After more than 12 years in use, the National Rules for Electrical Installations ET101:2008 have been replaced with the new NSAI publication IS 10101:2020, writes Brendan Dervan.

The diagram below shows the evolution of the Wiring Rules in Ireland from the mid-1960s to the present day.

Figure 1: Evolution  of the Wiring Rules in Ireland (Sample illustration from Guidebook)

ET 101:2008 was the fourth edition of the Wiring Rules to be published. The first edition of the 'Wiring Rules' as we now know them was published in 1976 by the ETCI.

However the  unofficial 'Wiring Rules' in Ireland for many years were 'The Regulations for the Electrical Equipment of Buildings' as published by the Institution of Electrical Engineers (IEE) in the UK.

This book was simply referred to on both sides of the water as 'The Regs'. In fact when I started my apprenticeship in 1978 the 14th Edition of the Regs,  was part of the curriculum for the electrical apprenticeship courses in Ireland well into the 1990s due to the prevalence of City and Guilds courses here. 

It is unclear whether the new standard will be called the '5th Edition of the Wiring Rules' or the '1st Edition of IS10101'. Is worth noting that the UK maintained the edition number when the '16th EditionIEE Regs became British Standard BS7671. This is now in its 18th Edition

Changes in the new Standard

There are many important changes to the new standard as summarised below. Some of these relate to new or revised protective measures.

For example, the use of RCDs for lighting circuits in domestic premises, the requirements for arc fault detection devices (AFDDs) and surge protection devices (SPDs). Other changes are driven by climate action policy and associated emerging technologies such as charging points for electric vehicles and PV systems.

Another big change is that purchasers of the new standard are now given access to an on-line version which allows searching of the document using keywords.

The old volt drop tables have been removed. Instead a formula is provided for calculating the voltage drop. In my opinion this should be reviewed. At the very least worked examples should be provided in the future. 

Summary of changes since 4th Edition

  • Clause 411.3.4  - (RCDs) are now required to be installed on lighting circuits in domestic premises.
  • Clause 421.7  - Arc Fault Detection Devices (AFDDs) are now recommended for circuits installed in locations with particular risk
  • Clause 512.1.5 - Compliance with the Electromagnetic Compatibility (EMC) Directive 2014/30/EU
  • Clause 527 - Cables must now be rated to Class Dca s2, d2, a2 in accordance with EN50575.
  • Clause 531.3.3 Type AC RCDs are no longer recommended in new installations.
  • 534 - Selection of Surge Protection Devices (SPDs) – significant changes
  • Chapter 6 - Model certificates have now been removed.
  • Part 722 Supplies for Electric Vehicles – New Section
  • Part 710 Installations in Medical Locations – Multiple changes
  • Part 730 Onshore Units for Inland Navigation Vessels – New Section
  • Chapter 8: Energy Efficiency – New Section

The new standard has significantly more content than the previous editions of the Wiring Rules. It now contains a total of 764 pages compared 352 pages of the 4th Edition and to a mere 76 pages in the 1st Edition

Outline of the Standard

The new Standard comprises eight Chapters, 0 to 7 as listed below and a new standalone Part 8 which deals with energy efficiency. 74% of the standard is taken up by Chapters 4,5 & 7. 

Figure 2: Percentage of each Chapter of IS 10101 (Sample illustration from Guidebook)

The following is a brief summary of what is contained in each chapter along with references to the most significant changes:

Chapter 0 provides a brief outline of the standard and a list of normative references used throughout. The bibliography also includes 182 references to various international standards.

Chapter 1 is a relatively short chapter. It outlines the scope and fundamental principles. Much of what is discussed in this chapter is covered in greater detail in the subsequent chapters.

Chapter 2 provides definitions of the various terms used throughout the standard. The definitions in previous editions were spread throughout the standard.

Chapter 3 covers the general characteristics to be assessed when designing or modifying an electrical installation e.g. maximum demand and diversity, conductor arrangement and system earthing, external influences, compatibility, maintainability, continuity of service etc.

Chapter 4 concerns the various protective measures to be adopted to protect people and livestock and property against the hazards associated with electrical installations including electric shock thermal effects, over current and voltage disturbances.

Almost a quarter of chapter 4 is in the form of annexes. A total of 44% of the chapter deals with protection against overvoltage due to transients of atmospheric origin or due to switching.

The remaining third of the chapter deals with protection against electric shock, thermal effects and overcurrent followed by requirements for isolation. These sections are largely unchanged from the previous editions with the exception of the new requirement for arc fault detection devices (AFDDs)  and RCDs for domestic lighting circuits.

Figure 3: Typical Reduced Low Voltage / 110V 1 phase (Sample illustration from Guidebook)

Chapter 5 covers selection and erection of electrical equipment. It has  six main parts which by and large relate back to the protective measures discussed in Chapter 4.

These include: common rules; wiring system; switchgear and controlgear; earthing arrangements and protective conductors; other equipment and safety services.  

Each of these parts in turn comprises  between four and six sections. Almost 50% of Chapter 5 is in the form annexes for current capacity tables and the like.

Figure 4: Typical Connections  of SPDs and OCPDs (Sample illustration from Guidebook)

Chapter 6 deals with verification and certification which includes inspection, testing and certification of the electrical installation.

Chapter 7 deals with 'Special Installations or Locations' ( 20 No) which  involve increased risks and/or harsher conditions compared with those covered in Chapters 3-6.

The annexes in general give supplementary information and explanatory notes for specific items referred to in the rules. The most common annexe consulted is more than likely the current carrying capacities for cables.

