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What is an AFDD and how does it work?

What is an AFDD and how does it work?

Amendment 2 to the IET 18th Wiring Regulations was published on 28th March 2022 and there are a number of key changes and additions. We’ll take a look at some of the key points which will be implemented on the 27th of September 2022 in this article.

Arc Fault Detection Devices

AFDDs have been a hot topic since the release of the 18th Edition in 2018. Since then we’ve been asked countless times the question; do you have to install Arc Fault Detection Devices? Until now the answer has been that AFDDs are only recommended.

This has now been clarified with the release of Amendment 2 BS 7671:2018+A2:2022 Regulation 421.1.7.  

The use of Arc Fault Detection Devices is now mandatory for single-phase AC final circuits supplying socket outlets (with a rated current no higher than 32A) in certain types of buildings i.e.

  • In Higher Risk Residential Buildings (HRRB)
  • In Houses in Multiple Occupation (HMO)
  • In Purpose Built Student Accommodation
  • In Care Homes

In all other instances, AFDDs are recommended for single-phase AC final circuits supplying 32A socket outlets.

Click here to view our range of AFDDs

What is an Arc Fault?

An Arc fault is where an electrical current jumps between two conductive materials.

The two main types of Arc Fault; are Parallel Arc Fault and Series Arc Fault. The most common causes of arcs include worn contacts in electrical equipment, breaks in cables and lose connections.

Why do Arc Faults Occur?

There are a number of reasons that could bring rise to an Arc fault. This list is not definitive however it covers the most common causes. 

  • Kinks or breaks in a cable
  • Cable wear due to frequent use
  • Damaged cables as a result of drilling during construction or DIY projects
  • Incorrectly stripped wires
  • Incorrect bonding
  • Lose connections in plug top
  • Defective plugs
  • Rodent bites

How do AFDDs work?

Arc Fault Detection Devices work using microprocessor technology to analyse the waveform of the electricity. They detect any unusual signatures which would signify an arc on the circuit. The AFDD will instantly terminate the power to the affected circuit effectively preventing a fire. They are considerably more sensitive to arcs than conventional circuit protection devices such as MCBs & RBCOs.

What is the purpose of Arc Fault Protection?

AFDDs have been designed to mitigate the risk of igniting an electrical fire in cables and equipment thus providing an additional level of protection.

Electrical fires can occur for a number of reasons;

  • Short-circuit and Overloads
  • Earth Leakage Currents
  • Overvoltage
  • Dangerous Electric Arcs

What are the types of electric Arc?

Series arc fault current

Series arc fault current – These occur due to damaged (crushed/broken) cables and loose connections.

Parallel arc fault current (Live-Neutral)

Parallel arc fault current occurs when there is a fault between the live and neutral (L-N). 

Parallel arc fault current (Live-Earth)

Parallel arc faults occur when the is a fault between the live and earth (L-E)

Let’s take a look inside an AFDD

What Does AFDD stand for?

AFDD is an acronym for Arc Fault Detection Device. A device is installed in a consumer unit to protect against Dangerous Arc Faults and provide protection against the risk of an electrical fire. 

What does HRRB stand for?

HRRB is an acronym for Higher Risk Residential Buildings. HRRBs are defined as buildings that are either over 18 metres in height or over six floors.

What does HMO stand for?

HMO is an acronym for Houses in Multiple Occupation. An HMO is a property rented out by at least three people, not of the same household/family who shares facilities such as kitchens and bathrooms. This is also known as a ‘house share’.

Click here to view our range of AFDDs

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