National foreword

This British Standard is the UK implementation of EN IEC 60909‑0:2026. It is identical to IEC 60909‑0:2026. It supersedes BS EN 60909‑0:2016, which will be withdrawn on 30 September 2029.

Contractual and legal considerations

This publication has been prepared in good faith, however no representation, warranty, assurance or undertaking (express or implied) is or will be made, and no responsibility or liability is or will be accepted by BSI in relation to the adequacy, accuracy, completeness or reasonableness of this publication. All and any such responsibility and liability is expressly disclaimed to the full extent permitted by the law.

This publication is provided as is, and is to be used at the recipient’s own risk.

The recipient is advised to consider seeking professional guidance with respect to its use of this publication.

This publication is not intended to constitute a contract. Users are responsible for its correct application.

Compliance with a British Standard cannot confer immunity from legal obligations.

This British Standard was published under the authority of the Standards Policy and Strategy Committee on 30 September 2026.

This European Standard was approved by CENELEC on 27 August 2026. CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czechia, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and United Kingdom.

European foreword

The text of document 73/220/CDV, future edition 3 of IEC 60909‑0, prepared by TC 73 "Short-circuit currents" was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as EN IEC 60909‑0:2026.

The following dates are fixed:

This document supersedes EN 60909‑0:2016 and all of its amendments and corrigenda (if any).

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.

Any feedback and questions on this document should be directed to the users’ national committee. A complete listing of these bodies can be found on the CENELEC website.

Endorsement notice

The text of the International Standard IEC 60909‑0:2026 was approved by CENELEC as a European Standard without any modification.

In the official version, for Bibliography, the following notes have to be added for the standard indicated:

FOREWORD

The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with may participate in this preparatory work. International, governmental and non-governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international consensus of opinion on the relevant subjects since each technical committee has representation from all interested IEC National Committees.
IEC Publications have the form of recommendations for international use and are accepted by IEC National Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any misinterpretation by any end user.
In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications transparently to the maximum extent possible in their national and regional publications. Any divergence between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.
IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any services carried out by independent certification bodies.
All users should ensure that they have the latest edition of this publication.
No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and members of its technical committees and IEC National Committees for any personal injury, property damage or other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC Publications.
Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is indispensable for the correct application of this publication.
IEC draws attention to the possibility that the implementation of this document may involve the use of (a) patent(s). [IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in respect thereof. As of the date of publication of this document, IEC had not received notice of (a) patent(s), which may be required to implement this document. However, implementers are cautioned that this may not represent the latest information, which may be obtained from the patent database available at https://patents.iec.ch and/or www.iso.org/patents. IEC shall not be held responsible for identifying any or all such patent rights.

IEC 60909-0 has been prepared by IEC technical committee 73: Short-circuit currents. It is an International Standard.

This third edition cancels and replaces the second edition published in 2016. This edition constitutes a technical revision.

This edition includes the following significant technical changes with respect to the previous edition:

restructuring and complementing of the clauses, especially restructuring and updating of Clause 6.
restructuring of subscripts.

The text of this International Standard is based on the following documents:

Full information on the voting for its approval can be found in the report on voting indicated in the above table.

The language used for the development of this International Standard is English.

This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are described in greater detail at www.iec.ch/publications.

A list of all parts in the IEC 60909 series, published under the general title Short-circuit currents in three-phase AC systems, can be found on the IEC website.

The committee has decided that the contents of this document will remain unchanged until the stability date indicated on the IEC website under webstore.iec.ch in the data related to the specific document. At this date, the document will be

reconfirmed,
withdrawn, or
revised.

INTRODUCTION

Main aim of IEC 60909‑0 is calculation of maximum and minimum short-circuit currents of bolted short circuits (see 5.2.4). Calculation results can serve as input for further evaluations such as calculation of arcing current as described in, for example, IEEE 1584.

1 Scope

This part of IEC 60909 is applicable to the calculation of short-circuit currents

in low-voltage three-phase AC systems,
in high-voltage three-phase AC systems, and
operating at a nominal frequency of 50 Hz or 60 Hz.

