Electrical Installation and Wiring: DC/AC Cabling, MC4, Combiner Boxes, Earthing and Surge Protection
This section covers electrical installation and wiring: DC and AC cabling, MC4 connectors, junction and combiner boxes, earthing, lightning and surge protection, and cable routing. The exam tests safe, code-compliant workmanship on the DC side, where faults are harder to extinguish.
DC cabling and connectors
Use double-insulated, UV-resistant PV cable of the correct cross-section. Keep polarity consistent, label strings, and crimp MC4 contacts with the matching tool; pull-test each connection. Never mate or unmate MC4 under load. Combiner boxes group strings with fuses, busbars, SPDs and a DC isolator. Check string fuse ratings against the module series fuse rating.
Earthing and surge protection
Bond module frames and mounting rails to the earthing system; use listed bonding hardware or dedicated earthing conductors. Earth the inverter and AC distribution as required. Install DC and AC surge protective devices, commonly Type 2, near the equipment, with short, straight leads. A lightning protection system, where required, uses air terminations and down conductors; PV equipotential bonding must follow the design.
Routing and dressing
Route cables in trays or conduits, avoid sharp edges, maintain bend radius, support at intervals, and create a drip loop before entry. Separate DC and AC where practical, protect against rodents, and do not leave connectors lying in water.
Worked example
A 30 m DC run carries 10 A at 600 V. With 6 mm² copper and resistivity 0.0175 Ω·mm²/m, voltage drop = 2 × 30 × 10 × 0.0175 ÷ 6 = 1.75 V, or 0.29% of 600 V, well within 3%. With 2.5 mm² it would be 4.2 V, or 0.7%, still acceptable here, but current rating and mechanical robustness also matter.
Traps
Using AC cable outdoors on DC; unmating MC4 under load; earthing only the inverter and not frames; omitting DC SPD; leaving water traps; mixing connector brands that do not interlock.