Annexes maybe 'normative' which means in general must be complied with i.e. they form part of the standard or 'informative' which as the name suggests are given as general information only.

A number of  items are listed in the new standard as “under consideration”. It is excepted that there will be ongoing amendments and corrigenda issued by NSAI as the standard is adopted in the industry.

It should be noted that the Wiring Rules are not intended to take the place of a particular specification or to instruct untrained persons on how to design or install electrical services.

Key dates

The CRU is allowing a transition period of 28 months starting from April 1, 2020, for compliance with the new standard. The following is a summary of the key dates.

  • The transition period started on April 1, 2020. Electrical installations may be designed to the new standard from this date.
  • From February 1, 2021, all new electrical installations must be designed and certified to the new standard.
  • From August 1, 2022, all electrical installations must be certified to the new standard.
  •  Installations may be designed to the old standard until January 31, 2021, provided they are certified to at least a pre-connection stage by July 31, 2022.

Training courses

I am delighted to announce that I will be running the following on-line one-day training courses on the new Wiring Rules via Engineers Ireland from late September 2020.

  • WR1 - Understanding the New Wiring Rules
  • WR2  New Wiring Rules – Deep Dive –  Chapter Five
  • WR3 - New Wiring Rules –  Chapter 7 Explored

The aims and learning objectives of these three courses are given on my website –


Over the years many engineers including myself relied on the various guidebooks to the IEE 'Wiring Regs' which subsequently became BS7671 – now in its eighteenth edition.

While the ETCI did publish a guidebook to their own Wiring Rules it was no way as comprehensive as some of the illustrated guidebooks produced in the UK for example those produced by the Association of Supervisory and Executive Engineers (ASEE). This association later became the IIExE and  is now part of the IET (Institution of Engineering Technology).

I am currently working on a guidebook entitled 'The Wiring Rules in Ireland – An Illustrated Guide to IS 10101'. This is intended as a guidance document for the three one-day courses WR1, WR2 and WR3 referred to above.

Simplified diagrams

This guidebook  is being produced for the purpose of providing guidance to the new Wiring Rules. The guidebook uses simplified diagrams and tables to explain the requirements of the new standard. Some of these diagrams are included above

The guidebook mainly focuses on design aspects of electrical installations and is therefore aimed at engineers involved in the design of electrical services for large or complex buildings or others responsible for design of more standardised installations such as domestic, commercial or industrial installations.

The first thing to note is that it is not intended as a substitute for the standard but rather a companion guidebook.

The primary focus is on normal buildings, such as residential, commercial, industrial, educational, health care, hospitality including the twenty special locations covered in Chapter 7. Specialist building types such as data centres, pharmaceutical plants and other specialist manufacturing processes are outside the scope.

While it covers all earthing arrangements i.e. TN, TT, IT systems the main focus is on the TN-CS system which is the most common earthing arrangement in Ireland. Likewise the focus is predominantly on a.c. installations as opposed to d.c.

Demystify the rules

The guidebook follows the standard on a chapter by chapter basis and discusses the main points raised. It simplifies the narrative in the standard and aims to demystify the rules in using simplified diagrams, images, tables and worked examples

Most users of the Wiring Rules would agree that it is a difficult book to navigate at times due to the level of cross referencing between the different sections.

To assist in this aspect, the chapter, part, section and clause reference number are generally used throughout the guidebook so that they can be easily cross referenced with the actual standard

The guidance on Chapter 6 dealing with 'Verification and Certification' is covered in detail but it is not intended as a hands on training course for electricians involved in testing.

Some of the language in the standard is cumbersome at times. The guidebook aims to paraphrase the rules into simpler electro-technical language used by engineers and electricians.

Take for example the following rule ( 701.415.1): “In rooms containing a bath or shower, one or more residual current protective devices (RCDs) with a rated residual current not exceeding 30 mA shall provide protection of all circuits”. That type of clause will simply be replaced by: “In rooms containing a bath or shower all circuits shall be provided with 30 mA RCD protection”.

Guidebook comprises 56 individual 'units' 

  • Units 1-3: Provides an overview of the standard including Chapters 0, 1,2 & 3
  • Units 4-10: Covers Chapter 4 Protection for Safety
  • Units 11-31: Covers Chapter 5 Selection and Erection of Electrical Equipment
  • Units 32-34: Covers Chapter 6 Verification and Certification
  • Units 35-55: Covers Chapter 7 Special Installations or Locations
  • Unit 56: Covers Part 8 Energy Efficiency

The guidebook has taken a no-stone-unturned approach to the Wiring Rules. In other words any subject matter covered in the IS 10101 is referred to in the guidebook.

However certain practices that are not widely used in Ireland for example IT power supply arrangements, non-conducting locations, earth free local bonding etc. are discussed but not given the same level of detail as the more common practices.

It contains more than 130 illustrations, mainly original, more than 100 tables, 70 images and various worked examples. Many of the original tables in the standard have been adopted and presented in a clearer or more succinct format

If you are interested in learning more about these courses or purchasing the guidebook please contact:

Author: Brendan Dervan is a Chartered Engineer with more than 40 years’ experience in building services. He is currently represents Engineers Ireland on the NSAI’s TC2 which oversees the development of Wiring Rules. He was the founder of Dervan Engineering Consultants (DEC) established in 1999. In 2016 his practice merged with Cundall, a global multidisciplinary engineering consultancy firm. He retired from mainstream consultancy in 2019 and set up Best Training which provides specialist CPD services to the M&E sector.