EMI filter

01

Read a three-phase EMI filter datasheet: a worked example

LinMot’s NF01-FN258-16-07 datasheet lists a maximum continuous voltage of 480 VAC at 50 °C and a current rating of 16 A at 50 °C, or 17.5 A at 40 °C. Its 7.5 kW typical-drive example is calculated at rated current, 440 VAC and cos φ = 0.8; the footnote also identifies drive, motor and application efficiency. It is not a general power-to-filter selection rule. [1]

The same sheet specifies a 2-second high-potential test of 2,650 VDC phase-to-earth and 2,100 VDC phase-to-phase. These are DC test voltages, not continuous operating voltages or AC withstand ratings. IP20, 20 W loss at 25 °C/50 Hz and a −25 to +100 °C operation/storage range are separate entries; the temperature range does not promise full rated current at 100 °C. [1]

Its overload entries are four times rated current at switch-on, without a stated duration there, and 1.5 times rated current for one minute once per hour. Obtain the permitted startup duration and repetition for the selected variant. The sheet’s statements about design standards do not independently verify certification of an ordered assembly. [1]

Editorial arithmetic: 17.5/16 = 1.09375, so the tabulated 40 °C current is 9.375% higher than the 50 °C value for this variant. Those two points do not establish a universal derating factor or permission to interpolate over the entire temperature range. [1]

The attenuation plot labels four impedance conditions: 50 Ω/50 Ω symmetrical and asymmetrical, 0.1 Ω/100 Ω symmetrical, and 100 Ω/0.1 Ω symmetrical. Compare the same mode, frequency and source/load impedances. A catalogue curve alone does not establish the emissions of the assembled equipment. [1]

State supply voltage, phase and neutral arrangement, load current and overload timing, cabinet temperature, drive and cable configuration, attenuation test conditions, permitted leakage, mounting and terminal requirements.

02

Check leakage current, including fault cases

LinMot specifies 18.3 mA maximum leakage under normal operation at 440 VAC/50 Hz. Its footnote says leakage could reach 5.7 times higher levels if two phases are interrupted. This is a model-specific fault condition, not a normal rating. [1]

Editorial arithmetic: 18.3 × 5.7 = 104.31 mA for that stated worst-case factor. This does not establish measured fault leakage for another model or permission to operate with lost phases. Obtain normal and fault-case data at the actual supply voltage and frequency. [1]

DOREXS and WEMC list medical or low-leakage filter ranges. A category name does not establish medical-equipment compliance or compatibility with a particular protective device. Specify the complete application and obtain the relevant assembly documentation. [3] [2]

03

Phase configuration and assembled-filter supply scope

WEMC’s catalogue distinguishes three-phase, single-phase and IEC-inlet assemblies. DOREXS separately lists single-phase, three-phase, IEC-inlet and medical ranges. Keep the phase/neutral arrangement, mounting and leakage variant attached to the actual order code. [2] [3]

The reviewed offers below include assembled AC power-line filters. Board-mounted DC input modules, magnetic cores and current transformers are different supply items. A shielded-room power-line filter may fit this electrical scope; a complete shielded room does not.

04

Ask for a low-leakage version where RCDs protect the circuit

Schurter describes FMBC LL as a low-leakage, two-stage three-phase series suitable for applications with RCDs. Its sheet covers 7–180 A at 50 °C and 520 VAC, 50/60 Hz. Leakage is tabulated at 400 VAC/50 Hz according to IEC 60939-1: 4.3 mA for 7–55 A variants, 17.5 mA for 75/100 A and 19.3 mA for 130/180 A. The series description is not a universal RCD compatibility statement. [4]

The sheet lists 1.5 times rated current for one minute per hour and 2-second dielectric tests above 2.25 kVDC line-to-line and above 2.7 kVDC line-to-PE. Its −25 to +100 °C range is accompanied by derating information; use the selected variant’s permitted current at the actual temperature. [4]

The 16 A examples show 4.3 mA at 400 VAC for Schurter and 18.3 mA at 440 VAC for LinMot. These are different supply conditions, so the raw ratio is not a controlled comparison. Obtain data at a consistent voltage, frequency and test method. [4] [1]

Review the complete installation with the equipment and protective-device suppliers: filter, drive, cables, supply arrangement, leakage waveforms, transients and fault cases all matter. Comparing an estimated steady leakage total with an RCD trip-current number alone does not establish compatibility. [4] [1]

05

Chokes, line capacitors, earth branches and enclosure

LinMot’s schematic distinguishes coupled chokes, Cx capacitors between phase conductors and Cy branches toward earth. This functional breakdown covers the principal assembly parts; it is not a universal circuit or a production bill of materials. [1]

06

Continuous ratings, insulation tests and mounting envelope

Use the model’s stated units and test conditions. Continuous ratings, brief insulation tests, environmental qualification and physical dimensions describe different constraints.

07

Send the supply, equipment and leakage data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Supply: [voltage; phases; 3-wire/4-wire; frequency]
Load: [equipment; current; overload; cable length]
Environment: [cabinet temperature; IP]
Leakage: [limit; earth arrangement; RCD]
Performance: [standards; attenuation curves; test conditions]
Mechanical: [mounting; terminals; dimensions]

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