Better late than never, I say. There is at last a groundswell of interest in arc fault device detectors prompted by the example of the US. It requires arc fault circuit interrupters (AFCIs) in dwelling units, while UL standard 1699-2009 governs devices themselves. Many other countries have called for the introduction of product standard defining devices that afford protection against dangerous electric arcs, now identified as a major cause of electrical fires.
Which international bodies are working on AFDD standards?
The International Electrical Commission (IEC) is one.
In 2008, Germany took the standard issue by the scruff of the neck: it proposed to the IEC Community that they get moving on standardizing electric arc protective equipment. Member countries unanimously approved the German proposal.
At the end of 2008, the IEC began work in technical sub-committee SC 23E.
The goal was to arrive at an international standard for an Arc Fault Detection Device (AFDD), whether standalone or combined with a conventional circuit-breaker or RCBO.
The IEC was able to draw on the UL’s work in UL standard 1699 for AFCIs. However, AFCIs are intended for 120V/60Hz grids, whereas IEC had to take into account 230V/50Hz single phase circuits. Additional experimental work was therefore necessary.
How difficult was it to model an electric arc?
In a word, very.
The IEC’s first step was to create a benchmark electrical arc with sufficiently clear-cut characteristics to define a dangerous electric arc.
But how do you define something that by its very nature is as crazy, random, and unpredictable as an arc? Still, the IEC members tried. I salute their work on devising a test method of triggering a regularly repeating arc that allowed such a protective device to be tested.
What definitions and specifications have been arrived at?
The IEC then got stuck into some serious research. IEC members operated in specialized research labs with a two-fold aim:
• Define dangerous and harmless arcs
• Establish at what energy output an electric arc on a 230V, 50Hz power line becomes dangerous.
The research eventually settled on a threshold beyond which the energy, or heat, generated by an arc should be considered dangerous. It was 100 joules. This energy is high enough to spread fire to surrounding materials.
How fast should AFDDs respond?
Fast, very fast.
As electrical arcs reach very high temperatures that run into thousands of degrees, they easily ignite power cables. A critical specification was therefore decided: that the greater the force of an arc, the faster the AFDD should trip. For very high arc currents, in particular, AFDDs should detect and trip in less than 120 milliseconds.
When will the new standard be issued?
IEC members countries have just given their approval to the final draft of international standard. IEC 62606 will soon be available on the IEC website. It will define what an arc fault detection device is and spell out the procedure for performing standardized AFDD tests.
The next step will be to which circuits in electrical installations AFDDs should protect. That will be the subject of international standard IEC 60364.
Any thoughts on further AFDD-related issues that standards bodies should address? Feel free to share them with us.