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The Energy Networks Association (ENA) represents the interests of all electricity network operators in the UK. The Document Catalogue System is an online catalogue of engineering and Safety Health and Environment (SHE) documents available from the ENA. The engineering documents that you can access from the site are:Engineering Recommendations (EREC)Engineering Reports (EREP)Technical Specifications (TS)ACE ReportsEngineering Technical ReportsEngineering Equipment Assessment Lists
The Safety Health and Environment (SHE) documents that you can access from the site are:SHE StandardsSHE Position PapersSHE Briefings
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WARNING! Some of the older (pre 2003) documents available on this site were originally published by the now defunct Electricity Association. Please note that the ENA cannot take responsibility for the condition and content of these older documents and you are advised to seek advice before acting upon information held in them.
Information Exchange between Distribution Network Operators
Connections in Constrained Areas: Technical Guidance on the Options for Managing Curtailment at the Boundary between Network Operators
Live Tank Circuit Breakers to use on 400 kV Transmission System
Guide to the Application of Engineering Recommendation P28 Issue 2
Functional Test Requirements – Transformer Differential Protection
Functional Test Requirements – Voltage Protection
Protection of telecommunication lines from power lines
Engineering Technical Report 132 Issue 3 2025 Improving resilience of overhead networks under storm conditions.
Application Guide for Wildlife Protection Schemes for HV Overhead Lines
Reporting of incidents to the Health and Safety Executive (HSE) in accordance with regulation 31 of the Electricity Safety, Quality and Continuity Regulations 2002 (ESQCR)
Functional Test Requirements – Busbar Protection Relays
Managing the Risks Associated with the Provision of Multiple Connections in Close Proximity
Standard Application Form - Connection of Power Generating Modules to DNO Distribution Networks in accordance with EREC G99
Wildlife Protection Product Specification for HV Overhead Lines
Safe Working on the Low Voltage Electrical Distribution System
Power Quality Information Required for Heat Pumps and their Assessment
Working in or Near Water (including Flood Water)
Voltage Measurements for Assessment of Compliance with Statutory Voltage Limits
Instructions for Reporting to the National Fault and Interruption Reporting Scheme
Guide to the practical aspects of quality management associated with assessment of power system plant & products
Guide to the assessment of power system products for use by the ENA Member Companies
Part 2D: Procedure for the conformity assessment of protection products
Requirements for the connection of Fully Type Tested Micro-generators (up to and including 16 A per phase) in parallel with public Low Voltage Distribution Networks on or after 27 April 2019
EREC G98 Application Forms
Distributed Generation Connection Guide: G98 & G99
Requirements for the connection of generation equipment in parallel with public distribution networks on or after 27 April 2019
EREC G99 Application Forms
Separation between Wind Turbines and Overhead Lines: Principles of Good Practice
Code of practice for overhead to underground optical cable connections
Code of practice for the installation of ADSS optical cable
Post Trip Manual Reclosing of High Voltage Electrical Distribution Circuits
Distribution Network Operator Response to Reports of Low or Grounded Overhead Lines
Testing approach for merging units for protection sampling of instrument transformers in accordance with BS EN IEC 61869-13
Telecommunication Providers and Distribution Network Operators joint use of poles
Design and use of temporary scaffold guards and conductor support systems
Distribution cables of rated voltage 0.6/1/ (1.2) kV with XLPE insulation, concentric waveform copper wire and solid aluminium conductors
Environmental test requirements for protection and control equipment and systems
Guidelines for the Provision of Low Voltage Connections to Multiple Occupancy Buildings
Switchgear for use on 66 kV to 132 kV distribution systems Part 5 Inductive voltage transformers, capacitor voltage transformers, combined unit transformers and current transformers for use on 72.5 kV to 145 kV distribution systems
Power installations exceeding 1 kV a.c. – Design of high-voltage open-terminal stations
Aerial bundled conductors insulated with cross-linked polyethylene for low voltage overhead distribution
Specification for single circuit overhead lines of compact covered construction on wood poles for use at high voltage up to and including 33 kV
XLPE covered-conductors for overhead lines (having rated voltages Uo/U greater than 0.6/1 kV up to and including 19/33 kV)
Single core cables for use in substations having extruded insulation and rated voltages of 6350/11 000 volts, and 19 000/33 000 volts
Environmental classification and corrosion protection of structures, plant and equipment
Fittings for covered conductors for overhead lines (having rated voltages U0/U greater than 0.6/1 kV up to and including 19/33 kV)
Portable earthing equipment for overhead lines and substations
Complexity of Distribution Circuits Operated at or above 22kV
Stay strands and stay fittings for overhead lines
Guide to the application of Engineering Recommendation G5/4 in the assessment of harmonic voltage distortion and connection of non-linear equipment to the electricity supply system in the U.K
Calculation of fault currents in three-phase AC power systems (Application Guide to Engineering Recommendation G74)
Issue 3 - Amendment 8
Recommendations for the Connection of Generating Plant to the Distribution Systems of Licensed Distribution Network Operators
Engineering Recommendation G99/NI Issue 1 – Amendment 1 7 December 2023 Requirements for the connection of generation equipment in parallel with public distribution networks in Northern Ireland on or after 27 April 2019
Guidance on the application of Engineering Recommendation P2, Security of Supply
Security of Supply
Requirements for the Application of Protective Multiple Earthing to Low Voltage Networks
Analysis package for assessing the security contribution from distributed generation and electricity storage systems – Users’ guide
Analysis Package For Assessing Generation Security Capability - Users' Guide
