RFI and EMI Filters

RFI/EMI Filters Recommended Installation Practices

Minimum order qualities required for the single phase product line. Three phase products can be used for single phase application. Please contact MTE for details.

Filter Connection

Our type “RF2” and “RF3” filters are intended for use at the input side of an adjustable speed drive or inverter. Do not attempt to use these on the output (load side) of an inverter or drive. Good wiring practices will minimize RFI problems.

  • Route all conductors as close to the panel as possible
  • Physically separate the filter input and output conductors
  • Keep drive input and output leads separated
  • Always keep power and control wiring separated
  • Use shielded wiring where possible
  • Use single point grounding (connect system ground to filter)

Connect the incoming power conductors to the “Line” side terminals of the filter. Connect the “Load” side terminals to the line reactor or drive input terminals. Note that the ground termination “G” may also be designated by “E” or “N”. Keep all wiring as close as possible to the grounded panel (ground plane).

Filter Mounting

Connect the power system ground (earth connection) directly to the filter ground (earth) termination prior to connecting any other wires. Filter grounding is required to assure safety and desired filter performance. For the best ground connection, use a multi stranded copper conductor or copper strap. Mount the filter as close as possible to the RFI/EMI source (drive, inverter, UPS, etc.). For best performance, mount filter directly to a bare metal grounded panel. Use shielded conductors to minimize radiated high frequency noise levels.

Current Ratings

The “RF” series filters are rated in True RMS (trms) amperes. Harmonic current distortion will increase the trms current of a system above the fundamental current (typically motor FLA) of the connected loads. Line reactors (3% or 5% impedance) are useful
in reducing harmonic current distortion and the trms current. If minimum 3% impedance line reactors are included in the installation,
then the trms amperes will be lower and the filter can be sized for the reduced load current.

If you know the trms amperes of the load to be connected to the filter, then select the filter directly from the RMS amperes selection tables. If you are not sure of the trms amperes, you can select the filters based on the horsepower (or KW) rating of the load to be connected. Determine if a reactor (minimum 3% impedance) will be used in addition to the RFI filter and select accordingly.

Parallel Connection for Higher Ratings

Type “RF” filters may be connected in parallel to achieve higher current ratings provided that identical models are used, and the connection allows each individual filter to share current equally. The use of two separate distribution (terminal) blocks will make this easier. Derate each filter by 10% when ever connecting in a parallel configuration and always follow the NEC or local electrical codes.

Make ground connections first, then for each filter to be parallel connected, precut three leads, of equal wire type and gauge, to the same exact length.

Using these leads, connect the filter input terminals L1, L2, and L3 to the respective terminal on a separate distribution block. Repeat this procedure for the output terminals.

Typical drive and inverter applications include:

  • AC Motor Drives
  • DC Motor Drives
  • Uninterruptable Power Supplies
  • Active Harmonic Filters