Unsatisfactory Is a Verdict on Four Letters
The report is nine pages and the only word anybody reads sits in a box on page one. By the time the landlord has finished reading it there is a quotation in the inbox for four and a half thousand pounds, arriving the same afternoon from the firm that did the inspection, and the two documents are already being treated as one transaction. They are not. The word in the box is generated mechanically: a single C1, a single C2 or a single FI anywhere in the observations produces an overall assessment of unsatisfactory, and fourteen C3s and nothing else produces a satisfactory report on an installation that is visibly older and shabbier. The verdict measures whether a line was crossed, not how far.
So the useful reading order is backwards. Go to the schedule of observations, copy the numbered items into a list of your own with their codes beside them, and count the codes before reading a word of what they say. That count is the shape of the job: the C1s and C2s are the work, the FIs are unpriced unknowns, and the C3s are a shopping list you are free to ignore. Then ask for the quotation to be reissued line-referenced to those observation numbers. Every honest remedial answers a numbered item. A line in a quote that maps to no observation is not a remedial, whatever else it may be worth doing.
Before any of that, read the box nobody reads: extent and limitations. BS 7671 Chapter 65 requires the extent of a periodic inspection and any limitations on it to be agreed with the person ordering the report and recorded on the form — which is why a domestic report usually records a percentage sample of accessories, no access to a loft, and no floors lifted. That box lists what was never looked at, and a clean sheet over an area the inspector could not reach is worth what it cost. It matters most to a buyer holding a report the seller commissioned, who agreed none of those limitations and was not there when they were set.
C1, C2, C3 and FI — Only Three of Them Are Work
The four codes are not a severity scale with money attached at every step. C1 asserts that danger is present now and somebody can be hurt by touching what is already there. C2 asserts potential danger — the installation is safe while nothing else happens, and unsafe as soon as one further thing does: a fault occurs, a cover comes off, a person makes contact with something that is live only because a protective measure is missing. C3 asserts nothing about danger at all. It records that the installation would be better if something were improved, and it is the inspector's opinion offered as advice.
Code allocation is judgement exercised against a published reference, not a lookup. The reference is Electrical Safety First's Best Practice Guide 4, Electrical Installation Condition Reporting: Classification Codes for Domestic and Similar Electrical Installations, and naming it is how you reopen a code rather than argue about it in the abstract. Two competent inspectors can code one defect differently and both be defensible; what is not defensible is a C2 with no stated reasoning, and asking for that reasoning is a normal professional request.
| Code | The assertion | What it obliges |
|---|---|---|
| C1 — danger present | Risk of injury from the installation as it stands, without anything further happening | Made safe during the inspection visit, normally by isolation. If a C1 is on your report and nothing was made safe that day, ask why before you ask the price |
| C2 — potentially dangerous | Safe now, unsafe on one further event: a fault, a removed cover, a person reaching something a missing protective measure would have covered | Remedial work. This is the bulk of the priced job and the bulk of the legitimate argument about scope |
| FI — further investigation required | The inspector found something they could not resolve inside the agreed extent, and is declining to guess | Investigation, not repair. It cannot honestly be quoted as a fixed sum until it is done |
| C3 — improvement recommended | No danger asserted. The installation would be better with this, usually measured against the current edition | Nothing. It cannot make a report unsatisfactory and it obliges no one. Price it separately and decide on its merits |
Twenty-Eight Days, and Whose Twenty-Eight Days They Are
For a landlord letting in England the clock is statutory and it is shorter than it looks. The Electrical Safety Standards in the Private Rented Sector (England) Regulations 2020 require the installation to be inspected and tested at intervals of no more than five years, and where the report requires further investigative or remedial work, that work must be completed within twenty-eight days — or within a shorter period if the report specifies one — running from the date of the inspection and testing. Not from the date the report landed in your inbox. An inspector who tests on the second and issues on the ninth has already spent a quarter of your window on typing.
