A consumer unit replacement always needs an Electrical Installation Certificate (EIC), never a Minor Works certificate, and in a dwelling in England or Wales it is notifiable under Part P, with the compliance certificate due within 30 days of completion. Before the old board comes off, survey what you are inheriting: earthing, bonding, Ze, cpc continuity and an insulation resistance reading of at least 1 MΩ, the figure both BS 7671 and Electrical Safety First's Best Practice Guide 1 (Issue 5.1, October 2025) work to. Circuits with immediate or potential danger are repaired or left disconnected. Everything you reconnect is tested and recorded on the schedule of test results.
- Certificate: an EIC with schedules of inspection and test results (Regulations 644.1 and 644.3), plus Part P notification in England and Wales.
- Recommend an EICR first. If the client declines, Best Practice Guide 1 sets a minimum pre-work survey: Ze, cpc continuity on every final circuit, loop impedance at accessible sockets and whole-installation insulation resistance.
- Regulation 132.16: earthing, bonding, tails and the distributor's equipment must be adequate before you alter anything.
- A circuit with a C1 or C2 level defect is fixed or left disconnected and labelled. An RCD is not a repair.
- The new board: non-combustible enclosure (421.1.201), Type A RCBOs or RCDs, an SPD unless the owner declines (443.4.1), the manufacturer's own devices (536.4.203) and correct labelling (Section 514).
- There is no legal duty to bring the whole installation up to the current edition, but the work must leave it no worse than you found it.
Which certificate does a consumer unit change need?
An EIC is the BS 7671 document for a new installation, a new circuit, or an alteration that affects more than one circuit or the origin. A Minor Electrical Installation Works Certificate covers an addition or alteration to one existing circuit, which a board change is not. See EICR vs EIC: What's the Difference? (and Minor Works) and Minor Works Certificate: When to Use It (and When Not To) for where the line sits.
The EIC certifies your work: the new assembly, its devices and the reconnection. It does not certify the existing wiring, which is why the "comments on existing installation" box matters so much on this job.
| Part of the EIC | What to record for a consumer unit change |
|---|---|
| Description and extent | "Replacement of consumer unit and reconnection of existing final circuits. Existing wiring not renewed." Tick alteration, not new installation (some scheme forms have a consumer unit replacement box) |
| Supply characteristics | Earthing arrangement, nominal voltage, measured Ze and prospective fault current, cut-out fuse type and rating |
| Earthing and bonding | Earthing conductor and main bonding conductor sizes, what each is bonded to, continuity confirmed |
| Comments on existing installation | Every defect found that you were not engaged to fix, plus any circuit left disconnected and why |
| Schedule of inspections | Items relevant to the new board and the reconnected circuits |
| Schedule of test results | One row per circuit: device type and rating, conductor sizes, R1+R2 or R2, ring r1/rn/r2, insulation resistance, polarity, Zs, RCD time |
For the form itself, see Electrical Installation Certificate (EIC) Explained.
Is a consumer unit replacement notifiable under Part P?
Yes. In England, replacing a consumer unit in a dwelling is one of the three notifiable categories in Approved Document P, alongside new circuits and work in special locations. Wales keeps a longer notifiable list and a board change is on that too. A registered competent person notifies through their scheme within 30 days of completion, and the client receives a Building Regulations compliance certificate as well as your EIC. An electrician who is not registered has to notify building control before starting, or use a registered third-party certifier. The detail is in Part P notification: what to notify, how, and by when.
Scotland works under the Building (Scotland) Regulations, where a like-for-like board change does not normally need a warrant. It still needs an EIC to BS 7671.
What survey do I need before a planned or a distress change?
Best Practice Guide 1, published by Electrical Safety First with NICEIC, NAPIT, the ECA, SELECT, the IET and BEAMA among the contributors, draws a clear line between the two.
For a planned change, strongly recommend a full EICR first. If the client will not pay for one, a pre-work survey must be done before any work starts. The guide's minimum is below.
| Pre-work check | What it tells you |
|---|---|
| Ask the client about known defects, tripping and past alterations | Where to look first |
| Internal visual inspection of the existing board | Overheating, doubled-up conductors, shared neutrals, missing cpcs |
| External inspection and measurement of Ze | Whether the means of earthing is there and sound |
| cpc continuity at the end of each final circuit | Circuits with no earth, before you fit a metal enclosure next to them |
| Loop impedance at readily accessible socket-outlets | High readings, broken rings, polarity clues |
| Insulation resistance of the whole installation at the board | Whether new RCDs will hold |
For a distress change, such as a burnt-out main switch, there is no time for an EICR. The guide still expects a survey for immediate dangers and for anything that would trip an RCD, and confirmation that the earthing, main bonding, fault protection, meter tails and supply polarity are right.
Record the survey figures. They are your evidence of what you inherited, and they let you price the extra work before the client has a house with no power.
What has to be adequate before the old board comes off?
Regulation 132.16 says no addition or alteration shall be made to an existing installation unless the rating and condition of existing equipment, including the distributor's, is adequate for the altered circumstances and the earthing and bonding are adequate. For a board change that means four things.
