Telecommunication networks outside plant facilities are subjected to voltage and current surges caused by lightning storms or by transients on nearby power lines. The impulse voltage induced on a cable pair is common-mode in nature, that is, from each conductor to ground simultaneously. However, the common-mode voltage is converted to a differential-mode voltage between the two conductors of the cable pair by the unbalance of the conductors or the asymmetrical operation of surge protectors. Common-mode voltage levels have been measured in several surveys but not differential-mode voltages. This paper provides statistical models that derive expected differential-mode voltages from measured common-mode voltages. The differential-mode voltages are of interest since they may interfere with digital transmission, and may cause a large number of bit errors.
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