Completion is not the end of the obligation either. The regulations require written confirmation from whoever did the work that it is complete and that the standards are now met, and that confirmation, with a copy of the original report, has to reach the tenant and the local housing authority within twenty-eight days of the work finishing. A local housing authority with reasonable grounds to believe the duty has been breached can serve a remedial notice, arrange the work itself and recover the cost, and impose a financial penalty of up to thirty thousand pounds. The penalty attaches to the failure to act, which is why the paper trail matters as much as the wiring.
A buyer is in a completely different position and is routinely given the landlord's advice by mistake. Nobody buying a house is under a deadline; the report is leverage, and its codes are the vocabulary for a price reduction or a retention rather than a schedule of enforced work. The one case where the clock catches a buyer is a purchase for letting, and even then it does not start on the seller's report — it starts on the one the new landlord obtains, against limitations they agreed, before the property is occupied.
The rest of the United Kingdom reaches a similar duty by different routes: the repairing standard under the Housing (Scotland) Act 2006, the Renting Homes (Wales) Act 2016 with the fitness-for-human-habitation regulations made under it, and the Private Tenancies Act (Northern Ireland) 2022. Read whichever applies rather than assuming the English twenty-eight days travels unchanged across a border. Outside housing, a commercial installation answers to the Electricity at Work Regulations 1989, which sets no interval at all and instead requires systems to be maintained so as to prevent danger — a duty a periodic report discharges rather than satisfies on a timetable.
One consequence of the clock is worth acting on the day the report lands: it does not pause while scope is argued about. Instruct the C1s and the uncontested C2s immediately as their own order and run the dispute alongside. That costs a second visit, and it is far cheaper than a penalty notice about the three items nobody could agree on.
An Installation Built to an Older Edition Is Not Automatically Unsafe
The model report form in Appendix 6 of BS 7671 states the principle on its own face: an installation designed to an earlier edition that does not fully comply with the current one is not necessarily unsafe or in need of upgrading. Codes are allocated by looking at today's requirements, but a departure from today's requirements is only a C1 or a C2 if the departure is itself a hazard. Everything else is a C3, and a C3 is a suggestion.
That distinction disposes of a large share of the observations that alarm people. A plastic consumer unit installed before Regulation 421.1.201 required non-combustible enclosures in domestic premises is a plastic consumer unit, not a fire. Arc fault detection devices became a requirement only for a short list of higher-risk premises under Amendment 2 to the 18th Edition and a recommendation elsewhere, so their absence in an ordinary flat is not a defect in that flat. North American practice is non-retroactive in the same way: the National Electrical Code governs new work, it takes Article 80 where a jurisdiction has adopted it for an authority having jurisdiction to compel changes to something already installed, and NFPA 73 exists specifically for inspecting existing dwellings rather than for building them.
Where an old installation stops being merely old is when something happened after it was built. The 1994 radial with no RCD becomes an argument the moment a socket on it feeds an extension lead into the garden, because Regulation 411.3.3 exists for precisely that use. A cable buried thirty millimetres deep in a plastered wall is a genuine C2 not because of its age but because Regulations 522.6.202 and 522.6.203 exist and the chase was cut for a socket added last year. Read every observation against that question — is this defect original, or did somebody create it since — because the answer usually decides both the code and who ought to be paying.
Re-Deriving the Observation That Says a Cable Is Undersized
A recurring C2 on domestic reports reads roughly as conductors not suitable for the protective device due to installation conditions, and it appears wherever a cable has been found buried in loft quilt, bunched with five others in a joist notch, or run through the back of an airing cupboard. It is one of the few observations that is pure arithmetic, which means it is one of the few you can check without going near the installation. The claim is that the cable's tabulated current-carrying capacity, once the correction factors for the conditions are applied, comes out below the rating of the device in front of it.
There are up to three multipliers in that claim and they are not equally solid. The ambient correction and the grouping adjustment come from tables and are hard to dispute. The insulation factor is the one worth examining: BS 7671 Table 52.2 derates a cable enclosed in thermal insulation, and one totally surrounded over half a metre or more attracts a factor of 0.5 — half the capacity, gone. But that factor applies to what the cable actually does, and an inspector who watched one length disappear under quilt may have charged the full penalty to a circuit clipped direct for the other twenty metres. If the worst three hundred millimetres are the problem, the honest remedial is to lift the cable clear of the insulation: a morning with a torch, not a rewire.
