We have got a device which we prepare for marketing but there was a problem during testing so it did not pass necessary laboratory test. Problem is voltage durability e.g. device has test inputs (it's purpose is acquiring data based on measuring of bio-potencial) which were tested on 4 kV in duration of 10 seconds. Device goes up in smoke so we search for adequate overvoltage protection to protect it's input circuits.
Voltage should not exceed 20-30 Volts, so I am interested for a schematic that possibly includes standard spark gaps or varistors (not any exotic or expensive components) so we can achieve protection on 4-5 kV in duration over 15 seconds.
If anybody has a solution please send some links or ideas.