Shaike, My thoughts on Immunity standards.
I feel that considering why the exemptions are given is useful. For DC powered units we are worried about pick up of disturbance on the DC cables or injection of disturbances from the AC supply. Radio Frequency disturbances are considered most likely to be due to pick up on cables - you have short cables (less than 3 metres) so pick up is unlikely - the test is not required. Fast Transient Burst disturbances are considered to be most likely to be generated on the AC supply (passing through the AC /DC supply) so the test is applicable. Voltage surge disturbances are considered to be most likely to be generated on the AC supply (passing through the AC /DC supply) so the test is applicable. If the DC cables were very long (greater than 10 metres) then there would be a possibility of pick up on the cables so the test would be applicable even if there were no connections to the mains via an AC/Dc supply. I hope this helps. Steve Austin austin@cassindustries .com
