Be sure arc faults are not your fault
Byline goes here
Switchgear related accidents do not happen
often but when they do, they are likely to be
severe or fatal.
So while human error cannot ever be excluded,
manufacturers should ensure they build the
highest level of safety precautions into their
It has always been common practice to include
arc fault containment in medium voltage (MV)
and high voltage (HV) switchgear. Current is
not different on the low voltage (LV) end and,
in fact, might even be higher there.
Therefore, global IEC standards and Australia
Standard 3439 recommend arc testing.
However, a safety standard designed to empower
users of LV switchgear to insist manufacturers
prove their equipment prevents injury from
internal arc faults has sat largely idle since
But arc faults are not idle and do happen.
They can never be totally predicted or
prevented, and are usually caused by factors
outside the control of the manufacturer. What
can be controlled, though, is the extent of
the damage and injury caused by an arc.
The IEC 1641 standard marks the first attempt
to measure the ability of LV switchgear to
contain the effects of an arc. It is a set of
guidelines that can be requested by customers
requiring an assurance the switchgear assembly
specified provides a basic level of safety.
As such, IEC 1641 could help substantially
reduce the likelihood of serious injury and
Unfortunately, with its requirement for
destructive testing, testing to IEC 1641 can
add as much as $150,000 to the price of a
switchgear assembly. This, combined with a
common belief that switchgear with Form 4
separation type tested to BS EN 60/439-1:1994
offers sufficient protection against arcing,
means demand for the test has so far been
To date there have been only 30 tests
performed at ASTA approved laboratories.
This has led many to question the purpose of
IEC 1641 and the value of conducting testing.
To answer this, it is first necessary to
explore the potential consequences of an arc
fault, and to discover how its cost can far
exceed that of a one-off test to IEC 1641.
What is arcing?
An arc fault normally begins as a short
circuit between two or more contact points,
and can quickly develop to pose a serious
threat to personnel safety.
With an internal core temperature of 20,000°C,
an arc lasting just 500 milliseconds can cause
tremendous damage not just to a switchgear
assembly, but also to any other object,
including a human being, within its proximity.
Arc fault testing is a contentious issue; not
least because internal arc faults are most
often as a result of human error or
negligence. And there has been reluctance to
accept that arcing tests could be devised that
would be reproducible and meaningfully
representative of what might occur in
The behaviour of an arc and its secondary
effects may be impossible to predict.
Consequently, it has not been possible to
arrive at an internationally acceptable
standard for tests that would take into
account all the possible ramifications of
internal arcing faults.
The absence of such a standard means the
ability of a manufacturer’s assembly to
withstand the effects of an internal arc fault
may never be known until one actually occurs.
With damage caused by an arc potentially
amounting to thousands of dollars, not to
mention the cost of lost productivity,
switchgear customers should demand some extra
form of testing.
It is perhaps easier to say what IEC 1641 is
not. It is not a type test or a compulsory
test. Nor is it an attempt at a catch-all
definition of how arcing occurs and how to
Furthermore, the results of the tests are not
for presentation in the form of a test
certificate, since judgement as to the
effectiveness of the protection achieved is
solely a matter for agreement between the
manufacturer and the customer, and depends
greatly on the application in question.
Although many LV switchgear manufacturers were
carrying out their own safety testing as long
ago as 1984, there were no guides as to the
conditions under which this testing had to be
conducted. Consequently, a customer had no way
of comparing the safety of one manufacturer’s
switchgear with another’s.
The introduction of IEC 1641 has given
manufacturers common guidelines for carrying
out certain tests. Derived from a German
standard, VDE 0660 part 508, IEC 1641 provides
a number of criteria aimed at assessing the
performance of a LV assembly in the event of
an internal arc fault.
According to IEC 1641, an arcing test must be
performed at a voltage at least equal to the
highest rated voltage of the assembly. The
points within the assembly at which the arcs
are initiated then have to be chosen so that
the effects of the resulting arcs produce the
highest stresses. Usually, these points could
be on the incoming and outgoing sides of a
short-circuit protective device and across the
To pass the test, the switchgear, which must
have been tested with all doors and flaps
closed, must satisfy any of five criteria
selected by the customer (see box).
This criteria states structural integrity must
have been maintained, with all doors, flaps
and windows remaining closed and attached and
that the likelihood of injury to a person
working in the proximity of the board caused
by flames or hot gases is minimised.
Critics of the test question its value as a
true measure of safety in the event of an
internal arc fault, citing the failure of arc
fault tests such as those in the Australian
standard AS 1136 Appendix EE to consistently
achieve the same results. They argue that
little value should be attached to any arc
safety test, since the mysterious behaviour of
an arc makes exact repetition or reproduction
of an arc impossible.
But IEC 1641 is not concerned with the level
of internal damage to an assembly or to what
extent the spread of damage to other
compartments within that assembly may be
prevented. Instead, it is a set of guidelines
aimed at assessing the ability of an assembly
to limit the risk of injury to people in the
event of an internal arcing fault.
Test or not to test
There are several reasons why customers should
choose safety over cost when deciding whether
to opt for an assembly tested to IEC 1641.
Firstly, there is the fact that even
switchgear manufactured to BS EN 60/439-1:1994
will not provide total protection against
arcing. Of the manufacturers that have so far
carried out testing at ASTA approved
laboratories, all of which tested equipment
meeting the standard, 25% failed to pass one
or more of the tests set out by IEC 1641.
Secondly, and perhaps most importantly,
selecting those manufacturers capable of
meeting IEC 1641 will provide an important
assurance of quality that not all
manufacturers can meet.
By undertaking a continuous test program,
including tests such as IEC 1641 conscientious
manufacturers are showing a commitment to not
only the life of their products, but their
Negligence by ignorance is no longer an
acceptable defence in the eyes of the law,
therefore, every specifier and potential
customer of LV equipment assemblies should be
striving to use the best available. And in
doing so they should always put their
suppliers to the test.
Regina Roos is ABB sales manager LV Systems
Australia and NZ.
23 July 2003