Most domestic EICRs now start at a smart meter, and a great many of those supplies have no isolator between the meter and the consumer unit. Neither fact is a defect in the installation. BS 7671 requires a main switch at the origin, and Regulation 462.1.201 makes that the linked switch or circuit breaker in the consumer unit, not a separate isolator after the meter. What the missing isolator does affect is how you test safely, what you can measure, and how you write up the supply section. This guide covers that, along with meter tails, cut-out defects, and the smart meter behaviours that confuse readings.
- The consumer unit main switch is the required means of isolation at the origin; a separate meter isolator is helpful but not a BS 7671 requirement, so its absence is a limitation, not a code.
- The cut-out and service cable belong to the DNO; the meter, its seals and the tails up to the isolator belong to the supplier or meter operator. Report faults to the right party and record that you did.
- A smart meter's remote disconnect contactor is not a means of isolation for the electrician.
- 25 mm² tails are the norm for a 100 A cut-out fuse; 16 mm² tails carry about 87 A and are usually a C3 unless there is heat damage or a heavy load.
- Ze measured without disconnecting the earthing conductor must be recorded as measured with parallel paths and the limitation stated.
- Exposed live parts at a cut-out or meter are a C1 whoever owns them; record the danger, make it safe as far as you can, and report it.
Who owns what at the intake?
The intake is three pieces of equipment with three owners. The service cable, cut-out and cut-out fuse are the distributor's under the Electricity Safety, Quality and Continuity Regulations 2002 (ESQCR); the DNO is responsible for their condition and for the seals. The meter and, where fitted by the supplier, the isolator and the tails between meter and isolator belong to the supplier or its meter operator. Everything from the isolator, or from the meter output terminals where there is no isolator, to the consumer unit is the consumer's installation and is what the EICR covers.
This matters on the report because the EICR is a report on the installation, not on the distributor's equipment. Regulation 644.1.2 in the current edition requires the report to identify the extent of the installation covered and any limitations. Defects in the cut-out or meter still get recorded, because the inspector cannot ignore a danger, but the correct action for a cracked cut-out is a call to the DNO's emergency line and a note on the report, not a quotation to replace it.
A brief map of the intake:
| Item | Owner | Fault reported to | Typical EICR treatment |
|---|---|---|---|
| Service cable, cut-out, cut-out fuse, DNO seals | Distribution network operator | DNO emergency number | Record and report; C1 if live parts exposed |
| Meter, meter seals, tails meter-to-isolator | Supplier or meter operator | Supplier | Record and report; note as outside the installation |
| Isolator (where supplier-fitted) | Supplier | Supplier | Note presence; not part of the installation |
| Tails isolator-to-consumer unit, main earthing conductor, main bonding | Consumer | Consumer or landlord | Inspect, test and code as normal |
Is a missing isolator a defect?
No. The confusion comes from the practical wish for one, not from the regulations. BS 7671 requires a means of isolation at the origin under Regulation 132.15.201 and 462.1.201, and the consumer unit main switch satisfies that. An isolator between meter and consumer unit is recommended by the ENA and by most DNOs so that the consumer unit can be replaced without withdrawing the cut-out fuse, and many suppliers now fit one free when they exchange a meter, but nothing in BS 7671 makes it mandatory.
On the EICR, a supply with no isolator is written up under limitations rather than observations. The standard wording is along the lines of "No isolator fitted between meter and consumer unit; installation could not be isolated at the origin without withdrawing the cut-out fuse; Ze measured with earthing conductor connected". It is not a C3, because the installation does not depart from BS 7671. Where a consumer unit change is being quoted, the sensible advice to the customer is to have the supplier fit an isolator first, and that note can go in the recommendations rather than as a coded observation.
Withdrawing the cut-out fuse is a separate question. The seal belongs to the DNO and ESQCR Regulation 25 makes interference with distributor equipment an offence. In practice several DNOs allow electricians who are registered with a competent person scheme to remove the fuse for the duration of the work and then report it so a new seal can be fitted; the schemes and the requirements differ between network areas, so check your own DNO's current policy in writing. Where no such scheme applies, book the DNO to remove the fuse or the supplier to fit an isolator, and plan the EICR accordingly.
What does a smart meter change for the inspector?
A SMETS2 smart meter contains a supply contactor that the supplier can open remotely, for example on a prepayment cut-off or a change of tenancy. That contactor is a load switch under the supplier's control. It is not a means of isolation for you: you cannot lock it off, prove it, or rely on it staying open, and it does not meet the requirements of Regulation 462 or Section 537. Everything upstream of the consumer unit main switch is treated as live.
