||Filters should perform in both symmetric and asymmetric mode. That is, they should remove differential and common mode noise. Some manufacturers offer comparatively smaller filters, but only specify asymmetric performance. These fail to remove differential noise.
||Filters should be rated for the appropriate maximum Line-to-Ground or Line-to-Line voltage for a 3 phase system. This eliminates the uncertainty of whether a filter will work at circuit voltages lower than the maximum filter rating.
||Filters should be rated for the appropriate circuit current and be able to withstand an overload of 140% for at least 15 minutes. This ensures the survival of the filter under overload conditions.
||Filters should be rated for low temperature rise in order to increase their durability and reliability
||Power filters should be listed by a Nationally Recognized Testing Laboratory (e.g. UL, Intertek). This ensures that a 3rd party has approved the safety of the filters.
||When testing for avionics at 400Hz power, filters should also use Power Factor Correction Coils. This ensures that high reactive currents at 400Hz are neutralized.
||Larger power filters (above 200 Amps) should have an option to be floor standing. This ensures that most of the weight is on the stand rather than on the shielded wall.
||Protection performance for HEMP/EMP filters should be according to MIL-STD-188-125 or IEC 61000-4-24. These are the preeminent standards used today for specifying conducted Point of Entry protection.
||When protecting a facility against HEMP/EMP, it is crucial to indicate if the filters will be installed inside or outside the protective shield. Only one side of the filter has the protective elements; the protection side must be that which is exposed to the threat.
||When using electronic power sources connected to filters, the source should have a transformer in its output circuitry. This minimizes unwanted interaction with filters.