Wiring, Cabling, Connectors, Earthing and Protection
Cable sizing
Wiring, Cabling, Connectors, Earthing and Protection covers safe current paths and fault protection. Select cable for current-carrying capacity, voltage drop and mechanical protection. Voltage drop should generally be kept below about 3 % on DC circuits; long DC runs need larger copper. Use UV-resistant, double-insulated DC cable outdoors, correct polarity and matched connectors. AC and DC circuits should be separated and clearly labelled.
Connectors, earthing and protection
MC4-type connectors must be the same brand and type when mated, crimped with the correct tool and checked for tightness. Earthing bonds module frames, mounting rails and equipment to earth. Protective devices include DC fuses or breakers, AC breakers, surge protective devices (SPDs) and RCDs where required. Battery circuits need a fuse close to the battery positive terminal.
Worked example
A 24 V DC load draws 10 A through a 20 m one-way cable run. Using 4 mm² copper, resistivity 0.0175 Ω·mm²/m: loop resistance = 0.0175 × 40 / 4 = 0.175 Ω. Drop = 10 × 0.175 = 1.75 V, which is 7.3 % of 24 V, too high. With 10 mm², resistance = 0.070 Ω, drop = 0.70 V (2.9 %), which is acceptable.
Traps
Do not use ordinary AC flexible cable as a substitute for UV-rated DC cable. Do not earth the positive and negative of a battery bank together. Do not rely on connector contact alone for earthing; use a proper bonding conductor.