Workspace Tools and Engineering Calculators

Household bill calculator and the Default Tariff Cap base

The household bill calculator turns a Default Tariff Cap level for the current quarter into a worked annual bill on a real meter. The Default Tariff Cap is the price ceiling Ofgem sets every three months under Standard Licence Condition 28AD of the Electricity and Gas Supply Licences. The Q1 2026-27 cap (April to June 2026) was announced on 25 February 2026 and sets the typical dual-fuel direct debit household at a published annual figure that becomes the base input.¹⁰ The cap covers the standing charge and the unit rate for both electricity and gas, separated by region. The calculator reads the four current numbers (electricity standing charge, electricity unit rate, gas standing charge, gas unit rate) and multiplies them through the reader's own annual usage in kilowatt-hours.

The mechanics are deliberately simple: annual cost equals annual usage times unit rate, plus 365 days times daily standing charge, plus 5 percent VAT applied to the total. Domestic electricity and domestic gas are both at 5 percent VAT under the Value Added Tax (Reduced Rate) (Energy-Saving Materials) Order, so the calculator applies it once at the end rather than per row. The published annual figure for the typical household assumes 2,700 kilowatt-hours of electricity and 11,500 kilowatt-hours of gas, which are the Ofgem Typical Domestic Consumption Values reset for 2026 and which the calculator pre-fills as the default.

Three practical notes sit next to the calculator so a reader knows what the result is and what it is not. The cap is a ceiling, not a tariff: a supplier may charge less, and in any month where wholesale costs are very low the standing charge can take a larger share of the bill than the unit rate. The cap excludes the Warm Home Discount and the policy-cost recoveries that sit inside the Renewables Obligation, the Feed-in Tariff, the Smart Export Guarantee and the Energy Company Obligation, all of which sit inside the unit rate already so the reader does not have to add them. The cap is uniform within an Ofgem region but not within a meter: a household on a tariff that is fixed or that is below the cap will not pay the calculator's figure, and the calculator says so on every result.

Hand off to: the bills route on the workspace for the policy context around the cap and the regional variation across the fourteen Ofgem electricity regions; the carbon intensity lookup below for the matched emissions reading on the same half-hour.

Carbon intensity lookup and the half-hour interval

The carbon intensity lookup reads the half-hour grid carbon factor in grams of carbon dioxide per kilowatt-hour from the NESO Carbon Intensity API. The API publishes the national factor and the fourteen regional factors on a public endpoint with no authentication.⁹ The endpoint serves both the actual factor for past intervals and a forecast for up to 48 hours ahead, on the same half-hour grid that the Balancing Mechanism Reporting Service uses for settlement. The lookup on this workspace reads the current interval and the last 24 hours, and shows the next 24 hours of forecast intervals alongside.

Two things about the published number make a difference for any reader doing emissions work. The factor is the carbon intensity of the marginal generation mix at the half-hour, weighted by the actual physical metered output of every fuel type on the grid (the carbonintensity.org.uk methodology paper sets out the per-fuel emissions factors). The factor is not the long-run average for the year, and it is not the consumed mix at the meter (which would include line losses and the import-export balance through the interconnectors). When a reader needs the consumed mix for a corporate carbon disclosure they should still use the Department for Energy Security and Net Zero conversion factors for greenhouse-gas reporting, which are the published annual values used in mandatory disclosures.

Three reading habits sit next to the carbon lookup. The first is to read the factor in context against the prior week so a single low or high reading does not stand alone. The second is to compare the national figure to the regional figure for the reader's own DNO area because regional figures differ by up to a factor of three between Scotland and South West. The third is to read the forecast 24 hours ahead before scheduling any large flexible load (an EV charging session, a heat pump pre-heat, a domestic battery charge) so that the timing decision is made against the half-hour the system will actually run in, not against the half-hour the reader started thinking about it.

Hand off to: the live generation dashboard below for the physical fuel mix that explains why the carbon factor moves; the network explorer for the regional DNO boundary that determines which regional factor a reader should be reading.

Generation tools: live mix, network explorer, dictionary

Three tools in one family sit at the live state of the system. The live generation dashboard reads the Elexon Balancing Mechanism Reporting Service on a five-minute heartbeat and shows the GB fuel mix, the demand, the interconnector flow with France, Belgium, the Netherlands, Ireland, Norway and Denmark, and the imbalance price. The dashboard is the first place to go for a "what is the grid doing right now" question and the only place on the workspace that holds a live numerical reading.

The network explorer illustrates the CIM structure with a synthetic, GB-shaped dataset and renders it as a navigable map; the data is illustrative, not a real network. It is modelled on the LTDS CIM Stage 2 publication of 29 May 2026, the first regulated network model in the Common Information Model format that every DNO has produced under the Ofgem derogation letter of 13 May 2026.¹ Dropping a pin on the map returns the nearest 132 kilovolt node, the DNO area, and an illustrative connection-status view at that location. The explorer is built for the first five minutes of a connection conversation: location, which operator owns the network here, and the visible headroom on the illustrative model.

