On 6/21/2012 6:58 PM, ZR wrote:
> Differential mode filtering goes inside the outlet strip and ferrites on the
> outside take care of common mode on my filters.
When power people talk about common mode, they're talking about voltage
between neutral and the green wire. When RF people talk about common
mode, we're talking about a current that is common to all three
conductors and with no voltage between conductors. Commercial line
filters work on the voltage between neutral and green, but do nothing to
reduce what WE call common mode current unless the enclosure of the
filter is integral to, and bonded to, either the noisy device or the
device being protected the because the green wire bypasses the filter.
Most noise on the power line that causes us grief is what WE call common
mode, and the only good fix for that is a multi-turn ferrite choke wound
with all three conductors.
73, Jim K9YC
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