Contamination deposits on arrester housings when wetted can cause external flashovers and, by disturbing the voltage distribution on the internal gaps, can lower the power frequency sparkover of the arresters. It has been found that the conditions that produce the lowest external flashover often do not cause the greatest reduction in sparkover. Separate tests are needed to adequately test the flashover of external insulation and the internal sparkover of an arrester. A proposed test is being developed for checking the sparkover characteristic of a wet, contaminated arrester.