The dictionary is the simplest of the three. It indexes 220 energy-sector terms with an in-browser search built on Fuse.js, and every entry cites a primary source with an as-of date. The dictionary is the most-used tool on the workspace because acronyms compound across the energy system. A reader who looks up SLC, GSP, BSP, BMU, MPAN, MPRN and Capacity Market in a single sitting will be reading from the four primary regulatory and operational source families (Ofgem licences, the Distribution Code, the Grid Code, the Capacity Market rules) at the same time.⁸

Hand off to: the engineering bench below for the per-tier statutory checks that turn a network-explorer reading into a connection design; the voltage page for the per-unit and transformer-ratio maths that the engineering bench computes against.

Engineering bench: power factor, voltage drop, cable sizing, transformer screening

The engineering bench runs the screening checks a planner or an electrical contractor needs at the front of a project. It is embedded below as a React surface served from the workspace API; the public route stays in the catalogue so the bench shares the citation register, the template and the navigation of the rest of the workspace. The bench covers six screens.

Power factor correction

The power factor correction screen takes the active power in kilowatts, the existing power factor, and a target power factor (typically 0.95 to 0.98 lagging on a commercial site to keep inside the local DNO's reactive charging structure). It returns the reactive power in kilovolt-amperes reactive that has to be supplied by a capacitor bank to meet the target, and the corresponding capacitance in microfarads at 400 volts three phase.

The formula behind the screen: reactive power needed Q = P times (tan(arccos(PF_old)) minus tan(arccos(PF_new))). The capacitor bank sizing then follows from the standard reactive-power identity Q = V² times 2 times pi times f times C, with V the line-to-line voltage, f the supply frequency (50 hertz under the Grid Code OC1 frequency band), and C the bank capacitance per phase.² The screen flags the result against the G99 Issue 2 connection requirements at the point of common coupling.⁵

Voltage drop screen

The voltage drop screen takes the line current in amperes, the cable resistance and reactance per kilometre, the cable length, and the load power factor. It returns the voltage drop in volts per phase, the line-to-line drop and the drop as a percentage of nominal, and flags the result against the operational and connection envelopes under G99 Issue 2 and Distribution Code DPC4 (plus or minus 6 percent operational, plus or minus 10 percent connection at 33 kilovolts and 11 kilovolts; plus 10 percent and minus 6 percent at the LV service under ESQCR regulation 27).^{5 3}

The bench's voltage drop screen uses the standard approximation ΔV is approximately equal to I times (R times cos φ plus X times sin φ) per phase in volts. The full per-unit base, the transformer ratio and the worked voltage-drop example with the G99 envelope check are on the voltage page so the bench can stay focused on the result rather than the derivation.

Cable sizing to BS 7671

The cable sizing screen takes the design current in amperes, the installation method, the ambient temperature, the run length and the permitted voltage drop in percent. It returns the minimum conductor size that meets BS 7671 Section 524 (voltage drop) and Section 433 (overload protection), and prints the relevant BS 7671 appendix tables (Appendix 4 for current-carrying capacity, Appendix 5 for installation method codes). The screen does not size protective devices, earthing or fault-current ratings; those still need a competent design under BS 7671 Chapter 41 and Chapter 54.

Transformer loading screen

The transformer loading screen takes the transformer rating in kilovolt-amperes, the nameplate impedance in percent, the primary and secondary voltages, and the load profile (peak load, peak load duration, ambient temperature). It returns the loading factor at peak, the hot-spot temperature rise under IEC 60076-7 against the manufacturer's thermal curve, and the headroom in kilovolt-amperes against the rated capacity. The screen flags the result against G99 connection requirements and against the operator's standing operational rating where it differs from the nameplate.⁵

G5/5 harmonic check

The G5/5 harmonic check takes a load's published harmonic emission profile (per harmonic order, as a percentage of fundamental) and a connection voltage level, and returns the resulting voltage distortion at the point of common coupling against the planning levels in ENA G5/5 Section 4.⁶ The bench will flag any harmonic order above the second compatibility level so the reader knows whether the load needs filtering before it can connect.

P29 unbalance check

The P29 unbalance check takes the single-phase load currents on each of the three phases at the point of common coupling and computes the negative-sequence current ratio. It returns the voltage unbalance percentage at the connection point and flags the result against the 2 percent limit at 132 kilovolts and below set by ENA P29 Issue 1, with the 1.33 percent allocatable to a single customer kept visible as the planner's working budget.⁷

The embedded bench

The React surface below is the same engineering tools workbench that lives at /gb-support/embed/gb-energy/engineering-tools. Embedding it here keeps the screening checks inside the workspace template alongside the catalogue and the source register. The bench is for screening only: any result that affects design, protection, procurement or a connection obligation still needs operator standards, project data, competent engineering review, and the relevant primary source from BS 7671 or the Engineering Recommendations cited above.

Hand off to: the voltage page for the per-unit base, the transformer ratio and a worked voltage-drop example with the G99 envelope check; the connections page for the firm or flexible connection decision that a bench screening result feeds into.