The vacuum state of vacuum switching elements after production is checked normally by Penning- or Magnetron methods (combined electrical and magnetic field). Vacuum in the range of 10-1 - 10-4 Pa can be measured in this way. After assembly into circuit breakers however, these methods are not applicable. HF interruption performance during making operation has been proposed earlier as a possible alternative. Further investigations show that differences in the number of HF prestrike current loops can be found in the pressure range of 10-1 - 105 Pa. Current chopping of DC arcs between 5 and 30 A during opening operation, may be another option for determination of the pressure range by measuring the lifetime of the arc, but the resolution in the vacuum range below 10-1 Pa is too poor.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.