High earth-fault loop impedance / earthing concern
Testing shows a high earth-fault loop impedance (or an earthing concern) on a circuit — meaning protection might not operate fast enough on a fault, which is a safety issue to resolve.
Safety first
A high loop impedance/poor earth can mean protection won't clear a fault quickly — a real shock/safety risk. This is licensed testing and rectification; follow your test procedures.
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.
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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
High loop impedance
→ step 2 - 2decision
On re-test, is the loop/earth within allowed values?
Yes→ step 3No→ step 4 - 3result
Within limits — re-confirm the original reading/method.
- 4decision
Are the earth connections/bonding sound and correctly sized?
Yes→ step 5No→ step 6 - 5result
Consider conductor sizing / run length.
- 6result
Poor earth/bonding — rectify and re-test.
Common mistakes apprentices make
- Treating a high loop reading as 'close enough'.
- Not checking the main earthing/bonding.
- Overlooking a loose earth connection.
- Ignoring conductor sizing/run length.
When to stop & escalate
Earthing/loop-impedance issues are a safety matter and licensed work — rectify and re-test to confirm protection will operate correctly. Don't leave a circuit in service with a known earthing concern.
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
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.
No supply at a socket-outlet or point
A socket-outlet or point is dead — nothing plugged in works — while other points may be fine. A bread-and-butter 'trace it back' fault.
MCB (circuit breaker) keeps tripping
A circuit breaker trips repeatedly — instantly on reset, or after a load runs for a while — and you need to tell a short from an overload from a faulty breaker.
Learn the theory
How the gear and circuits behind this fault actually work.