Every defect you find during a periodic inspection has to go somewhere on the Schedule of Items Requiring Attention. The code you put next to it — C1, C2, C3, or FI — determines whether your client needs a remedial contractor on site this afternoon or whether the report can go out as Satisfactory. Get the code wrong and you are either overstating the risk (which costs your client money and damages your credibility) or understating it (which is a serious safety and liability issue).
This guide works through each code in detail: what it actually means under BS 7671, when to use it, where electricians routinely get it wrong, and how the codes feed into the overall outcome of the report. It assumes you are a qualified electrician who knows the regs — this is not a beginner’s overview, it is a practical working reference.
The Four Classification Codes: What They Actually Mean
The codes come from BS 7671:2018 (as amended) and the associated Guidance Note 3 published by the IET. Each one has a specific meaning. They are not a sliding scale of “how bad is it” — they are distinct categories with different implications for the overall report outcome and for what action is required.
The classification codes are about risk to persons and property, not about your personal opinion of the installation quality. An observation you personally think is poor practice may not meet the threshold for any code if it does not present a genuine risk or compliance breach.
| Code | Full meaning | Report outcome | Action required |
|---|---|---|---|
| C1 | Danger present — risk of injury | Unsatisfactory | Immediate remedial action required. Isolation may be necessary. |
| C2 | Potentially dangerous | Unsatisfactory | Urgent remedial action required. |
| C3 | Improvement recommended | Satisfactory (if no C1/C2) | Improvement recommended but not obligatory. |
| FI | Further investigation required without delay | Unsatisfactory | Condition cannot be assessed without further investigation. |
C1 — Danger Present
C1 means there is an immediate risk of electric shock or fire. Not a theoretical risk — a real, present one. Think exposed live conductors, missing protective conductors, a consumer unit with its blanking plates missing and live busbars accessible, or a socket outlet where the earth terminal is disconnected and the socket is in regular use. The key test is: could a person be injured right now without doing anything unusual?
When you find a C1, you have a duty to inform the client immediately. In most cases you should isolate the affected circuit or equipment before you leave. If you cannot isolate it, you need to clearly document this and advise the client not to use that circuit until it is repaired. C1 items cannot be left for the remedial contractor to find in two weeks.
The EICR must record the C1 defect and note what immediate action was taken, including whether isolation was carried out.
C2 — Potentially Dangerous
C2 is the code that causes the most confusion. “Potentially dangerous” means that the defect does not present an immediate danger in normal use, but could become dangerous under foreseeable fault conditions or changed circumstances. An overloaded circuit that has not yet caused a fire. A missing RCD on a bathroom circuit — no immediate danger, but if a fault occurs the protection is not there. Inadequate earthing that would fail to operate the protective device in the event of a fault.
The distinction from C1 is that someone would need to do something, or something else would need to go wrong, before injury occurs. The risk is real and urgent, but it is not happening right now.
C2 makes the report Unsatisfactory. The client needs to arrange remedial work, and you should advise them on the urgency. “Urgent” in this context generally means weeks, not months, but it does not require isolation on the day (unless you judge that isolation is necessary for safety).
C3 — Improvement Recommended
C3 is the only code that allows a Satisfactory overall outcome. It is used where an observation does not meet current standards but does not present a safety risk in its current state. The textbook example is single-pole lighting switches on circuits that were installed before the current regulations required double-pole isolation. Technically non-compliant with current regs, but not dangerous.
C3 should be used when you are recommending an upgrade to current standards rather than identifying a genuine safety concern. It is also appropriate for recommendations where the standard has changed since the installation was made and the existing installation was compliant at the time.
A report with only C3 codes is still Satisfactory. The client is not obliged to carry out the improvements, though they should be given a clear explanation of what is recommended and why.
FI — Further Investigation Required Without Delay
FI is the most misunderstood code in practice. It does not mean “I could not be bothered to look” or “I am not sure what is going on here.” It means that a specific condition was found that requires further investigation before it can be classified, and this investigation must happen without delay.
The operative phrase is “without delay.” FI is not a way to park a problem. It is used when you genuinely cannot determine the safety status of an observation without further work — for example, you find signs of heat damage to cables concealed in a wall and cannot assess the extent of the damage without opening up the wall, or you find an RCD that is intermittently failing to operate but you cannot determine the cause during the inspection period.
FI makes the report Unsatisfactory. The client needs to arrange for the further investigation to be carried out, after which the affected items should be re-classified as C1, C2, or C3 as appropriate.
How Classification Affects the Overall Report Outcome
The overall outcome of an EICR is either Satisfactory or Unsatisfactory. The rules are straightforward but worth spelling out explicitly because this is where reports go wrong.
A single C1 code makes the report Unsatisfactory regardless of anything else on the report. No exceptions.
A single C2 code makes the report Unsatisfactory. Even one C2 alongside dozens of C3 codes gives an Unsatisfactory outcome.
FI also results in an Unsatisfactory outcome because the safety status cannot be confirmed until further investigation is completed.
C3 codes alone do not prevent a Satisfactory outcome. The installation has issues that would benefit from improvement but does not have a safety problem.
