Power Trip in Singapore: Diagnosis Before Rewiring

When the lights go out in an HDB or condo unit and the MCB has tripped, three questions decide everything that happens next: which device tripped, on which circuit, and under what load. Skip those questions and you end up replacing parts that were not the problem.

Three faults that look the same from outside the DB

• Short circuit — a near-zero-ohm path between live and neutral (or live and earth). MCB trips fast.
• Overload — load above the rated current of the protective device. MCB trips after seconds to minutes of sustained load.
• Earth leakage — current returning via the protective earth instead of neutral. RCD / RCBO trips at 30 mA.

The 15-minute on-site diagnosis sequence

• Open the DB door and read which device tripped (MCB only, RCBO only, or main RCCB)
• Isolate the affected circuit, restore the rest of the DB
• Disconnect appliances on that circuit and re-energise — if it holds, the fault is downstream of the DB
• Re-introduce appliances one by one — the fault often surfaces on a specific appliance, not the wiring
• If the circuit will not hold even with no appliances plugged in, the fault is in the wiring itself

Instruments that confirm the diagnosis

An insulation resistance tester (megger) at 500 V DC tells us whether the conductor insulation is intact. A loop impedance tester confirms the fault path back to the source. A clamp ammeter tells us the actual load on the circuit. Without these readings, "must be the wiring" is a guess.

What "rewire" actually means

A rewire replaces the cable and the protective device on a circuit. It is the right scope where the megger says the insulation is failing or the cable is undersized for the load. It is the wrong scope where a single appliance is the actual culprit. Rewiring is licensed work — carried out by an LEW on the EMA ELISE Licensed Electrical Worker directory.