Fault-finding is a daily core competence and a separate assessment criterion. Here is the method: symptom analysis, the halving method, systematic narrowing along the signal path, the four classic fault types and how to locate breaks, short circuits, earth faults and poor connections with a multimeter and megger — safely, per DS/EN 50110-1.
Introduction
Much of an electrician's day is troubleshooting: something is not working and you must find out why — quickly safely and without swapping expensive parts randomly. Troubleshooting is therefore an independent assessment criterion on the journeyman's exam. Unlike the planned verification on commissioning (see the verification entry) you work here on a system already in operation and faulty — and so both a systematic method and heightened safety apply according to DS/EN 50110-1.
Start with symptom analysis
The best troubleshooting begins with understanding the fault, not by grabbing a meter. Ask systematically:
- 01What works and what does NOT work? The boundary between functioning and defective immediately narrows down the error.
- 02Did it arise suddenly or gradually? After a change, a weather shift, a specific load?
- 03Is it constant or intermittent? Intermittent faults often point to loose connections, temperature or vibration.
- 04What has changed since it last worked? New load, repair, moisture, rodents?
Bisection method
The bisection method is the most important tool for fault-finding. Instead of measuring from one end to the other, you measure IN THE MIDDLE of the suspected section: if the signal is good here, the fault is in the other half — if it's gone, the fault is in the first. Then you halve again. A long chain is narrowed down in a few measurements instead of many, because each step halves what's left to search in.
Follow the signal path systematically
All fault-finding follows a chain from source to load: supply → protection (fuse/RCD) → switch/control → conductor → load, with PE and neutral as return path. Go through the chain one link at a time and confirm by measurement how far 'the good signal' reaches. The place where the voltage disappears (or the circuit breaks) is the fault location or just before it.
The four classical error types
| Error type | What's happening | Typical measurement |
|---|---|---|
| Interruption (open) | The conductor is broken — no current | No continuity; voltage disappears at the break |
| Short circuit (short) | Two conductors touch — protection trips | Very low resistance between two conductors |
| Earth fault (earth fault) | Active conductor to earth/PE — HPFI couples | Low insulation resistance to PE (megger) |
| Contact resistance | Poor joint — heat, voltage drop | Voltage drop across the joint under load; thermography |
Contact resistance (the poor, hot joint) is the insidious one: the circuit 'works' almost, but loses voltage and develops heat at the joint. It is found by measuring the voltage drop across the joint while under load — or with a thermal camera, where it lights up.
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