Distribution Code (DCode)

Page type: primary-anchored (mirrors DCode, ENA)

Last updated: 6 April 2026

The DCode is the GB industry code governing the technical and operational aspects of electricity distribution networks. It covers the technical parameters, operational procedures, and planning standards for connection to and use of DNO distribution systems. Administered by ENA via the Distribution Code Review Panel (DCRP). Ofgem approves all modifications.

Source file: ~/knowledge/sources/energy-networks/dcode.md

What the DCode does, in plain language

The DCode is the technical rulebook for electricity distribution networks. It tells DNOs how to operate their networks safely, how to plan for future demand, and what technical standards generators and customers must meet when connecting. It covers everything from voltage limits and power quality to demand forecasting, safety coordination, and what happens when the lights go out.

Unlike the BSC or REC (which are about commercial arrangements), the DCode is an engineering code. It deals with fault levels, voltage regulation, protection settings, and the physical interface between the network and its users. Many of its requirements are detailed in ENA Engineering Recommendations (like G99 for generation connections or P2 for security of supply), which are referenced in Annex 1.

Structure

The DCode has six main sections plus two Annexes. Each section is identified by a prefix code.

DI. Distribution Introduction

Purpose, scope, legal framework (Distribution Licence SLC 21), relationships with other codes, modification process, applicability matrix.

DGD. Distribution Glossary and Definitions

All defined terms, interpretation rules, abbreviations.

DGC. Distribution General Conditions

General obligations: DNOs must plan, develop and operate per Code (DGC.2). Users must comply with applicable provisions (DGC.3). Data exchange, confidentiality, compliance monitoring.

DOC. Distribution Operating Code (10 sub-sections)

Operational requirements for running the distribution system:

• DOC1: Demand Control: emergency demand disconnection, voltage reduction, rota disconnection. Coordination with NESO via Grid Code OC6/OC7
• DOC2: Operational Liaison: communication between DNO and Users, outage coordination
• DOC3: Operating Margins: reserve on the distribution system
• DOC4: Safety Coordination: safety procedures for work on/near the network
• DOC5: Event Reporting: reporting significant events, classification, timescales
• DOC6: Demand Forecasting: Users provide forecasts to DNO
• DOC7: Distributed Generation: operational requirements for distribution-connected generators (active/reactive power, fault ride-through, loss of mains, anti-islanding, frequency response)
• DOC8: Embedded HVDC: requirements for HVDC in distribution
• DOC9: Voltage Control: voltage regulation within ESQCR 2002 limits, reactive power management
• DOC10: System Restoration: post-disruption restoration, coordination with NESO, Black Start from DG

DPC. Distribution Planning and Connection Code (7 sub-sections)

Planning standards and connection requirements:

• DPC1: Connection Applications: application process, information, DNO response timescales
• DPC2: Demand Connections: technical requirements, power quality (harmonics per G5, flicker per P28, unbalance per P29)
• DPC3: Generation Connections: technical requirements for DG. References ER G98 (Type A), G99 (Type B/C/D), G100 (export limitation)
• DPC4: HVDC Connections: HVDC-specific requirements
• DPC5: DSR and Flexibility: demand-side resources, flexibility services
• DPC6: Planning Standards: security of supply per ER P2, network design criteria
• DPC7: Data Registration: data exchange between Users and DNO

DDRC. Distribution Data Registration Code

Registration of connection data, data maintenance, data exchange with BSC and DCUSA.

Annex 1: Engineering Recommendations

ENA ERs implementing DCode requirements. Key ones: G5 (harmonics), G98 (small generation), G99 (larger generation), G100 (export limitation), P2 (security of supply), P28 (voltage fluctuations), P29 (voltage unbalance).

Annex 2: Other Industry Documents

Documents with material impact on Users, not formally part of the DCode.

Key cross-references

• Electricity Distribution Licence SLC 21: requires DNOs to maintain DCode
• Grid Code: DOC1 coordinates with OC6/OC7 (demand control); DOC7 with CC/ECC (DG); DOC10 with OC9 (restoration)
• ESQCR 2002: statutory voltage limits (DOC9)
• DCUSA: distribution use-of-system charging
• BSC: settlement metering
• ER G98, G99, G100: generation connection standards (DPC3)
• ER P2: security of supply standard (DPC6)
• Energy Act 2023 Part 6: future code governance reform

Defined terms

See full register in source file (~/knowledge/sources/energy-networks/dcode.md). Key terms: DNO, User, Distribution System, Distributed Generation, Fault Level, Engineering Recommendation, DCRP.

Current status

• Version: Issue 58 (effective 10 March 2025)
• Administrator: ENA (on behalf of all DNOs)
• Governance: Distribution Code Review Panel (DCRP)
• Recent changes: System Restoration Standard implementation, Grid Code alignment for DER
• Energy Code Reform: Energy Act 2023 Part 6 will bring DCode under new code manager

Technical notes

• The DCode applies to voltages from 132kV downwards in England and Wales. In Scotland, 132kV is transmission voltage (owned by SSEN Transmission/SP Transmission), so the Scottish DCode boundary is lower.
• IDNOs (Independent DNOs) are also bound by the DCode via their licence conditions.
• DOC7 (Distributed Generation) and DOC10 (System Restoration) are the most frequently modified sections, reflecting the growth of distributed generation and the introduction of the Electricity System Restoration Standard.

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