system voltage before touching conductors. DC arcs do not self-extinguish as AC arcs do at a current zero, so DC disconnects and connectors must be opened under the right conditions. Wear appropriate PPE, including arc-rated clothing where required, insulated gloves, and eye protection.
Installation quality
Follow the manufacturer's torque values and connector system; mixed-brand MC4-style connectors are a common failure and warranty issue. Support and secure conductors, protect them from abrasion, and keep them out of standing water. Bond exposed metal, complete equipment grounding, and install rapid shutdown and labeling where the code requires them. Plan fall protection, ladder placement, and roof access before materials go up.
Commissioning and maintenance
Commissioning includes visual inspection, polarity and open-circuit voltage checks, insulation resistance testing where specified, inverter start-up, and monitoring setup. Maintenance is mostly inspection: look for cracked glass, discolored cells, loose connectors, corrosion, rodent damage, vegetation shading, and changed roof conditions. Compare strings under similar irradiance; a low-current string points to soiling, shading, or a failed module, while a missing voltage segment suggests a bypassed or disconnected module.
Worked example
A 10-module string should read about 400 V open circuit at 40 V per module. It reads 360 V on a clear day, and the inverter reports low input. The 40 V difference matches one module's Voc, so suspect a module that is bypassed, disconnected, or has failed. Isolate, verify zero energy, inspect each connector and module, and compare with the other strings before replacing parts.
Traps
Never assume the DC side is safe because the AC disconnect is off. Do not disconnect DC connectors under load. Do not clean modules with abrasive tools or while standing on them; follow the manufacturer's method.