WCA September 2007

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Technologynews
Wire & Cable ASIA – September/October 2007 64
SIFMDC, Italy, used the wire Russia
trade fair in May to launch a new
micro-processor-based spark tester.
Questions were raised by visitors to the
company’s stand about the need to
resolve certain issues related to spark
testers and their use.
Customers were asked whether or not
they had connected the copper of
conductor to the ground. Some
responded that they did not always
connect it, and only did so on certain
occasions, which showed a slight
improvement but did not resolve the
problem entirely. It was also found that
most were using high frequency spark
testers, and that cables were tested at
line speeds no greater than 200m/min.
Customers were also asked why they
did not use a 50Hz spark tester, to
which they replied, ‘because it is
dangerous.’
SIFMDC’s Claudio Formenti points out
that misinformation is common. There
are official documents available on the
subject of electrical current threshold
tests, that prove that an individual who
comes into contact with an electrical
source is able to let go – the aptly
named ‘let-go’ currents[1]. The level for
women is around 10mA and for men
around 15mA.
SIFMDC produces a wide range of
spark testers, including the 50/60Hz,
small series with a 3mA limited current;
compact and large series with a 7mA
limited current; 250Hz, 500Hz and
3kHz, small series with a 3mA limited
current; and DC with a current limited
to less than 3mA.
These spark testers do not exceed the
required level of current. They are built
with a protective casing to prevent
accidental contact, and are fitted with
safety switches for cutting off the power
supply if the casing should open.
Additional safety is provided by the
intrinsic protection of the self-limiting
transformers.
High frequency spark testers are
designed to resolve issues with super
high velocity (2,500m/min) testing, in
accordance with standard UL1581,
which requires that the defect remains
inside the electrode for 9 sinusoids.
In theory, 50Hz spark testers could be
used with longer electrodes in order
to satisfy the standard. In practice,
however, manufacturers build devices
with higher frequencies.
Factors to be considered include:
minimum and maximum Ø of the cable,
test voltage and line speed ranges,
test standards (EN50356, UL1581,
GOST2990-78), and whether or not the
cable is capacitive.
Another advantage of working with low
frequency spark testers is that they can
be checked periodically with standard
probes calibrated at an SIT (Italian
Calibration Centre) or similar, therefore
gaining metrological integrity.
References
[1] Dalziel, Ogden, Abbot, Effect of Frequency
on Let-Go Currents, Transactions of AIEE,
Volume 62, December 1943, and Dalziel,
Electric Shock Hazard IEEE, Spectrum,
February 1972
SIFMDC – Italy
Fax: +39 035 4559358
Email:
Website:
50/60hz testers – frightening or enlightening?
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