Surge damage as a result of long cables connected to low voltage data systems can be prevented
RICHARD MEININGER & ROBERT BLOUCH
This article proposes a solution to the problems encountered when long cables are used to connect low voltage data systems, and either data interference or lightning surge damage is encountered. Three separate interference regimes are addressed: the low frequency data interference caused by shield current coupling to the signal lines; the surge potentials, due to lightning, encountered when a remotely grounded conductor is isolated from a local ground; and the high frequency interference that can propagate along a shield and cause high frequency electromagnetic interference to electronics at the ends of the shielded cables. This article focuses on shielded multi-conductor cables where problems are most frequently encountered. However, these issues also apply to coaxial cables that are used for data transmission at spectral frequencies below 300 kHz. The proposed solution is to use a termination device that provides optimal termination at both low and high frequencies, while also providing a safe bleed path for the induced surge voltage.
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