When the arithmetic genuinely fails, look at both ends of the mismatch before accepting the expensive one. A circuit whose conductors derate to twenty-four amperes under a thirty-two ampere breaker can be corrected by changing the cable or by changing the device, and changing the device costs a fraction of changing the cable. Whether that is acceptable depends entirely on what the circuit serves — dropping a kitchen ring to a twenty ampere device is not a remedial, it is a new defect waiting to be coded next time — but on a lightly loaded upstairs circuit it is frequently the correct answer, and it is almost never the one on the quote.
Two of the three multipliers behind that observation live here — the ambient correction and the grouping adjustment. The fields are labelled to the NEC tables, but nothing is looked up for you: type in the tabulated capacity for the reference method the cable is actually installed by, and the Ca and Cg factors from BS 7671 Appendix 4, and the arithmetic is the same. Where part of the run also sits in insulation, apply the Table 52.2 factor to the result by hand, then compare what survives against the rating of the device that is actually fitted.
The conductor's tabulated ampacity before any correction or adjustment factors are applied.
The multiplier for the ambient temperature the conductor will actually operate in, from the applicable NEC temperature correction table.
The multiplier for the number of current-carrying conductors bundled together in the same raceway or cable.
Derated conductor ampacity
91.5 A
Verify both correction factors directly against the current NEC tables for your specific ambient temperature and number of current-carrying conductors — this calculator applies factors you supply, it does not look them up for you.
They open the calculator with your figures already in it
Feeder Conductor Ampacity Derating Calculator: 91.52 A — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Add the equipment this sizes
This result is a specification — 91.5 A — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
What this calculation does not cover
- Derating and terminations are two separate ceilings and the lower one governs. NEC 110.14(C) holds the conductor to the 60°C or 75°C column for whatever the breaker and lugs are listed at, so a run derated down from the 90°C column can still not be used above its 75°C table value — the number this page returns may legitimately be higher than the ampacity you are allowed to claim.
- The adjustment factor you type depends on a conductor count this page cannot verify. Equipment grounding conductors and the neutral of a balanced circuit are not current-carrying, while the neutral of a three-phase, four-wire wye feeding significant nonlinear load is — reclassifying one conductor can drop you a whole band in Table 310.15(C)(1). The adjustment also does not apply at all through a nipple of 24 in (610 mm) or less.
- A derated ampacity proves nothing by itself. It still has to cover the load it serves at 125 percent of the continuous portion, sit correctly with the overcurrent device protecting it, and survive a voltage drop check over the length of the run. This page stops one step before all three.
The Circuit Somebody Says Is Overloaded
Overload observations are different in kind from the one above, because they are about what has been plugged in rather than what was installed. The usual case is a kitchen that has quietly acquired a second oven, an induction hob and a tumble dryer over fifteen years, all landing on wiring that was laid out for a kettle and a toaster. Nothing in the fabric has changed and nothing has been done badly; the household simply outgrew the circuit. That is a real observation and it is also the one most often used to justify work far larger than it needs.
Put the connected load against the device and the outcome splits three ways, each with a different price. If the sum comes in comfortably under, the observation was a judgement about a busy-looking kitchen and can be discussed. If it is marginal, the remedial is one dedicated circuit for one appliance and the rest of the kitchen stops being the problem. If it is badly over, the remedial is that circuit plus a position in the board to protect it from — which is where the whole quotation turns, and which the next section is about.
Total what is genuinely connected to the circuit the observation names and put it against the device protecting it. This runner is built to the North American continuous-load rule and offers 120 or 240 volts on a 15 to 50 ampere breaker, so a British 32 ampere circuit at 230 volts has no exact setting here: take the nearest pair and read the percentage of continuous capacity rather than the amperage. That percentage — not the observation's adjective — is the difference between a conversation and a new circuit.
The amp rating printed on the breaker in your panel.
