Control Unit (CU-4E-FMH) EMC Considerations

This article ensures that the use of the CU-4E control unit complies with applicable regulations for Electromagnetic Compatibility (EMC).

Luminaire design engineers, electrical contractors, Enlighted field applications engineers, and Enlighted sales personnel can use this Application Note to understand when EMI (ElectroMagnetic Interference) control measures are required to ensure EMC (ElectroMagnetic Compatibility) compliance.

Overview

The CU-4E was designed to meet FCC “Class A” (Industrial and Commercial) EMC limits.  While the intention was for CU-4E to service the same markets worldwide, the European requirements for these markets are more stringent.  Many other countries outside of North America follow the European EMC Limits. The CU-4E, by itself, will likely not pass the European EMC Limits.  However, additional external filtering can be provided in the luminaire to ensure that the complete installation is compliant to these more stringent EMC requirements.

All installations outside of North America should consider the guidelines presented in this document.

There are two types of EMI that are of concern to the regulatory authorities, Conducted EMI which travels over the wiring and Radiated EMI which travels through space without wires.  Both types of EMI must be evaluated by testing the complete luminaire.  The relevant standards for EMC outside of North America are:

  • IEC61000-6-1 Immunity standard for residential, commercial and light-industrial environments
  • IEC61000-6-3 Emission standard for residential, commercial and light-industrial environments
  • IEC/EN55015 Limits and methods of measurement of radio disturbance characteristics of electrical lighting and similar equipment

The decision on which standard(s) to evaluate luminaire compliance against is up to the luminaire manufacturer and should be stated in that manufacture’s Declaration of Conformity (DoC) document for the luminaire.                               

Conducted EMI

A conducted EMI filter must always be installed when using the CU-4E-FMH in a region that requires compliance with IEC61000-6-1 or EN55015.  Conducted EMI filters are commercially available in many physical shapes and sizes.  Electrically they are connected between the AC power input (mains) and the CU.  They are most commonly packaged in a metal “can” enclosure with screw mounting tabs and for electrical connections have wire leads or terminals (for slip-on connectors) as shown in the photograph on the right.

The selection criteria for the filter is primarily based on physical size and current handling capacity.  The filter should provide at least 10dB of common-mode attenuation in the 150kHz to 450kHz frequency range.   The current rating of the filter should be based on the requirements of the LED driver load connected to the CU-4E as well as the operating temperature requirements.  Note that many filter manufacturers will ‘de-rate’ the current carrying capacity of the filter at higher ambient temperatures.

The EMI filter that has been evaluated and tested by Enlighted for use with the CU-4E is the Delta 05DBWA5, which is rated at 5A load, equivalent to the CU-4E maximum load rating.  A smaller filter such as the 02DBAW5, rated at 2A load, could be used if there are space constraints within the luminaire.  The wiring connection for the filter is shown in the following diagram (Drawing #93-02744-01):

Radiated EMI

Radiated EMI filters may or may not be required, depending on the routing and length of the luminaire’s internal wiring. For field installed retrofits the use of a radiated EMI filters is recommended since no additional EMC testing is being performed and the installation of the CU-4E may put the installation out of compliance.  For OEM manufactured luminaires, the need for radiated EMI filters can be based on the laboratory test results of the unit being evaluated.

Radiated EMI filters are commercially available in many physical shapes and sizes.  They are referred to as ‘ferrite absorbers’ or ‘ferrite cable cores’.  Physically the wires that are to be filtered are placed through the hole in the core.  More than one conductor can be routed through the core. If more attenuation is required, the conductors can be looped through the core more than once.  Cores are available in a split “snap-on” configuration so that they can be added after the wiring has been put in place, rather than needed to thread the wires through the hole in the core.  See the photograph to the right.  The physical size of the core will be dependent on the number of conductors routed through the core.  The RF properties of the core should be such that it provides significant attenuation at lower frequencies (under 100 MHz).  Various manufacturers use different designations for their core material, but all will specify if the material is intended for lower or higher frequency applications.  The physical size of the core is dictated mostly by the diameter of the hole needed to pass all conductors through without the possibility of pinching the wires.    Suggested products include those based on the Fair-Rite 31 type core material, Fair-Rite part number 0431167281 or Laird 28 type core material, Laird part number 28A0807-0A2.

All conductors from the CU-4E that exit the luminaire enclosure should be routed through a ferrite core.  At a minimum, these would be at least the mains connection wires routed through a single core.  If the sensor is external to the luminaire, the sensor cable should be routed through a ferrite core.   Similarly, if the driver is external to the housing containing the CU, then the driver wires (both AC power and dimming control) should also be routed through ferrite cores.  Multiple conductors can be routed through a single core, but it is recommended that conductors with mains potential voltages be kept on a core separate from conductors with Safety Extra Low Voltage (SELV) levels. This is because the two groups of wires are physically on opposite ends of the CU-4E, so wire length before the core is minimized, and to protect against possible shorting of mains voltage to the SELV wires in the event of insulation damage.  Some regions may prohibit having mains and SELV wires in close contact, so any such restrictions should be verified if attempting to use a single core for all filtering.

The ferrite cores should be located as close as practical to the CU-4E.  An example of how the cores might be placed in the wiring compartment of a luminaire is shown in the photograph below.  Note that in this example the driver is in a separate compartment, and the sensor is external to the luminaire. 

Suggested Placement of EMI Filter and Ferrite Cores

 

 

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