17th 18th edition bs7671 how this affects you. 17th-18th edition... · a bitesize look at rcds and...

A BITESIZE LOOKat RCDs and parts of the 18th edition DPC.

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17TH EDITIONBS7671

18TH EDITIONBS7671

HOW THIS AFFECTS YOU.

WHY CHOOSE ANYTHING LESS?

CONTENTS.


• INTRODUCTION.

• 17TH EDITION CHAPTER 31. WHAT IT SAYS ABOUT DIVISION OF THE INSTALLATION.

• INTRODUCTION TO 18TH EDITION DRAFT FOR PUBLIC COMMENT.

• 18TH EDITION. ADDITIONAL PROTECTION; SOCKET OUTLETS.

• 18TH EDITION. ADDITIONAL PROTECTION; CIRCUITS WITH LUMINAIRES.

• 18TH EDITION. CIRCUIT PROTECTOR (PE) CURRENTS – NOT DUE TO A FAULT.

• 18TH EDITION. TYPES OF RCD.

• 18TH EDITION. SELECTIVITY BETWEEN RCDS.

• 18TH EDITION. RCDS DISCONNECTING ALL LIVE CONDUCTORS.

• 18TH EDITION. SPECIAL LOCATIONS 730.

This document looks at some of the proposals, within the draft 18th Edition, relating to RCDs.

17th Edition Requires:

• Provision of additional protection (30mA RCD)

• Maintain power continuity

• Avoid unwanted tripping of RCDs

• Make provision for safe inspection, testing and maintenance?

HOW THIS AFFECTS YOU.The trend over the past 20 years has been towards more use of RCDs i.e. on a higher number of circuits and a wider number of locations. This is likely to continue. This document looks at some of the proposals.

Will the requirements change when the 18th Edition is published?


INTRODUCTION.

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How do you achieve power continuity and avoid unwantedtripping of RCDs and makeprovision for safe inspection, testing and maintenance?

Regulation 314.1 (i)

Every installation shall be dividedinto circuits as necessary to:

Avoid danger and minimize inconvenience in the eventof a fault.

HOW THIS AFFECTS YOU.The required number of individual circuits should be provided so that all healthy circuits provide power continuity and that only the individual circuit with fault is powered off.


17TH EDITION CHAPTER 31.

WHAT IT SAYS ABOUT DIVISION OF THE INSTALLATION.

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How do you achieve additional protection, power continuity andavoid unwanted tripping ofRCDs, and make provision forsafe inspection, testing and maintenance?

Regulation 314.1 (iv)

Every installation shall be divided into circuits as necessary to:Reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents (not due to a fault).

HOW THIS AFFECTS YOU.Cumulative currents within the protective conductor can be such that they add up to more than 50% of the rated residual operating current. This will cause the RCD to trip. Dividing equipment with PE currents over a larger number of circuits will help to avoid this risk.




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Regulation 314.1 (iii)

Every installation shall be dividedinto circuits as necessary to:Take account of hazards that may arise from the failure of a single circuit e.g. lighting.

HOW THIS AFFECTS YOU.Lighting circuits should be individually protected by their own protective device and not share devices such as RCDs that serve groups of circuits. Grouping circuits on one 30mA RCD should be avoided.




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Footnote: disconnection of all live conductors (L&N) may also be required for purposes of isolation and mechanical maintenance.


Regulation 314.1 (ii)

Every installation shall be dividedinto circuits as necessary to:Facilitate safe inspection, testing and maintenance.

HOW THIS AFFECTS YOU.The required number of individual circuits should be provided so that only the individual circuit in test or maintenance is safely powered off.




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The 17th Edition is due to bereplaced by the 18th Edition.A draft for public comment was released in 2017, comments willbe considered prior to publishingthe final content.

The 18th Edition is due to be published in July 2018 and all installations designed after December 31st 2018 are to comply with BS7671:2018. However, earlier adoption of thenew regulations is not precluded.Regulation 314 (Division of Installation) is maintained.

HOW THIS AFFECTS YOU.The DPC of 18th Edition contained a large number of changes, and additions that considerably expanded the content of the regulations. It willbe necessary for designers and installers to undertake training on these changes and additions.


INTRODUCTION TO 18TH EDITION DRAFT FOR PUBLIC COMMENT.

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Chapter 41

Additional protection by means of a 30mA RCD is required for:

Socket outlets rated to 20A. Mobile equipment rated to 32Aand for use outdoors.

Chapter 41

Additional protection by means of a 30mA RCD is required for:

Socket outlets rated to 32A.

Mobile equipment rated to 32Aand for use outdoors.

HOW THIS AFFECTS YOU.This change brings extra sockets and circuits into scope for additional protection by 30mA devices, and requires designers and installers to make provision for additional devices within consumer units and distribution boards.

18TH EDITION.

ADDITIONAL PROTECTION; SOCKET OUTLETS.


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Chapter 41No specific mention of RCDs on luminaire circuits in domestic (household) premises.

