MCB - Miniature Circuit Breaker
An MCB protects against overcurrent (overload and short circuit) in the street light feeder cable. It trips when current exceeds its rated value for long enough to indicate a fault. Rating selection: MCB current rating = total load current ÷ power factor, with 25% headroom. For 10 × 40W LED lights (PF 0.95): total current = (10 × 40W) ÷ (230V × 0.95) = 1.83A. Use 4A MCB (next standard size above 1.83A × 1.25 = 2.3A). MCB type: use Type B for LED street lights (trips at 3–5× rated current for short circuits). Type C (trips at 5–10×) is used when high inrush current loads are present - LED drivers have low inrush, so Type B is appropriate.
ELCB/RCCB - Earth Leakage Protection
ELCB (Earth Leakage Circuit Breaker) or RCCB (Residual Current Circuit Breaker) detects leakage current to earth - the critical safety device for outdoor street light circuits. It trips when it senses even a small current flowing to earth (typically 30mA threshold), indicating insulation failure or a live pole. 30mA RCCB: the standard for outdoor circuits - this level is below the threshold that causes cardiac fibrillation (the most dangerous effect of electric shock). 100mA RCCB: for feeder circuit protection against fire (leakage current that could heat a cable). Installation: every street light feeder circuit must have both an MCB (overcurrent) and a 30mA RCCB (earth leakage). Use a combined RCBO (RCCB + MCB in one unit) for compact panels.
Common Mistakes in Street Light Panel Design
Using only MCB without RCCB: the most dangerous omission - the MCB will not trip from an earth fault unless the fault current exceeds its overcurrent threshold (which requires a dead short). A high-resistance insulation fault leaking 50mA to a pole will not trip the MCB but will kill a person who touches it. Over-rating the MCB: using a 16A MCB on a 2A load means the MCB never trips even during serious overloads that heat cables and cause fires. Sharing RCCB across multiple circuits with different earth paths: nuisance tripping from normal leakage currents. Each street light feeder circuit should have its own 30mA RCCB. Not using time-delay RCCB on long cable runs: long cables have natural capacitive earth leakage - time-delay (S-type) RCCB at 100mA on the main incomer, with 30mA instant-trip on individual feeders.
