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A BITESIZED GUIDE TO AFDDs AND FIRE PROTECTION

Bitesize III

Electrical fi res continue to be a recurring danger in the UK, with recent events shockingly highlighting the risks. Arc Fault Detection Devices (AFDDs) have an important role to play in protecting people and property against the risks of fi re.

AFDDs are expected to be included in the 18th Edition of the IET Wiring Regulations which will be published in July 2018.

INTRODUCTION

• INTRODUCTION

• DEFINING WHAT IS MEANT BY ‘DANGER’

• THE BASIC PRINCIPLES OF SAFETY - BS7671

• TOO MANY FIRES FROM ELECTRICAL EQUIPMENT

• AFDDS DELIVER EXTRA PROTECTION AGAINST THE RISK OF FIRES

• WHAT’S THE ROLE OF AN AFDD?

• WHAT IS AN ARC FAULT?

• AFDDS – INSTALLATION AND TESTING

• WHERE AFDDS ARE USED

CONTENTS.


From a wiring regulations point of view, the defi nition of danger includes risks to persons, livestock and property during use of electricity in electrical installations.

DEFINING WHAT IS MEANT BY ‘DANGER’

DESIGN CONSIDERATIONS

Dangers from arcing, from overheating, from insulation faults and failures of wiring systems are all specifi cally referred to in the wiring regulations. These are important design considerations for every specifi er and installer when selecting components and planning an installation. High standards of workmanship and proper materials are also essential.


For the protection and safety of users, designers and installers need to give full consideration to the risks of fi res, arcing and burning, as well as power failures and other types of faults that can introduce hazards.

THE BASIC PRINCIPLES OF SAFETY - BS7671

In essence, electrical installations must be designed and installed so that the risk of ignition from electrical equipment, arcs and high temperatures is minimised (Chapter 13 BS7671).


The numbers are disturbing. 7,727 accidental fi res were recorded in “electrical distribution” Apr16 - Mar17 in England alone.(source www.gov.uk/government/collections/fi re-statistics).

TOO MANY FIRES FROM ELECTRICAL EQUIPMENT

SOURCE OF IGNITION

Of these, 5,574 had wiring, cables and plugs recorded as the source of ignition. There were also 3,442 domestic appliance fi res, with a total of 9,603 fi res attributed to faulty appliances and leads.


AFDDs are purpose-designed to provide additional protection from fi res caused by arc faults in 230V AC circuits.

Where AFDDs are specifi ed, they shall be installed at the origin of each (single phase AC) circuit that is to be protected I.e. in the consumer unit or distribution board. All AFDDs must comply with the relevant product standard: BS EN 62606.

AFDDs DELIVER EXTRA PROTECTION AGAINST FIRES


AFDDs are electronic protection devices that analyse the waveform of an A.C. circuit to detect arc fault conditions. They are pre-programmed with data on ‘normal’ arcs (such as from manual or automatic switching and normal operation of electrical equipment e.g. a motor in a washing machine), which means that they can recognise potentially dangerous arc faults.

WHAT’S THE ROLE OF AN AFDD?

AFDDs detect arc faults by continuous monitoring of the circuit for a variety of conditions, including the duration of the arc, the irregularity and the waveform. When they detect a fault, they disconnect the circuit from the supply to prevent the arc faultfrom leading to a fi re.


Arc faults are faults that occur either within or between conductors, for example, when insulation is damaged or a connection becomes loose. These arcing conditions can cause overheating, leading to ignition of the cable insulation and surrounding materials.

WHAT IS AN ARC FAULT?

Series arc faults are typically found in loose connections or frayed/damaged conductors. They occur within the one conductor only (L or N), so there are no fault currents to earth or neutral.

Parallel arc faults are typically found with damaged or degraded insulation that allows current fl ow between conductors. The current fl ow in these conditions will always be less than that of the operating load current –

which is why MCBs, RCDs. and fuses are unable to detect these faults. The current fl ow and arcing temperatures can cause overheating and ignition of the cable insulation and surrounding materials.


AFDDs are DIN mounted devices with integral MCB and RCD functions. They are installed in the consumer unit or distribution board.

Helpfully, AFDDs self-test on initial power up. The status indicator will confi rm that the circuit is in a healthy condition. If there is a fault, it will immediately indicate the fault condition.

AFDDs – INSTALLATION AND TESTING

HOW TO TEST

AFDDs include an integral test button (just like RCBOs). It is recommended that the operation of the test button is checked at initial install, at periodic inspections and regularly by the user.


In many countries including Germany, Austria, USA and Canada, AFDDs are used on circuits up to 20A or 32A, typically (though not exclusively) on socket outlet circuits.

The next edition of the wiring regulations (18th Edition) is expected to provide detailed guidance on requirements for, and use of, AFDDs in electrical installations from January 2019.

Because of the additional fi re protection they provide, AFDDs should be used in premises that have sleeping accommodation, in buildings that process, store or are built from fl ammable materials, and wherever irreplaceable items and artefacts are held, like museums and galleries.

WHERE AFDDs ARE USED


ANY QUESTIONS? CONTACTWylex Technical Team

Tel: +44 (0) 1543 438320

Fax: +44 (0) 1543 438321

Email: [email protected]

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