Spark gap

A spark gap for use in a power supply of medium voltage and low voltage networks, comprising a housing having an interior, two rotationally symmetric electrodes mounted in the interior of the housing, a hollow-cylindrical arc space being defined between the two electrodes for an arc forming in the event of a spark-over and a follow-on current thereof, the arc space having a longitudinal center axis, the two electrodes being arranged one behind the other in a direction of the longitudinal center axis and being arranged with a gap therebetween, a disk of an electrically insulating material extending perpendicularly of the longitudinal center axis being positioned in the gap between the electrodes for electrically separating the two electrodes from one another, the disk having an opening adapted to the hollow-cylindrical arc space for forming a spark-over place for the arc, the arc space comprising a rotationally symmetric arc chamber concentric to the longitudinal center axis for the follow-on current, the arc chamber being located between the two electrodes, wherein the arc chamber has an electrically active length, the electrically active length being differently selectable while maintaining external dimensions of the spark gap.