Graham the 443 requirement to fit SPDs is based on the lightning chart and a "magic" formula. True it adds "transients due to switching" as an extra justification, but I am afraid I am far from convinced that they are necessary to protect electronic devices. Induced lightning current in an underground cable is very small, as the conductor spacing is tiny, so why is its length in the formula?
Of course the risk of issues with non-direct phenomena of atmospheric origin depends on the frequency of occurrence ???
Length is there for "common mode" as Mike points out.
Graham the 443 requirement to fit SPDs is based on the lightning chart and a "magic" formula. True it adds "transients due to switching" as an extra justification, but I am afraid I am far from convinced that they are necessary to protect electronic devices. Induced lightning current in an underground cable is very small, as the conductor spacing is tiny, so why is its length in the formula?
Of course the risk of issues with non-direct phenomena of atmospheric origin depends on the frequency of occurrence ???
Length is there for "common mode" as Mike points out.