Harmonic voltage distortion and the connection of harmonic sources and/or resonant plant to transmission systems and distribution networks in the United Kingdom
AC traction supplies to British Rail
Issue 2 Amendment 3 Recommendations for the Connection of Type Tested Small-scale Embedded Generators (Up to 16A per Phase) in Parallel with Low-Voltage Distribution Systems
Issue 1 Amendment 4 Requirements for the connection of generation equipment in parallel with public distribution networks on or after 27 April 2019
Voltage fluctuations and the connection of disturbing equipment to transmission systems and distribution networks in the United Kingdom
Guidelines for the design, installation, testing and maintenance of main earthing systems in substations
A guide for assessing the rise of earth potential at electrical installations
Framework for new low voltage housing development installations - Part 1 Design and planning
Framework for new low voltage housing development installations - Part 2 Materials specification
Framework for new low voltage housing development installations - Part 3 Installation and records
Framework for new industrial and commercial underground connections - Part 4 Design and planning
Framework for new industrial and commercial underground connections - Part 5 Materials specification
Framework for new industrial and commercial underground connections - Part 6 Installation and records
Framework for contestable diversionary and reinforcement works not exceeding 33 kV - Part 7 Contestable diversionary and reinforcement works
Procedure to meet the requirements on IEC 60909 for the calculation of short-circuit currents in threephase AC power systems Effective from 1st July 2021
This EREC sets out an outline procedure for a computer-based method for calculating circuit breaker short-circuit making and breaking currents in three-phase AC power systems having a nominal voltage above 1 kV. These currents are used for assessing the adequacy of switchgear to perform the required duty. The recommended procedure is also applicable for the calculation of short-circuit currents for other purposes, such as the determination of protection relay settings or the calculation of mechanical forces arising from short-circuit currents. To ensure that the results accurately represent system behaviour, it is a prerequisite of the procedure that the initial conditions for the short-circuit current calculation are determined from a load flow to establish pre-fault voltage levels at each busbar or node within the network. The mathematical process by which this is accomplished is not specified, but the factors which must be taken into account in the calculation are detailed for the various network components. It is the User’s responsibility to define load flow conditions leading to worst case short-circuit currents (e.g. maximum load on generators). Otherwise, there is a risk of insufficient circuit breaker ratings. The procedure outlined in this document is intended for use in situations where calculations of improved accuracy are required. This may be the case if actual short-circuit levels are close to equipment ratings or if short-circuit studies are carried out for operational purposes. Where maximum short-circuit currents are within plant and equipment rating, of which are determined by specific asset management strategy, simplified procedures which do not require a load flow calculation to determine the initial conditions for the short-circuit current calculation may be used. Such simplified procedures should, however, take full account of the short-circuit current contribution from all rotating plant (i.e. both synchronous and asynchronous machines). It is recommended that IEC 60909-0 is applied in these cases. The methodologies outlined in this document require modern computers and software to be executed. They are not intended to be used as a basis for the hand calculation of short-circuit currents.
Issue 2 + A1 June 2021 Foreword: Clarification on the implementation period for G74 Issue 2. Clause 7.3.2, Doubly fed induction Machines: incorrect X/R ratio deleted. Issue 2 June 2020 Major revision of Issue 1 to align the document with the latest normative reference: IEC 60909-0:2016. This issue includes the following principal technical changes: Introduction: Clarification on the application of G74 has been added. NEW Clause 2.2: Terms and definitions. Clause 5: Clarifications added regarding the ‘initial symmetrical short-circuit current’, ‘aperiodic component of short-circuit current’, and the ‘peak short-circuit current’. Clause 6: NEW detailed guidance on methodologies for short-circuit current calculation including: • Clause 6.1: The concept of the superposition method; • Clause 6.2: Calculation of initial short-circuit current; • Clause 6.3: Peak short-circuit current; • Clause 6.4: Short-circuit breaking current, including peak short-circuit breaking current for all fault types. Clause 7 now covers modelling of system components – there have been major changes: © 2021 Energy Networks Association All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written consent of Energy Networks Association. Specific enquiries concerning this document should be addressed to: Operations Directorate Energy Networks Association 4 More London Riverside London SE1 2AU This document has been prepared for use by members of the Energy Networks Association to take account of the conditions which apply to them. Advice should be taken from an appropriately qualified engineer on the suitability of this document for any other purpose. ENA Engineering Recommendation G74 Issue 2 2020 + A1 2021 Page 4 Clauses 7.2-7.4 now covers plant (previously Clause 9, Rotating Plant, in Issue 1) with NEW guidance added as follows: • Clause 7.2.1 – 7.2.3: use of the three methods (single time constant, equivalence reactance, current superposition) for calculation of short-circuit current. • Clause 7.2.4: Updated guidance on considerations for the short-circuit contribution of loads. • Clause 7.3: NEW guidance on converter-driven plant (variable speed wind turbine generators and photovoltaic inverters). • Clause 7.4: NEW guidance on HVDC terminals and FACTS. Clause 7.5 now covers representation of system equivalents (previously Clause 6 in Issue 1) with some changes regarding reference to sequence reactance calculation formulae. Clause 7.6 now covers passive network components (previously Clause 7 in Issue 1) with some NEW guidance: • Clause 7.6.4: NEW guidance added for Series Capacitors, Series Reactors, Thyristor Controlled Series Compensation (TCSCs)
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