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Should Emc Filters Have Separate Grounding?


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I would appreciate some help about whether EMC filters should have their own separate grounding. Generally I fit Schaffner input filters when we have EMC problems with our VFDs that drive borehole pumps, and have always taken the earth connection from the filter to a separate ground somewhere nearby, normally the copper pipework. Is this corrrect? The reason I ask is that we have a nu,ber of installations where the ADSL connection is being seriously effected when there is rain and stormy weather, and I´m wondering if this separate ground is actually making it worse...?

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The case of the EMC filter should be well bonded to the earthed frame of the VFD. This bonding needs to be high frequency bonding, not just a piece of cable as would be used for low frequency bonding. With high frequency bonding, it is surface area that counts, not cross sectional area. This does not meean fine stranded circular cable, rather flat braid or sheet metal. Ideally, the filter will be either bolted to the frame or heatsink of the VFD, or mounted on the same metalic gear tray as close as possible.

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