This matters enormously in practice. Landlords in England and Wales are legally required to hold a valid EICR under the Electrical Safety Standards in the Private Rented Sector Regulations 2020. An Unsatisfactory report requires remedial work within 28 days (or sooner if the report specifies). A Satisfactory report allows the landlord to continue operating. Getting this wrong has direct legal consequences for your client.
The “No Code” Observation
Not everything you note on an EICR has to carry one of the four codes. Observations that are purely for information — confirming the type of wiring system, noting the estimated age of the installation, recording limitations of the inspection — do not need a classification code. Only observations that identify a defect, departure from current standards, or condition requiring further investigation need a code. Over-coding your report with C3s on everything you happen to notice clutters the Schedule and makes it harder for the client and the remedial contractor to understand what actually needs doing.
Common Classification Mistakes in Practice
These are the errors that come up again and again when EICRs are reviewed, disputed, or audited. Most come down to not applying the correct test for each code.
Using C2 When C1 Is Correct
The most common serious error. An exposed live conductor is a C1. A consumer unit with live parts accessible to touch is a C1. Some electricians downgrade these to C2 because they feel C1 is “too serious” or because they do not want to have to isolate the circuit. This is wrong, and it exposes you to significant liability if an injury occurs after you have issued the report.
Apply the test: can a person be injured right now in normal use without anything else going wrong? If yes, that is C1. The fact that nobody has been injured yet does not make it C2.
Using C3 When C2 Is Correct
Equally common but in the opposite direction. An RCD not operating within the required time is not a C3 — it is C2 because the protective device may fail to operate in the event of a fault. A circuit with Zs values exceeding the maximum permitted for the protective device is not a C3 — it may not disconnect in time under fault conditions.
C3 is for observations where the installation differs from current standards but is not unsafe. If the departure from standards creates a genuine fault protection risk, that is C2 territory.
This is the most serious error on an EICR. If you have a C2 or above — an RCD not operating correctly, inadequate earth fault loop impedance, missing supplementary bonding in a bathroom — and you classify it as C3 to give the client a Satisfactory outcome, you are understating the risk and issuing a misleading document. This is a professional conduct issue and a potential liability issue. The correct answer to a client who wants a Satisfactory outcome but has a C2 problem is: fix the C2 first, then the report can be Satisfactory.
Over-Using FI to Avoid Making Decisions
FI has a specific purpose: conditions that genuinely cannot be assessed without further investigation. It is not a catch-all for “I am not sure about this” or “I did not have time to investigate properly.” If you can assess the safety of something with the information available, you should classify it. If you cannot access an area or complete a test, that should be recorded as a limitation of the inspection, not necessarily as an FI.
Ask yourself: is there a specific condition here that I have identified which requires further investigation before I can classify it? If so, FI is appropriate. If you simply could not access an area, record the limitation instead.
Not Giving a Clear Location for Each Observation
This is not a classification error, but it renders the classification useless. Every item on the Schedule of Items Requiring Attention must have a location specific enough that someone else can find it. “Consumer unit — circuit 6” is not enough. “Consumer unit in understairs cupboard, circuit 6 (ring final circuit serving kitchen sockets), neutral conductor loose on neutral bar” is what a good observation looks like. The classification code only does its job if the remedial contractor can find what needs fixing.
Conflating “Not to Current Standards” with “Dangerous”
An installation that was installed correctly to the standards in force at the time is not automatically defective just because the standards have been updated. Single-pole lighting switches on older installations, aluminium wiring in properties from the 1960s and 1970s, and older consumer units without arc-fault detection are not automatically C2 items. They may be C3 recommendations, or they may simply be observations with no code if the overall condition is acceptable. The test is always whether there is a present safety concern, not whether the installation matches the current 18th Edition exactly.
Putting It Together: Writing Observations That Stand Up
A classification code is only as good as the observation it is attached to. When you write up your Schedule of Items Requiring Attention, each entry should contain four things: what the defect is, where it is, why it has been given that classification code, and what action is required.
For a C1, add what immediate action was taken — whether the circuit was isolated, whether the client was verbally notified, whether written notice was given. For an FI, state specifically what further investigation is needed and why the condition cannot be assessed without it.
If you are producing the EICR digitally using a structured tool, these prompts should be built into the workflow. The EICR form in CertBox structures the Schedule this way, reducing the chance of a code without a clear justification or a defect without an adequate description.
The overall standard to hold yourself to: if your report were reviewed by a technical assessor, or if a client disputed an Unsatisfactory outcome, could you justify every code on the Schedule with clear evidence and reasoning? If you can, the report is solid. If you cannot, revisit the classification before you issue it.
For new installation work, the companion document to the EICR is the Electrical Installation Certificate, which records that new work meets BS 7671 at the point of installation. Both documents feed into the long-term compliance record for any electrical installation.
EICR Classification Built Into the Workflow
CertBox structures the Schedule of Items Requiring Attention so every observation needs a code, a location, and a description before you can complete the report. Fewer missed items, better-documented decisions.
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Published February 2026. This article is for general guidance only and does not constitute legal or professional advice. Always refer to BS 7671:2018 (as amended), IET Guidance Note 3, and your competent person scheme guidance for definitive requirements.
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Published February 2026. This article is for general guidance only and does not constitute legal or professional advice. Always refer to the relevant standards and consult qualified professionals for definitive requirements.