Chapter 41Additional requirements forcircuits with luminaires indomestic household premises, requiring additional protectionby an RCD rated not morethan 30mA for circuitssupplying luminaires.

HOW THIS AFFECTS YOU.This new requirement probably brings into scope circuits that were not covered by regulations group 522.6.200 (buried cables etc) and extends scope of 30mA protection to include luminaire circuits. This may require A Class RCD devicesin some circumstances.

18TH EDITION.

ADDITIONAL PROTECTION; CIRCUITS WITH LUMINAIRES.


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18TH EDITION.

CIRCUITPROTECTOR (PE) CURRENTS –NOT DUE TOA FAULT.

Regulation 314Division of the installation (Chapter31) requires designers to reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor (PE) currents, not dueto a fault. But gives no values forPE currents.

Regulation 531Section 531 cross references with 314 and includes specific values for PE currents, and division of the installation still requires designers to reduce the possibility of unwanted tripping of RCDs due to excessive protectiveconductor currents.

HOW THIS AFFECTS YOU.Extending the good practice of dividing the installation into a larger number of sub circuits as required to fully meet all 6 criteria listed in 314 may cater for these new requirements that are explained further on the next page.


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Regulation 531No specific value given for the maximum permitted (PE) circuit protector currents/earth leakage currents that are present duringnormal operating conditions.

Regulation 531The accumulation of circuit protector currents/earth leakage currents that are present during normal operating conditions shall not be more than 30% of the rated residual operating current of the RCD e.g. a PE of no more than 30% of 30mA.

HOW THIS AFFECTS YOU.Division of the installation into circuits with individual RCD/RCBOs may be an adopted method. Unless designers and installers are familiar with values for leakage currents (of equipment) under normal operating conditions and know that unwanted tripping will not occur.


18TH EDITION.

CIRCUITPROTECTOR (PE) CURRENTS –NOT DUE TOA FAULT.

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Regulation 531No detailed explanation of the types of RCD available or how the presence of DC components can be taken into account.

Regulation 531Different types of RCD are described e.g. type AC, type Aetc. Certain criteria are also provided on device behaviour when in the presence of DC components. Designers are required to select the appropriate RCD.

HOW THIS AFFECTS YOU.This section is expanded considerably but the additional information on types of RCD and the references to behaviours and operating characteristics should make RCD selection easier.


18TH EDITION.

TYPES OF RCD.

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18TH EDITION.

SELECTIVITY BETWEEN RCDS.

Regulation 536Where selectivity is necessary to prevent danger and required for proper functioning of the installation, manufacturers’ instructions shall be taken into account and the device characteristics shall be such that intended discrimination is achieved.

Regulation 536Where selectivity is required verificationshall be made either:

• By desk study

• By software tools

• By tests to the applicable product standard

• By manufacturer’s declaration

HOW THIS AFFECTS YOU.This section is expanded considerably but the additional information on types of RCD and the references to behaviours and operating characteristics should make RCD selection easier.


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HOW THIS AFFECTS YOU.These do not appear to be addressing the same point. The Draft of the18th Edition appearsto require RCDs to switch theneutral conductor as well as the live phase. Some RCD products do not switch all live poles. Designers needto be aware of which do.

18TH EDITION.

RCDS DISCONNECTING ALL LIVE CONDUCTORS.

Footnote - disconnection of all live conductors may also be required for other purposes isolation or mechanical maintenance. See also notes for TN, TT systems & special locations.

Regulation 531In a TN system where, for certain equipment in a certain part of the installation, the requirement of 411.4.5 cannot be satisfied, that part may be protected by an RCD.

Regulation 531An RCD shall disconnect all live conductors of the circuit protected.

DefinitionsRCD includes such devices as RCCB, RCBO, CBR and MRCD.

Footnote: disconnection of all live conductors may also be required for other purposes, isolation or mechanical maintenance. See also notes for TN, TT systems and special locations.


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18TH EDITION.

SPECIAL LOCATIONS 730.

Regulation 730730 does not appear in the 17th Edition but a number of similar applications do e.g. Marinas.

Regulation 730Onshore Units of ElectricalShore Connections:

Socket outlets rated to 63A shall be individually protected by a 30mA RCD.

The RCD shall disconnect all live conductors, phases and neutral.

HOW THIS AFFECTS YOU.730 is a new section and its content appears to follow the structure for other similar special locations. It contains similar requirements e.g. for sockets etc and that should make it reasonably straightforward to follow. However,it still needs detailed scrutiny.


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Miniature RCBOs with switched neutral as standard.


Note

This document is not a complete summary of proposed changes/additions to the wiring regulations and until the final publication is produced the proposals may be amended by the consultation process. Readers should obtain their own copy BS7671:2018.

N.B.

The term RCD is mentioned over 300 times in the draft of the 18th Edition. WHY CHOOSE ANYTHING LESS?

17th 18th edition bs7671 how this affects you. 17th-18th edition... · a bitesize look at rcds and...

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