Lost or high-resistance neutral
Strange symptoms across a circuit or installation — voltages going high and low on different loads, flickering, equipment damage — pointing to a lost or high-resistance neutral.
Safety first
A lost neutral can put dangerous voltages on equipment and exposed parts. Treat the whole affected area as hazardous, isolate, and prove dead. This can damage many devices at once.
Isolate, lock out / tag out, and prove dead before working unless a live test is specifically required, authorised, and carried out under proper supervision. Always follow local regulations, your site procedures, and the equipment manufacturer's documentation.
Full detail — causes, the why, and common mistakes.
Likely causes
Ranked from most to least likely.
Premium fault tree
The full ranked causes, test sequence and flowchart for this fault are part of Sparkie Sidekick Pro.
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Testing sequence
Work through one test at a time. Expected reading and what each result means.
Full test sequence
The step-by-step test flow with expected readings for this fault is part of Sparkie Sidekick Pro.
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Fault-finding flowchart
The same logic as a decision tree.
- 1start
Suspected lost neutral
→ step 2 - 2decision
Do some loads over-volt and others under-volt, varying with load?
Yes→ step 3No→ step 4 - 3decision
Is the local neutral continuous and tight (incl. the board)?
Yes→ step 5No→ step 6 - 4result
Stable voltages — likely not a lost neutral; look elsewhere.
- 5result
Investigate shared neutrals and the supply-side neutral (escalate if supply).
- 6result
Broken/loose neutral — repair it.
Common mistakes apprentices make
- Chasing individual loads instead of recognising the high/low pattern.
- Energising equipment before fixing the neutral (risking damage).
- Overlooking a loose neutral bar at the board.
- Not considering a supply-side neutral fault.
When to stop & escalate
A supply-side (utility/distribution) neutral fault is upstream — raise it urgently as it can be dangerous and affect the whole installation. Repairs to the installation neutral must be by a qualified person, with everything proven dead first.
If you're past your competence, authorisation, or the safe limits of the job — stop and hand it on. There's no fault worth getting hurt over.
Related faults
Three-phase equipment single-phasing (lost a phase)
Three-phase equipment is misbehaving — motors humming, struggling, overheating, or tripping — because one phase has been lost somewhere between the supply and the load.
Loose connection overheating (discolouration / smell)
A terminal or connection is overheating — discoloured insulation, a burning smell, or heat you can feel — a common cause of nuisance faults and a real fire risk.
Voltage drop on a long cable run
Equipment at the end of a long run misbehaves — dim lights, a contactor that won't hold, a motor struggling — because volt-drop along the cable leaves too little voltage at the load.
Learn the theory
How the gear and circuits behind this fault actually work.