WCA September 2007

Technology news

50/60hz 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. 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. 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 References [1]

SIFMDC – Italy Fax : +39 035 4559358 Email : info@sifmdc.com Website : www.sifmdc.com

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Wire & Cable ASIA – September/October 2007