1. IEC-Publ. 52 (1960): Recommendations for voltage measurements by means of sphere-gaps (one sphere earthed).
2. Hueter, E.: Über die Messung des Scheitelwertes technischer Wechselspannungen mittels der Kugelfunkenstrecke. ETZ 57 (1936) 621–625.
3. Fiegel, H. E.; Keen, W. A.: Factor influencing the sparkover voltage of asymmetrically connected sphere gaps. Trans. AIEE, Commun. Electron. 76 (1957) 307–316.
4. Kuffel, E.: Influence of humidity on the breakdown voltage of sphere-gaps and uniform field gaps. Proc. IEE, Monograph No. 3 322 M, 108C (1961) 295.
5. Standring, W. G.; Browning, D. H.; Hughes, R. C.; Roberts, W. J.: Effect of humidity on flashover of air gaps and insulators under alternating (50 Hz) and impulse (1/50 μs) voltages. Proc. IEE 110 (1963) 1077–1081.