EoW September 2007

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EuroWire – September 2007 54
english technology news
50/60hz spark testers
– frightening or
enlightening?
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, including: the test
voltage cannot be set to the desired level;
the spark tester occasionally has to be
switched off due to continuous alerts for
non-existent defects; and transformer
burnout.
In order to resolve such issues, 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.
International standards set a maximum
limit of 10mA for electrical sources with
which a user may come into contact.
SIFMDC produces a wide range of spark
testers, including: 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, which also
ensures the long life of the transformers
and prevents burnout.
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.
This does not necessarily mean that
high frequency spark testers have to be
used. Factors to be considered include:
minimum and maximum φ 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 HazardIEEE, Spectrum, February
1972
SIFMDC – Italy
Fax : +39 035 4559358
Email:
Website :
Cemanco LC has introduced a new
product line for ceramic coated pulleys,
sheaves, rollers and similar wear parts,
all claiming superior wear properties and
performance.
The replacement parts are manufactured
with the tightest tolerances, balanced
for high rotation speeds and coated with
high impact bonding through use of a
detonation gun.
The surface is then polished to minimize
friction using a proprietary process,
the result being a ceramic coating that
is extremely wear resistant, has a high
impact resistance (no chipped edges), good electrical insulation and will outlast
regular spray coatings.
The replacement parts can help manufacturers reduce downtime and increase
productivity for a superior price/performance ratio.
Pulleys and rollers are available as standard replacement parts for suppliers such
as Niehoff, SAMP or Henrich, including multi-wire machines, with customisations
available for individual applications.
The process is also applicable for other non-metallic or metallic coatings.
Cemanco LC – USA Fax: +1 954 970 3056
Email: Website:
New line gives better wear and performance
Tightest tolerances on refurbished parts ▲