Most household outlets in North America are 120V; large appliances (dryers, ranges, EV chargers) are often 240V.
The sum of the wattage of everything plugged into this circuit at once.
Current draw
10 A
- Total connected load
- 1,200 W
- Safe continuous limit (80% rule)
- 16 A
- Safe continuous limit
- 1,920 W
- % of safe continuous capacity used
- 62.5 %
They open the calculator with your figures already in it
Electrical Circuit Load Calculator: 10 A — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Add the equipment this sizes
This result is a specification — 10 A — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
What this calculation does not cover
- ONE circuit, not the panel. Whether the service and the panel can carry everything together is a separate calculation under the code's demand-factor rules, and a house full of individually compliant circuits can still overload its supply.
- Says nothing about the WIRE. Conductor ampacity is set by the conductor, its insulation, the ambient temperature and how many current-carrying conductors share a raceway — a breaker rating does not guarantee the cable behind it, and a correctly sized breaker on undersized cable is the dangerous combination.
- Voltage drop over the run is not checked here. A circuit inside its current limit can still deliver too little voltage at the far end, which is a separate calculation.
- Motor and compressor loads draw several times their running current at start-up. Nameplate watts describe the running condition and understate what the breaker sees on a cold morning.
- The 80% figure applies to CONTINUOUS loads — three hours or more at full draw. A load that is genuinely intermittent may use more of the breaker's rating, and which of the two a given appliance is can be a judgement.
Code thresholds this tool can check
Code thresholds this tool can check
Checked for United States. Each check below names the body that published the limit it uses. Switching market re-runs them. This is not a code review and has no official standing.
These checks cover only the specific numeric limits listed below. They are not a complete code review: fire separation, egress, structural capacity and accessibility provisions are outside their scope, and only the handful of local amendments offered in the selector are modelled — your municipality may have others. Passing every check here does not make a design compliant. Final approval rests with your local building authority.
Readings Are Evidence, and the Schedule Is Where You Audit the Inspector
The schedule of circuit details and test results is the part a homeowner skips and the part a second opinion starts from, because measured numbers can be checked against published limits without anybody returning to the property. Three of them do most of the work, and each has a characteristic way of being read wrongly.
Earth fault loop impedance is the first. The maximum values in Tables 41.2 to 41.4 of BS 7671 assume the conductor sitting at its normal operating temperature, and a test carried out on a cold installation reads lower than the circuit will behave in service — which is why the IET's guidance applies a correction, commonly taken as a factor of 0.8 on the tabulated figure, before a measured value is called a pass. A thirty-two ampere Type B circuit breaker has a tabulated maximum of 1.37 ohms for a 0.4 second disconnection time. Measured at ambient you want it comfortably under about 1.10 ohms, so a recorded 1.2 ohms is not a pass merely because it is under 1.37, and a report that has treated it as one has a systematic error in it rather than a single mistake.
Insulation resistance is the second, and it is the reading most often over-reacted to. Table 64 of BS 7671 sets one megohm as the minimum on a 500 volt direct-current test for ordinary circuits, while IET Guidance Note 3 advises investigating anything below two megohms even though it has technically passed. A circuit reading 0.4 megohms has failed, but the cause is far more often a single wet lamp holder, an immersion element or one damaged accessory than a distributed failure of the wiring, and an FI is the appropriate code. Accepting a rewire quote off a low insulation reading, before anybody has split the circuit and re-tested each half, is the single most expensive mistake available on these reports.