Means of earthing. Identify the arrangement (/guides/earthing-arrangements-tn-s-tn-c-s-tt-explained) and measure Ze with the earthing conductor disconnected and the installation isolated, then reconnect before anything is energised. See What is Ze? External earth fault loop impedance. A TT installation needs the electrode tested too: Earth Electrode Testing for TT Systems: Methods and Limits.
Main protective bonding. Water, gas, oil and structural steel where they are extraneous-conductive-parts, with continuity measured back to the main earthing terminal. On PME the usual minimum is 10 mm². Best Practice Guide 1 accepts that an existing 6 mm² bonding conductor could be deemed adequate where it has been in place a long time and shows no sign of thermal damage, and that a 6 mm² or 10 mm² earthing conductor with 25 mm² tails can be adequate if Regulation 543.1.3 is met. Some distributors set their own larger minimums, so check. Background in What is main protective bonding? Explained.
Tails and cut-out. The guide allows that 16 mm² tails on a 100 A cut-out could be adequate where maximum demand, after diversity, stays within the tails' capacity. Damaged tails, a cracked cut-out or signs of overheating go to the distributor or supplier before you start.
Isolation. You are not entitled to pull the cut-out fuse unless authorised. If there is no isolator, arrange one through the supplier: Smart Meters and Isolators on EICRs: What to Record.
Measure prospective fault current at the origin as well. A domestic board built to BS EN 61439-3 carries a 16 kA conditional rating when fed through a cut-out fuse of 100 A or less, which is why 6 kA devices are accepted in it. See What is prospective fault current (PFC)? Explained.
Which existing circuits can I reconnect, and which stay off?
Best Practice Guide 1 uses the EICR scale. Immediate danger is a C1, potential danger a C2. A circuit with either is corrected or left disconnected from the new board. Lesser defects should ideally be put right, and if the client will not pay they go in the comments on the existing installation.
| Finding on the existing circuit | Level | What to do |
|---|---|---|
| Insulation resistance below 1 MΩ | C2 | Fault-find. If not cleared, do not reconnect |
| Lighting circuit with no cpc feeding metal fittings or switches | C2 | Rewire, add a cpc, or go all-insulated and Class II |
| No cpc continuity at a socket-outlet | C2 | Repair before reconnection |
| Broken ring final on a 32 A device | C2 | Repair, or reconnect as two radials on suitably rated devices |
| Reversed polarity | C2 | Correct it |
| Shared neutral between two circuits | Usually C2 | Separate, or put both circuits on one device as a single circuit |
| Zs above the device maximum | C2 unless the RCD gives fault protection | Find the high resistance first; do not lean on the RCD blindly |
| Cable undersized for the existing fuse | C2 | Fit a device rated to the cable |
| No RCD on a buried cable at less than 50 mm | C3 on an EICR | Solved by the new board |
Low insulation resistance
Separate line to earth from neutral to earth, then disconnect loads. Immersion heaters, cooker elements, outside lights and old fluorescent fittings are the regulars, and a reading that recovers with the load out is an appliance fault, not a cable fault. Split the circuit at a mid-point to halve the search. The full method is in Low Insulation Resistance: Finding the Fault on Site. Remember Regulation 531.3.2: leakage downstream of an RCD should not exceed 30% of its rating, so 9 mA on a 30 mA device. A circuit that scrapes past 1 MΩ can still be a nuisance tripper.
Lighting circuits with no cpc
Common in 1960s houses. The guide's order of preference is: rewire; or install a cpc with a connection at every accessible point; or, where the client refuses both, replace every metal and Class I fitting and accessory with all-insulated or Class II. Only as an absolute last resort does Annex B's risk assessment apply: continuity from the earthing terminal to each Class I fitting of 1 Ω or less, and insulation resistance of at least 1 MΩ, including to any unearthed metalwork. Fail that and the circuit stays off. Where you do reconnect, fix the black-on-yellow warning notice at the board stating which circuits have no provision for earthing metal equipment.
Shared and borrowed neutrals
Two-way landing lights are the usual culprit. An RCBO sees the imbalance and trips the moment both circuits are loaded. Find them with the method in Borrowed Neutrals: How to Find, Test and Code Them before you commit to an all-RCBO board.
What does the new consumer unit need to comply with?
| Requirement | Regulation | In practice |
|---|---|---|
| Non-combustible enclosure, assembly to BS EN 61439-3 | 421.1.201 | Steel board; close unused knockouts |
| All conductors of a circuit through one entry in a steel enclosure | 521.5.1 | Line, neutral and cpc together; no separate holes for tails |
| Enclosure integrity | 416.2 | IP2X generally, IP4X on the top surface; grommet strip on cut edges |
| Additional protection by 30 mA RCD | 411.3.3, 411.3.4, 522.6.202 | Sockets to 32 A, domestic lighting, concealed cables: in effect every final circuit |
| RCD type to suit the load | 531.3.3 | Type A minimum; Type AC only where no DC component is possible |
| Division of circuits | 314.1 | One fault should not take out the house; favours RCBOs |
| Surge protection | 443.4.1 | Type 2 SPD unless the owner declines |
| Arc fault detection | 421.1.7 | Required on sockets to 32 A in specified premises, recommended elsewhere |
| Direction of power flow | 530.3.201 | Bidirectional devices where PV or battery can back-feed |
| Rated current and overload of switches and RCCBs | 536.4.202 | Do not rely on diversity alone; coordinate with the cut-out fuse |
| Devices declared suitable by the assembly maker | 536.4.203 | No mixing brands in one board |
| Connections | 526.1, 134.1.1 | Torque every terminal to the maker's figure |
RCBOs or split load? BS 7671 does not mandate RCBOs, but Regulation 314.1 and Best Practice Guide 1 both point that way, the guide recommending Type A RCBOs on all circuits or sufficient Type A RCDs. The trade-offs are in RCBO vs RCD Split-Load Boards: Which to Fit and Why.