Systems at highest voltages of 550 kV and above with long transmission lines are outside the scope of this document.

This document establishes a general, practicable and concise procedure leading to results which are generally of acceptable accuracy. For this calculation method, an equivalent voltage source at the short-circuit location is introduced. This does not exclude the use of special methods, for example the superposition method, adjusted to particular circumstances, if they give at least the same precision. The superposition method gives the short-circuit current related to the one load flow presupposed. This method, therefore, does not necessarily lead to the maximum respective minimum short-circuit current.

This document deals with the calculation of short-circuit currents in the case of balanced or unbalanced short circuits.

A single line-to-earth fault occurring in networks with isolated or resonant earthing of the neutral point is beyond the scope of this document.

For currents during two separate simultaneous single-phase line-to-earth short circuits in an isolated neutral system or a resonance earthed neutral system, see IEC 60909‑3.

Short-circuit currents and short-circuit impedances can also be determined by system tests, by measurement on a network analyser, or numerical simulations with electromagnetic programs. In existing low-voltage systems, it is possible to determine the short-circuit impedance on the basis of measurements at the location of the prospective short circuit considered.

The calculation of the short-circuit impedance is in general based on the rated data of the electrical equipment and the topological arrangement of the system and has the advantage of being possible both for existing systems and for systems at the planning stage.

In general, two types of short-circuit currents, which differ in their magnitude, are considered:

maximum short-circuit current which determines the capacity or rating of electrical equipment;
minimum short-circuit current which can be a basis, for example, for the selection of fuses, for the setting of protective devices, and for checking the run-up of motors.

NOTE The current in a three-phase short circuit is assumed to be made simultaneously in all poles. Investigations of non-simultaneous short circuits, which can lead to higher aperiodic components of short-circuit currents, are beyond the scope of this document.

This document does not cover short-circuit currents deliberately created under controlled conditions (short-circuit testing stations).

This document does not deal with the calculation of short-circuit currents in installations on board ships and aeroplanes.

This document does not distinguish between grid-forming and grid-following converters for the calculation of short-circuit currents.

2 Normative references

3 Terms and definitions

4 Symbols, subscripts and superscripts

4.1 General

4.2 Symbols

4.3 Subscripts

4.4 Superscripts

5 Characteristics of short-circuit currents: calculating method

5.1 General

5.2 Method of calculation

6 Modelling of electrical equipment for short-circuit calculations

6.1 General

6.2 Overhead lines and cables

6.3 Transformers

6.4 Reactors

6.5 Capacitors

6.6 Non-rotating loads

6.7 Network feeders

6.8 Synchronous machines

6.9 Asynchronous machines

6.10 Power electronic converters

6.11 Power station units

6.12 Power plants

6.13 Converter-fed motors

6.14 FACTS devices and HVDC transmission systems

7 Calculation of initial short-circuit currents

7.1 Overview

7.2 Three-phase short circuit

7.3 Line-to-line short circuit

7.4 Line-to-line short circuit with earth connection

7.5 Line-to-earth short circuit

8 Calculation of peak short-circuit currents

8.1 Single-fed three-phase short circuit

8.2 Multiple-fed three-phase short circuits

8.3 Unbalanced short circuits

9 Calculation of symmetrical breaking currents

9.1 Single-fed three-phase short circuits

9.2 Multiple-fed three-phase short circuits

9.3 Single-fed and multiple-fed unbalanced short circuits

10 DC component and unbalanced asymmetrical breaking current

11 Calculation of steady-state short-circuit currents

11.1 General

11.2 Three-phase short circuits

11.3 Unbalanced single-fed and multiple-fed short circuits

12 Short circuits at the low-voltage side of transformers, if one line conductor is interrupted at the high-voltage side

13 Terminal short circuits of asynchronous motors

14 Thermal equivalent short-circuit current and Joule integral

Bibliography