Prospective fault current is the third and the quietest. Recorded at the origin, it wants comparing against the breaking capacity marked on the devices — BS EN 60898-1 breakers are commonly rated at six kiloamperes, in an assembly to BS EN 61439-3 with a rating of its own. Where the recorded figure exceeds what is marked and no upstream device provides a conditional rating, that is a legitimate observation about equipment that cannot interrupt what the network can deliver.
| Reading | Where the limit comes from | What a genuine failure usually means |
|---|---|---|
| Earth fault loop impedance, Zs | BS 7671 Tables 41.2 to 41.4, corrected for the conductor being at ambient rather than operating temperature | A protective device that will not disconnect in time. Sometimes a loose termination and a retest; sometimes a conductor size or a supply earthing question |
| Insulation resistance | BS 7671 Table 64 — one megohm at 500 V DC — with Guidance Note 3 advising investigation below two | Almost always one accessory, one appliance or one damp point. Split the circuit and retest before anyone prices cable |
| Prospective fault current, Ipf | The breaking capacity marked on the devices, to BS EN 60898-1, and the assembly rating to BS EN 61439-3 | Devices that cannot clear the fault the supply can deliver. Resolved with equipment or an upstream device, not with rewiring |
| Earth electrode resistance, RA | BS 7671 Regulation 411.5.3, with stability rather than the arithmetic being the practical constraint | Rarely a failure on the arithmetic alone. Read the next section before agreeing to buy a second rod |
The Electrode Reading, and Whether a Second Rod Would Move It
On a property with its own earth electrode — most often a rural site with no distributor earth on offer — the report records an electrode resistance, and that number is misread in both directions. Regulation 411.5.3 of BS 7671 requires the product of the electrode resistance and the residual operating current of the protective device not to exceed fifty volts, which a thirty milliampere device satisfies at values so high they are meaningless in practice. The real constraint is not the arithmetic but stability: an electrode of a few hundred ohms is measuring the moisture in the ground on the day it was tested, and the IET's guidance treats values above about two hundred ohms as unlikely to hold. So a recorded one hundred and eighty ohms is a figure to think about, not automatically a failure, and the month it was measured in belongs beside it — a reading taken after a wet March is the best that ground will ever give.
Where that becomes a pricing question is the line item that says an additional earth electrode. It is a cheap-sounding remedial that frequently achieves nothing, because two rods driven a spade's width apart behave electrically as one slightly fatter rod, and diameter barely moves the number. Separation of at least the driven length is what turns a second rod into a second electrode, and on a site where the first rod refused at a metre against rock the second will refuse at the same depth for the same reason. Work out what the ground can give before buying an attempt at it: depth is the term that dominates, and if the depth is not available the honest answer is a different electrode arrangement or a conversation with the distributor about an earthing terminal, not more of the same rod.
Everything about how the reading is actually taken — the three-lead method, the ways a measurement lies, and the bonding argument that sits behind the whole earthing arrangement — belongs to the earthing and bonding guide on this site, which owns it properly. What belongs here is narrower: whether the number written on this report justifies the line written on this quote.
Enter the resistivity of the ground the property sits on and the depth a rod could realistically reach there, then push the length up and watch how slowly the ohms come down. That curve is the argument against paying for a second rod on a site that will not take a longer one.
How strongly the surrounding soil resists electrical current flow.
The length of the ground rod actually driven into the earth.
The rod's outer diameter.
Estimated ground rod resistance
39.9 Ω
Soil resistivity varies significantly with moisture, temperature, and composition — use a field-measured value (e.g. Wenner four-pin test) for your actual site rather than an assumed value. NEC 250.53(A)(2) requires a single rod to test at 25Ω or less, or a second rod must be added; this calculator estimates the resistance, it does not replace an actual field measurement.
They open the calculator with your figures already in it
Isolated Ground Rod Earth Resistance Calculator (Dwight's Formula): 39.89 Ω — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Add the equipment this sizes
This result is a specification — 39.9 Ω — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
What this calculation does not cover
- Dwight's formula assumes one uniform soil for the full depth of the rod, and real ground is layered. A wet clay skin over dry sand, or two feet of topsoil over rock, cannot be reduced to a single resistivity — and if the rod refuses on rock at 1.2 m then the length in the formula is 1.2 m, not the 2.4 m of steel that was bought. A Wenner traverse at several pin spacings reveals the profile; one number conceals it, and the error runs to a factor rather than a percentage.
- Resistivity is seasonal, and the shallow soil moves the most. It climbs steeply as ground dries and again as it freezes, where it can rise by an order of magnitude, so the upper metre — the part that dries and freezes — contributes least at exactly the times it is needed. A rod that measures 20 Ω after spring rain can be well past the 25 Ω threshold in February or in a drought, which is why driving below the frost line does far more than diameter ever will.