Surge protection. Under 443.4.1 an SPD is required where the consequence of an overvoltage could be serious injury or loss of life, failure of a safety service, or significant financial or data loss. In all other cases it is still required unless the owner declares it is not and accepts the risk. Fit a Type 2 device with short, straight leads as standard. More in Surge Protection (SPD) Requirements: Section 443 Explained.
AFDDs. Regulation 421.1.7 requires them on single-phase socket-outlet circuits up to 32 A in high rise residential buildings, HMOs, purpose-built student accommodation and care homes, and recommends them elsewhere. For an ordinary house, discuss it and note the decision. See AFDD Requirements: Regulation 421.1.7 Explained (A4:2026).
Back-feed. Regulation 530.3.201, added by Amendment 3 in July 2024, makes you consider whether each device is unidirectional or bidirectional. An RCBO marked with line and load terminals on a PV or battery circuit is the classic mistake: Solar PV Installation Certificate: Section 712 and the EIC.
Labels. Section 514 wants a durable circuit chart, the six-monthly RCD test notice, the periodic inspection notice, and warnings for any disconnected circuit. Leave spare ways. The guide suggests allowing for EV charging, PV and battery storage, and recommends Grade D mains smoke alarms where there are none.
What is the test sequence after the change?
Dead tests first, then live, in the BS 7671 Chapter 64 order. Best Practice Guide 1 lists the minimum for existing circuits.
| Step | Test | Note for a board change |
|---|---|---|
| 1 | Continuity of each cpc (R1+R2 or R2) | Continuity Testing: R1+R2 Method, Wander Lead and Values |
| 2 | Ring final continuity, every ring | Ring Final Circuit Testing: r1, rn, r2 and R1+R2 Explained |
| 3 | Insulation resistance, 500 V DC, 1 MΩ minimum | Disconnect the SPD, or drop to 250 V under 643.3.2; the 1 MΩ minimum still applies |
| 4 | Polarity, including the supply | Polarity Testing Explained: Checks, Methods and EICR Codes |
| 5 | Zs at each accessible socket and at least one point on every other circuit | Compare against Maximum Zs Values BS 7671: Tables, 80% Rule and Ze |
| 6 | Prospective fault current at the board | Record the higher of PSCC and PEFC |
| 7 | Every RCD and RCBO | Instrument test at rated residual current, trip within 300 ms, plus the test button |
Table 41.1 disconnection times still govern: 0.4 s on TN and 0.2 s on TT for final circuits up to 63 A with sockets or 32 A without. If a Zs is over the limit, work through High Zs Readings: Causes, Checks and How to Fix Them before signing. RCD testing under the current rules is covered in RCD Testing Explained: Types, Test Currents and Trip Times, and the columns in How to Fill In a Schedule of Test Results, Column by Column.
What goes wrong on board-change certificates?
| Mistake | Why it matters | Fix |
|---|---|---|
| Minor Works issued instead of an EIC | Wrong document; fails assessment | Always an EIC |
| Extent reads "new consumer unit" only | Implies you certified the whole installation | State that existing circuits were reconnected, not renewed |
| Comments on existing installation left blank | No record of inherited defects | List them, or write "none apparent" |
| Schedule shows only Zs and RCD times | Dead tests not evidenced | Record continuity, IR and polarity per circuit |
| Insulation resistance shown as one figure with no note | Reader cannot tell what was tested | Note "whole installation" or give per-circuit values |
| Disconnected circuit not recorded | Client reconnects it later | Record, label and write to the client |
| Edition and amendment not stated | Ambiguous during a transition | Name the edition you worked to |
On the last point: BS 7671:2018+A4:2026 was published on 15 April 2026 and Amendment 2 is withdrawn on 15 October 2026. There is no legal duty to upgrade the rest of the installation to the current edition, but the Building Regulations require your work to leave it no worse than before.
How Certio helps
Certio produces the EICR, EIC, Minor Works certificate and PAT records on the BS 7671 model forms and turns them into branded PDFs. Photograph the consumer unit and the circuit schedule drafts itself; point the phone camera at a Megger MFT-X1 and the reading goes straight into the schedule of test results, or dictate it while your hands stay on the probes. Suggested observation wording with the regulation reference is there for you to check and confirm. The judgement stays yours; the typing goes. Starter is free for 7 days, then £4.99 a month.