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C3 and FI: improvement recommended, and further investigationWhen should you use FI?

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The question at the end: Borderline between C3 and FI. Which? The answer is in the notes below.

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The current wording for FI is “Further investigation is advised” (Guidance Note 3 · Table 3.5 · p.132), and Guidance Note 3 says FI should only be used in exceptional circumstances. Best Practice Guide 4 pushes the same way: give a real code wherever you can.

Give it a code between C1 and C3 if you possibly can. Use FI sparingly

The clearest example is insulation resistance:

FindingNotBut
Insulation resistance below the minimum — say 0.8 MΩ line-and-neutral to earthFIC2

The logic: a failed insulation resistance test needs investigating and dealing with straight away. C1 and C2 both carry that urgency. C3 does not. So it belongs at C2.

A reminder on expected values. As low as 1 MΩ would conform. For comparison, Guidance Note 3 · p.70 says that in new installations a value below 20 MΩ should be investigated.
✋NC is not an outcome on the EICR. Best Practice Guide 4 uses NC for non-compliant in its own tables, but there is no NC box on the report. On the paperwork it has to become a C3, an FI, or N/V.

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