Hot Line  (aka Live Line) insulator washing is a procedure to clean dirty or  contaminated insulators using a high pressure, high flow water stream.  Insulators are washed to prevent flashovers.  The water used must have  low conductivity.  The typical upper limit for conductivity is approximately 400 Micro-Siemens.  The water pressure is approximately 400 to 500 psi at the nozzle and typically under 200 psi at impact with the insulator. Normally only glass and porcelain insulators require live line washing. In polluted environments, it may be necessary to wash multiple times per calendar year.