- One isolated rod. Add a second and the resistance does not halve, because the two current fields overlap — set them closer than the driven length apart and the pair behaves more like a single larger electrode than like two in parallel, which is the reason a minimum separation exists at all. Nor does this see the rest of the electrode system: a concrete-encased electrode, a metal water service or bonded building steel sits in parallel with the rod and usually dominates whatever a fall-of-potential or clamp-on test actually reads.
- A low rod resistance does not clear a fault. On a grounded AC system the fault current returns to the source along the equipment grounding conductor, and the earth is explicitly not permitted to serve as that path — a flawless 5 Ω rod will not operate a breaker. The rod is there for lightning, for static and for holding the system's voltage reference, so ohms in the ground are no substitute for a continuous low-impedance bonded return.
FI Is the Line That Destroys a Fixed Price
Further investigation is the honest code and the awkward one. It says the inspector found something they could not resolve inside the agreed extent — a circuit going somewhere the sample did not reach, a reading that contradicts the schematic, a spur with no discoverable origin — and that they will not guess at it. An FI is not a small C2 or a large C3. It is an unknown, and an unknown cannot be priced.
Which means any quotation that puts a firm figure against an FI has done one of two things: guessed, or quietly decided the answer in advance and priced the remedy it expects to sell. Neither is what you asked for. Instruct an FI as time against a stated cap with an instruction to stop and report, and treat whatever it finds as a new item to be coded and priced on its own. Under the private rented sector regulations the investigation itself counts as the work that has to happen inside the window, so instructing it early matters more than instructing it cheaply.
- Ask the inspector, in writing, what they saw that they could not resolve and what they suspect — the FI wording on the form is rarely the whole thought.
- Instruct the investigation as hours at a stated rate with a cap, not as a lump.
- Require it to stop at the cap and report, rather than continuing into remedial work it has just discovered a reason for.
- Have the finding written up as a new observation with its own code before anything is priced against it.
- Where the FI concerns a circuit nobody can trace, agree in advance whether the answer may be to disconnect and abandon it rather than to prove it.
Whether the Remedials Fit in the Board You Already Have
This is the fork that decides the size of the bill, and it is usually settled before anybody looks properly. A clear majority of C2s on domestic reports resolve to one remedy: residual current protection on circuits that do not have it. In a board with spare positions and a device range still in production, that is a per-circuit device change and a retest — hours, not days. In a board that is full, obsolete or a rewireable fuse box, the same observations force a consumer unit replacement, which drags the tails, the main earthing conductor, the bonding and the notification along with it.
Count positions in modules rather than in ways, because that is the unit the enclosure actually sells. A board described as ten way with eight ways occupied has two free positions, and eight residual current breakers with overload protection need eight positions, not two. Modern ranges mostly make those devices one module wide, but not all do, and a surge protective device the specifier wants to add takes two more. The count is arithmetic and it takes a minute, and it is the difference between a quotation you can sanity-check and one you have to trust.
There is a legitimate version of the board change that has nothing to do with the observations at all: devices for the existing range are no longer manufactured, so the cheap per-circuit remedial does not exist as a purchasable component. That is a real reason and deserves stating as one rather than being blurred into the safety argument. Remember too that in England and Wales a consumer unit replacement is notifiable under Approved Document P, so it carries a certificate and a notification that a socket-front swap does not. The changeover itself, hour by hour, is its own guide on this site.
Put in the positions the existing enclosure has and what is presently in them, then add the devices the observations force. If the answer is negative before the surge protection is counted, the quotation in front of you is a board change whether or not it says so.
The total number of breaker spaces the panel provides.
Each single-pole breaker occupies one panel slot.
Each double-pole breaker occupies two panel slots.
Available panel slots remaining
10 slots
The breakers entered need 30 slots against the 40 this panel has. Being inside the rating on this one check settles nothing about the rest of the circuit — the conductors, the overcurrent device, and the work as installed are all outside it.
