Arc Fault Detection Devices

In­creas­ing Pro­tec­tion

Arc fault pro­tec­tion devices (AFDD) use mi­cro­pro­cessors to identify char­ac­ter­istic cur­rent flow and voltage curves that in­dic­ate an arc fault and auto­mat­ic­ally trip the af­fec­ted cir­cuit.

This sig­ni­fic­antly re­duces the risk of fire due to faulty con­duct­ors and con­nec­tions. The pro­tect­ive func­tion of the AFDD has already proven its worth in­ter­na­tion­ally, and has been used in Ger­many since Feb­ru­ary 2016.

The 18th edi­tion of BS 7671, when pub­lished in July, re­com­mends the use of these to provide ad­di­tional pro­tec­tion against fire.

Mon­it­or­ing via Mi­cro­pro­cessor

An AFDD is ac­tiv­ated by both series and par­al­lel arc faults. Un­like cir­cuit break­ers or RCDs, an AFDD does not have an elec­tromech­an­ical trig­ger, but util­ises elec­tronic tech­no­logy to ana­lyse the sig­na­ture (wave­form) of an arc. It re­li­ably dif­fer­en­ti­ates between an arc fault and the sig­na­ture (wave­form) in nor­mal switch­ing and con­trol events, pre­vent­ing false trip­ping.

Po­ten­tial Causes

• Kink / break in a cable
• Cable wear due to frequent use
• Cable damage resulting from drilling or construction work
• Incorrect wire stripping
• Incorrect bending radii
• Loose screwed connections
• Defective wall plugs
• Rodents biting cables

An AFDD will trip the cir­cuit when a po­ten­tially haz­ard­ous arc oc­curs, elim­in­at­ing the res­ult­ing fire haz­ard.

Ring Fi­nal Cir­cuits

Con­trary to com­mon be­lief, AF­D­D’s do of­fer pro­tec­tion against arc faults in ring fi­nal cir­cuits and to the equip­ment be­ing fed from this cir­cuit. A series arc fault in one leg however, is un­likely to be at a dan­ger­ous level so will not be de­tec­ted. This is due to cur­rent in this in­stance flow­ing around the other leg of the ring. A series arc fault will be de­tec­ted in equip­ment and in flex­ible cables con­nec­ted to the ring fi­nal cir­cuit. Par­al­lel arc faults are de­tec­ted and dis­con­nec­ted in all parts of the ring cir­cuit and on all con­nec­ted equip­ment.

FAQs:

What does AFDD stand for?

Arc Fault De­tec­tion Device.

Where do I need Arc Fault De­tec­tion?

AF­D­D's should be in­stalled in a loc­a­tion that is eas­ily ac­cess­ible. They pro­tect 120 volt, single-phase, 15- and 20-ampere branch cir­cuits sup­ply­ing elec­trical out­lets or devices that are in­stalled in kit­chens, liv­ing rooms, fam­ily rooms, re­cre­ation rooms etc.

How does an AFDD work?

AF­D­D's work by pro­tect­ing against arc faults when they in­stant­an­eously trip a cir­cuit when they de­tect elec­tric arcs. This pre­vents the pos­sib­il­ity of a fire oc­cur­ring.
 

What types of cir­cuits can AF­DDs be used on?

The reg­u­la­tions spe­cify that 230 volts ac fi­nal cir­cuits that in­clude ring cir­cuits, ra­di­als, spurs and more. 

Ef­fect­ive Areas Of Pro­tect­ive Devices De­pend­ing On Fault Po­s­i­tion & Type

Fur­ther In­form­a­tion

The Hager tech­nical team con­trib­ute to a num­ber of key in­dustry pub­lic­a­tions, for AFDD we have been in­volved in the pre­par­a­tion of the BEAMA Guide to Arc Fault De­tec­tion Devices (AF­DDs)