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.
Apprentice mode
Full walk-through — the why, what readings mean, mistakes & safety.
Likely causes
Ranked from most to least likely.
- 1
Poor earth/CPC connection on the circuit
Most likelyA loose, undersized, or broken protective-earth connection raises the loop impedance.
- 2
Long run / undersized conductors
#2A long circuit or undersized conductors increase impedance.
- 3
Main earthing / bonding issue
#3A problem at the main earth or bonding affects the loop.
- 4
Loose connection adding resistance
Least likelyA high-resistance joint anywhere in the loop raises the reading.
Reports are saved on this device to reflect what you actually find.
Testing sequence
Work through one test at a time. Expected reading and what each result means.
On the tools? Job Mode shows one test at a time with thumb-sized buttons — your place and readings carry straight over.
Enter Job ModeRe-test the loop impedance and check the protective-earth (CPC) continuity on the circuit per procedure.
Loop impedance and earth continuity within the values your procedure allows.
If within limits, re-confirm the original reading/test method.
Out of limits — trace the earth path and connections for the cause.
View all expected readings at once
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.
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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.
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Learn the theory
How the gear and circuits behind this fault actually work.