- Slots used
- 30 slots
They open the calculator with your figures already in it
Electrical Panel Circuit Directory Slot Calculator: 10 slots — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
What this calculation does not cover
- Spaces left is not capacity left. What may be added to a panel is governed by its bus and main breaker rating measured against a calculated load with demand factors applied, not by empty positions. A 100 A panel with twelve free spaces may have no room for a range or a heat pump at all, and filling the spaces anyway is exactly how a bus gets overloaded while every breaker in it holds.
- There is no place here for a three-pole breaker. In a three-phase panel a 3-pole device fills three spaces, and entering it as a double-pole loses one space every time - on a commercial schedule that is several positions gone by the time the count matters. The panel also has a fixed number of positions per phase, which decides where a three-phase load can physically go, not just whether it fits.
- Breaker spaces are not the only thing a panel runs out of. Every grounded conductor needs its own terminal, since NEC 408.41 permits one neutral per terminal, and equipment grounds, AFCI and GFCI pigtails and multiwire circuits eat bar holes faster than they eat positions. A panel with four spaces free and a full neutral bar needs an added bar kit, and the wire bending space in a crowded gutter is a code dimension in its own right.
When the Quote Stops Being About the Report
Somewhere between the observation schedule and the covering letter, three C2s about missing residual current protection become a proposal for a full rewire. Sometimes that is the honest answer — a board change opens up the tails and the earthing arrangement, an installation with cloth-covered conductors will fail its insulation test in stages over the next five years, and doing it once is genuinely cheaper than doing it four times. Sometimes it is a condition report being used as a door-opener. The two look identical on paper and are separated by one question: which numbered observation does this line answer?
A rewire answers all of them, which is not the same as answering any of them. Ask for the priced schedule twice — once as the minimum work that clears the unsatisfactory verdict, and once as the work the contractor would recommend — and treat the difference as a proposal to be considered on its own merits rather than as a deadline. The first schedule is what the regulations oblige. The second may still be the better purchase, and it is much easier to agree to when it is not disguised as compulsory.
Where a board change is genuinely in scope, put the dwelling's assessed demand on the table while the argument is still open. The main switch, the tails, the main earthing conductor and the distributor's cut-out fuse all have to agree with each other, and a board change that uncovers sixteen square millimetre tails on a hundred ampere cut-out grows for a defensible reason rather than an opportunistic one. Whether the incoming supply itself needs raising is a separate application to a separate organisation and has its own guide here; what belongs on this page is knowing, before the quote arrives, whether the house is anywhere near that boundary.
Assemble a whole-dwelling demand figure on the property as it will be used, not as it was built, before agreeing that the existing service is too small. This runner uses the NFPA 70 Article 220 standard method — floor area, small-appliance and laundry circuits, fixed-appliance nameplate, then the demand factor — so treat what it returns as the worked shape of the calculation rather than as a British answer; a United Kingdom assessment runs the same assembly through the On-Site Guide diversity appendix. Either way, on most houses that produce alarming quotations the demand lands well inside the service already there.
The total livable floor area of the dwelling used for general lighting load.
20A kitchen/dining small-appliance circuits, each counted at 1500 VA.
Dedicated 20A laundry branch circuits, each counted at 1500 VA.
Sum of the nameplate VA for fixed appliances such as the water heater, range, oven, and dryer.
The nominal service voltage supplying the dwelling.
Estimated required service amperage
38 A
This is a SIMPLIFIED illustrative version of the NEC 220 standard method, omitting several real-world factors (HVAC load, EV chargers, largest motor load addition, optional calculation method). Fixed appliances are carried at 100% because this page takes a VA total and not a count; 220.53 permits 75% where four or more fastened-in-place appliances are present, and a range or a dryer has its own table (220.55, 220.54) that this does not apply. It is NOT a substitute for a complete NEC Article 220 load calculation performed by a licensed electrician, which determines your actual required service size and is required for permitting. Always round up to the next standard breaker/service size (100A, 125A, 150A, 200A) and consult your electrician.
