Knowledge article
EICR Sampling Explained
EICR sampling is testing a representative proportion of circuits on large installations — the sampling basis must be recorded so the result stays valid.
Sampling means testing a representative proportion of an installation's circuits rather than every single one. It is a recognised approach for periodic inspection of large installations, where testing 100% of circuits would be impractical or disproportionately disruptive.
When sampling is appropriate
Sampling is used on installations with many circuits and distribution boards — large commercial, industrial or institutional sites. It is not normally needed for a small domestic installation, where full testing is straightforward.
How responsible sampling works
- A defensible proportion of circuits is selected, spread across boards and circuit types.
- The sampling basis (what percentage, chosen how) is recorded on the report.
- If defects are found in the sample, the inspector increases the sample size to establish whether the problem is widespread.
Why the sampling basis matters
A "Satisfactory" result based on undisclosed, minimal sampling is misleading. Recording the sampling basis keeps the report honest and lets the duty holder judge how much assurance it provides — and plan future inspections to cover circuits not sampled this time.
Sampling is closely related to EICR limitations: both are about being transparent regarding the extent of the inspection.
Frequently asked questions
Is sampling allowed under BS 7671?
Yes. For periodic inspection of larger installations, testing a representative sample is recognised practice, provided the sampling basis is recorded and any items found are investigated. If defects are found in the sample, the sample size is normally increased.
More in this topic
Code explanation
EICR C1 Code: Danger Present
A C1 on an EICR means danger is present and a risk of injury exists. It requires immediate action and always makes a report Unsatisfactory.
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Difference Between C1 and C2 on an EICR
C1 means danger is present now and requires immediate action; C2 means potentially dangerous — safe now but a fault could make it dangerous. Both fail an EICR.
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EICR C2 Code: Potentially Dangerous
A C2 on an EICR means potentially dangerous — no immediate danger, but a fault could make it dangerous. It requires urgent remedial action and fails the report.
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Difference Between C2 and C3 on an EICR
C2 is potentially dangerous and fails an EICR, requiring urgent remedial work; C3 is a non-urgent improvement recommendation that keeps the report Satisfactory.
Learn moreThis article provides general guidance and distinguishes legislation, British Standards and good practice. It is not legal advice. Always confirm the specific duties applying to your property and tenure.