A BITESIZED GUIDE TO AFDDs AND FIRE PROTECTION

Transcription

1 A BITESIZED GUIDE TO AFDDs AND FIRE PROTECTION Bitesize III

2 INTRODUCTION CONTENTS. 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 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 WHERE AFDDS ARE USED

3 DEFINING WHAT IS MEANT BY DANGER 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. 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.

4 THE BASIC PRINCIPLES OF SAFETY - BS7671 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. 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).

5 TOO MANY FIRES FROM ELECTRICAL EQUIPMENT The numbers are disturbing. 7,727 accidental fi res were recorded in electrical distribution Apr16 - Mar17 in England alone. (source re-statistics). 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.

6 AFDDs DELIVER EXTRA PROTECTION AGAINST FIRES 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

7 WHAT S THE ROLE OF AN AFDD? 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. 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 fault from leading to a fi re.

8 WHAT IS AN ARC FAULT? 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. 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.

9 AFDDs INSTALLATION AND TESTING 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. 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.

10 WHERE AFDDs ARE USED 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 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.

11 ANY QUESTIONS? CONTACT Wylex Technical Team Tel: +44 (0) Fax: +44 (0)