Line Noise

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RFI from Light Dimmers

The following is an excerpt from lutron.com

WHAT IS RADIO FREQUENCY INTERFERENCE (RFI)?

RFI is a buzzing noise which may occur in some audio and radio equipment when solid-state dimmers are used nearby. Although every Lutron dimmer contains a filter to suppress RFI, additional filtering may be required in some applications. Typical examples of RFI-sensitive equipment are AM radios, stereo sound systems, broadcasting equipment, intercom systems, public address systems, and wireless telephones.

RFI can be transmitted in two ways: * Radiated * Conducted

Note: The suggestions in this application note will help minimize RFI: however, they do not guarantee that RFI will be completely eliminated.

Radiated RFI

Any sensitive equipment that is in close proximity to dimming equipment can pick up the RFI and generate noise into its system.

The following are three possible ways to minimize the radiated RFI:

• Physically separate the RFI-sensitive equipment from the dimmer and its wiring.
• Run dimmer wiring in its own metal conduit.
• Use a lamp debuzzing coil (available from Lutron) to filter the RFI.

Conducted RFI

In some cases, RFI is conducted through the building wiring and directly into the AC power supply of the sensitive equipment.

To minimize the conducted RFI, follow these guidelines:

• Feed sensitive equipment from a circuit without a dimmer on it.
• Add a power-line filter to the sensitive equipment.
• Add shielded wire for all microphones and input cables. Also, use low-impedance balanced microphone cables, which are less susceptible to interference than high-impedance types.
• Make sure all the equipment is grounded. Connect all shields to the ground at one point. Ground lighting fixture metal housings properly.
• Use a lamp debuzzing coil (available from Lutron) to filter the RFI. Lamp Debuzzing Coils Lamp debuzzing coils (LDCs) are the most effective way to reduce RFI. One LDC is required for each dimmer. Select the LDC according to the connected lighting load. The LDCs may be wired in series on either the line side or the load side of the dimmer. For maximum RFI suppression, keep the wiring between the LDC and the dimmer as short as possible.

Since the LDC itself make an audible buzz, mount in a location where the noise will not be objectionable (e.g., an electrical closet, a basement, or above a drop ceiling). LDCs are designed to easily mount onto a standard 4"x4" junction box. They are UL listed and thermally protected.

The following LDCs are available from Lutron: Model # LDC-10-TCP LDC-16-TCP Rated Capacity: 600-1200W 1201-1920W.

See also: Ground Loop

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