Smart meters also introduce a few behaviours that catch inspectors out. The load switch can open under a supplier command during your test, which looks like a supply failure; if the customer is on a prepayment tariff with a low balance this happens more than you would expect. Some meters take a moment to reconnect after the contactor closes. Some dual-rate meters switch tariff registers through a relay that clicks audibly and can be mistaken for a loose connection. None of this affects the installation, but it is worth knowing before you diagnose a fault that is not there.
The meter tails are where real observations live. For a 100 A cut-out fuse the expected tails are 25 mm² double-insulated single-core cable, rated about 114 A clipped direct from Table 4D1A for 70 °C thermoplastic singles. 16 mm² tails are rated about 87 A in the same configuration, which does not satisfy Regulation 433.1.1 against a 100 A fuse on the face of it. Whether that is a C2 or a C3 depends on the actual conditions: the DNO fuse rating (many older cut-outs carry 60 A or 80 A fuses), the maximum demand of the property, and any signs of overheating. Electrical Safety First Best Practice Guide 4 leaves this to the inspector's judgement. My practice is C3 where the tails are cool, undamaged and the load is modest, and C2 where there is discolouration, a large electric shower or EV charger, or the fuse is confirmed at 100 A with a heavy demand.
Other tails observations that recur: tails run without mechanical protection across a cellar or garage wall (C3, or C2 if the sheath is damaged), tails longer than the supplier's limit of about 3 m without their own fuse protection (C3, with a note that the DNO's requirement is not a BS 7671 regulation), and green/yellow sleeving used on the neutral tail of an older installation (C3 for identification under Regulation 514.3.1). Meter tails with no earth sleeving at all are not an issue because tails have no cpc; the main earthing conductor is a separate 16 mm² conductor from the cut-out or earth block to the main earthing terminal, and that one is inspected under Regulation 542.3.
How do I measure Ze and PFC without an isolator?
Ze is defined as the external earth fault loop impedance measured with the installation's main earthing conductor disconnected, so that parallel paths through bonded pipework do not flatter the reading. Disconnecting that conductor requires the installation to be isolated, and without an isolator or the fuse out you cannot do that safely. Guidance Note 3 accepts a Ze reading taken with the earthing conductor connected provided it is recorded as such and the limitation is stated. The value will be lower than the true Ze, which is unconservative for the disconnection-time check, so if the measured figure is close to the maximum for the supply type (0.35 Ω for TN-C-S, 0.8 Ω for TN-S, 21 Ω for a typical TT) say so and flag it. See What is Ze? External earth fault loop impedance.
Prospective fault current is measured live at the origin between line and neutral and between line and earth, and the higher of the two is recorded. That test is unaffected by the isolator question. If your tester reports 16 kA on a domestic supply, the reading is almost certainly the meter's low impedance rather than a reality; a typical TN-C-S domestic PFC is 1 to 3 kA and the 6 kA breaking capacity of a domestic consumer unit is adequate under the Regulation 536.4.201 conditional short-circuit rating. See What is prospective fault current (PFC)? Explained.
What supply defects are coded on an EICR?
The table shows the common intake findings and how they are usually treated, following Best Practice Guide 4 and NICEIC guidance. As always, the code is the inspector's decision for the installation in front of them.
| Finding | Owner | Usual code | Notes |
|---|---|---|---|
| Cracked cut-out with live parts accessible | DNO | C1 | Make safe as far as possible, call DNO emergency line, record on report |
| Scorching or heat damage at cut-out or meter terminals | DNO or supplier | C2 (C1 if live parts exposed) | Report to owner of the equipment |
| No isolator between meter and consumer unit | n/a | Limitation, no code | Not a BS 7671 requirement |
| 16 mm² tails on 100 A fuse, no heat damage | Consumer | C3 | C2 if overloaded or damaged |
| Main earthing conductor undersized or missing | Consumer | C2 (C1 if no earth at all with exposed metalwork) | Regulation 542.3 and Table 54.1 |
| Main bonding to water or gas absent on TN-C-S | Consumer | C2 | Regulation 411.3.1.2 |
| Tails unsheathed or unprotected in a garage | Consumer | C3, or C2 if damaged | Regulation 522 |
| DNO earth terminal present but earthing type unconfirmed | DNO | FI | Request confirmation from DNO before certifying TN-C-S |
The last row matters more than it looks. If the earthing conductor is connected to the cut-out but you cannot confirm whether the DNO has provided a TN-C-S or TN-S earth, a Ze reading in the 0.2 to 0.4 Ω range does not tell you which. Record the earthing arrangement as the DNO has declared it, or as unconfirmed with an FI, rather than guessing. For more on the coding framework see EICR observation codes explained: C1, C2, C3 and FI and on the general process How to Do an EICR Step by Step: Inspector's Workflow.
How Certio helps
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