Control panels fail EMC and fail in thunderstorms for different reasons. Tradinor splits the RFQ. One line is the filter that has to live with the residual-current device and the leakage budget. The other line is the surge protective device that has to match the supply system and the upstream overcurrent device.
Filter first
State the working voltage, the current, and single or three phase. State the maximum leakage current to protective earth. A filter that leaks 3 mA may be normal in a machine and unacceptable on a circuit with a 30 mA residual-current device and other leaky supplies. Ask for the attenuation curve, but do not promise the machine will pass a standard because the filter datasheet looks steep. The layout, the earth bond, and the motor cable dominate the result.
- Supply: voltage, phase, and continuous current with margin.
- Maximum earth leakage at the operating voltage.
- Mounting: chassis, DIN rail, or connector style, and who wires the earth.
- For the surge device: system type such as TN-S, voltage Uc, and discharge current.
- The upstream breaker or fuse the surge device maker requires.
Do not mix the two ratings
| Device | Rating that matters | What it does not do |
|---|---|---|
| EMI filter | Current, voltage, leakage, attenuation | It does not clamp a lightning surge by itself |
| Surge protector | Uc, In or Imax, Up, system type | It does not replace a filter in an EMC test |
| Both | A note on order and lead length | A long lead undoes the clamp voltage |
Incoming check
Read leakage and voltage on the filter label. Read Uc and the system type on the surge device. Confirm the backup fuse named by the maker is the fuse you will actually fit. Do not treat a lower Up read off a different test wave as a better part unless your specification cited that wave. Keep the wiring length the maker shows. A correct part with a long loop still lets the transient through.
What to lock on the order
Show the filter and the surge device on the one-line diagram with their earth connections drawn short. The RFQ should include a sketch or a sentence that says the protective earth conductor is local and the loop area is small. Ask the filter maker for leakage at your voltage and frequency, and put that milliamp number on the order. Ask the surge-device maker which backup fuse they tested, and put that fuse on the same order so it cannot be value-engineered later. If the panel must pass a named EMC standard, say the standard and say that the filter is only one part of the build. Do not write the filter part number as if it were a certificate for the finished machine. File the datasheets with the revision of the layout you actually built.
Questions buyers actually ask
Will any mains filter pass EMC?
No. A filter is chosen for the current, the voltage, and the attenuation at the frequencies you fail. The test report is on the finished machine, not on the filter alone.
Why does leakage current matter?
Y capacitors dump current to earth. Medical and some residual-current devices cannot accept a high leakage. Write the maximum leakage at your voltage.
Is a surge protector a filter?
No. A surge protective device clamps a transient. A filter attenuates continuous noise. Many panels need both, on purpose, with a coordination note.