G99
Engineering Recommendation G99
The rules for connecting generation or storage to a public distribution network when it doesn't fit . That means it runs in parallel with the network and is larger than G98 allows or isn't fully type tested. In Great Britain, you normally apply to the network operator before connecting, though some fast-track categories work differently. Northern Ireland uses NIE Networks' own version, G99/NI.
Using G99 in context
Reviewed
A distinction worth remembering
The current teaser names the interfaces between sources, loads, controls and protection. The Low-Carbon Electrics part of the electrical course goes further on charge points, heat pumps and the supply, and the electrical foundations are what it builds on.
Questions to take further
- How can I revise G99 beyond the definition?
- Explain what G99 describes, compare it with a related term and use it in a topic question. State any assumptions and what evidence you would need before applying the idea to real work.
Sources
- HSE: electrical safety questions — Isolation, competence and precautions before electrical work.
- IET: current BS 7671 edition and updates — BS 7671:2018+A4:2026 and the main subject areas updated by Amendment 4.
- IET: automatic disconnection of supply for island mode prosumer installations — Prosumer installations, island mode, earthing, system referencing and limited fault current from inverters.
- legislation.gov.uk: Electric Vehicles (Smart Charge Points) Regulations 2021 — Which charge points are covered, smart functionality, default charging hours, safety and where the rules extend.
- NIE Networks: generation connections — Northern Ireland's G98/NI and G99/NI connection routes.
- Ofgem: Smart Export Guarantee — Who the Smart Export Guarantee covers in Great Britain and how rates are set.
- GOV.UK: domestic battery energy storage systems — A 2020 government-published review of the safety risks of home batteries.
- legislation.gov.uk: Building Regulations 2010, regulation 12 — In England, the electrical work in a home that has to be notified to building control (a new circuit, a replacement consumer unit, or work on existing circuits in a special location), and what counts as a special location.
- GOV.UK: domestic electrical safety guidance — England guidance on domestic electrical safety; other nations require their own checks.
Where G99 fits in the learning path
The Low-Carbon Electrics section covers these units:
- EV Charging
- Solar PV and Batteries in Depth
- Heat Pumps, Smart Loads and the Supply
See this section in the full curriculum
This section is on the Plus path. Lesson availability depends on content review and your learning path.
Read, practise, return
1. Read it in context
- Smart, safe and low-carbon homesInstallation
- Battery Energy Storage SystemsThe Regs and Practice Papers
2. Try recalling, then explore practice
Use the memory prompt below to connect the vocabulary.
- 18th Edition — quiz previewPlus · The Regs and Practice Papers
3. Return to the meaning
After reading or practising, explain the idea in your own words, then check what you remembered.
Recall a related term
Which term fits this definition? Say it to yourself, then reveal it. This is a memory prompt, with no score or saved result.
Electrical power is the rate at which electrical energy is transferred, measured in watts (W) or kilowatts (kW). A 1 kW load transfers energy twice as fast as a 500 W load. In a DC circuit, power equals voltage multiplied by current. For AC loads, real power also depends on power factor, so multiplying voltage and current alone does not always give watts.
Electrical power
Read the Electrical power entryCompare related terms
Open a meaning to compare its role with G99, or follow its full entry.
Electrical power
Electrical power is the rate at which electrical energy is transferred, measured in watts (W) or kilowatts (kW). A 1 kW load transfers energy twice as fast as a 500 W load. In a DC circuit, power equals voltage multiplied by current. For AC loads, real power also depends on power factor, so multiplying voltage and current alone does not always give watts.
Read the Electrical power entryG98 — Engineering Recommendation G98
The rules for connecting small, fully type-tested generation of up to 16 A per phase to the public network. It runs in parallel with the low-voltage network, and 16 A per phase works out at 3.68 kW per phase, counting all the plant at the premises. In Great Britain, for a single premises, the installer can usually commission first and then notify the network operator within 28 days. Northern Ireland uses NIE Networks' own version, G98/NI.
Read the G98 entryBattery energy storage system — BESS
A battery and its control equipment, installed to store electricity and release it later. Often fitted alongside solar PV, it adds an energy source that can stay live when the supply is off, and running it in parallel with the network brings in the network operator's connection rules. BS 7671's Chapter 57 covers stationary batteries, and in homes PAS 63100:2024 deals with fire safety, including places a system doesn't go.
Read the Battery energy storage system entryDistribution network operator — DNO
The company that owns and runs the local electricity network that a property's supply comes from. It isn't the supplier who sends the bill: it deals with power cuts, new connections and supply upgrades. In Great Britain, Ofgem licenses DNOs, each for its own area, and the cut-out and its fuse belong to the DNO. In Northern Ireland, NIE Networks owns and runs the network, regulated by the Utility Regulator.
Read the Distribution network operator entryA definition is a start. Using it in a real question is where it sticks.