- Total connected load (before demand factor)
- 13,030 VA
- General lighting and receptacles, after the 220.42 factor
- 5,110.5 VA
- Fixed appliances, at 100%
- 4,000 VA
- Demand load
- 9,110.5 VA
They open the calculator with your figures already in it
Home Electrical Service Panel Amperage Sizing Calculator: 37.96 A — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Add the equipment this sizes
This result is a specification — 38 A — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
What this calculation does not cover
- Amps are not spaces. This sizes the SERVICE and says nothing about the panel's physical capacity — a dwelling can sit comfortably inside 100 A of calculated demand and still need a new panel because every breaker position is taken, the busbar is rated below what is being added to it, or the enclosure will not accept the breaker type the new circuits require. Panels get replaced for spaces at least as often as for amperage.
- The amperage is where the rest of the sizing starts, not where it ends. Service-entrance conductors, the grounding electrode conductor, the meter base, the mast or lateral and the utility's own drop or transformer all follow from this number and none of them fall out of it — and a dwelling service gets its own conductor allowance under NEC 310.12 rather than the general ampacity table, so the wire for a 200 A house is not the wire that table would give it.
- One dwelling unit. A second unit on the same service, an ADU, or a detached garage or workshop on a feeder are not added by piling their loads into these boxes: a multifamily service runs through 220.84's own demand table, and a feeder to an outbuilding is calculated as its own load under 220.40. Stacking two dwellings into this page understates both of them.
The Paperwork That Actually Closes It
The commonest and most avoidable overspend at the end of all this is paying for a second full condition report to prove the remedials were done. That is not the document the regulations ask for and it is not the document a purchaser's solicitor needs. What closes a remedial is written confirmation from whoever carried out the work that it is complete and that the installation now meets the standards, accompanied by the certificate the work itself generates — an Electrical Installation Certificate where a new circuit or a new consumer unit was installed, a Minor Electrical Installation Works Certificate for work that added no new circuit. A fresh report costs more, restarts nothing useful, and reliably produces a new crop of C3s to worry about.
- Collect the completion confirmation and the certificate for each piece of work, not a replacement report.
- Check that every C1, C2 and FI on your original numbered list is accounted for by something in that pack.
- Where a C3 was declined, write down that it was declined and why, so the decision survives the next change of agent or owner.
- As a landlord in England, send the confirmation with the original report to the tenant and to the local housing authority inside twenty-eight days of the work finishing.
- File the schedule of test results with the certificates — the next inspector will retest against those figures, and a circuit that has drifted is far easier to argue about with a baseline.
- Diarise the next inspection from the date of the original testing, which is the date the interval runs from.
Turning a coded report into a schedule you can price
Work down this before asking anyone for a number. Each line either removes work from the job or tells you what a line on a quotation is really for, and the first three cost nothing but an hour with the report open.
- Codes counted before the observations are read — C1s and C2s are the job, FIs are unknowns, C3s are optional. The count is the shape of the work; the prose is the detail.
- Extent and limitations read first — Whatever was sampled, skipped or inaccessible was not inspected — and a buyer agreed none of it.
- Every quoted line mapped to an observation number — A line that answers no numbered item is a recommendation. It may still be worth buying; it is not a remedial.
- The arithmetic observations re-derived — Derating claims and overload claims can be checked from the report alone, without anybody revisiting the property.
- Failing test values traced to a cause, not to a remedy — Low insulation resistance is one accessory far more often than it is a rewire. Split the circuit and retest before pricing cable.
- Free positions in the existing board counted in modules — Device-level remedial or a whole consumer unit is the largest single fork in the price, and it is settled by a count.
- Each FI instructed as capped time with a stop-and-report — A fixed price against an unknown means somebody has already decided the answer without looking.
- Two schedules requested: the minimum that clears it, and the recommendation — Both may be reasonable. Only one of them is what the deadline obliges, and they should not arrive as a single number.
Opens the calculators above on one screen with the dimensions from this article already filled in. Quantities only — this site publishes no price list, because local prices vary too much to publish honestly.