California Department of Transportation
 

7. ELECTROMAGNETIC INTERFERENCE

  1. Good means of suppression are:
    • Resistors
    • Capacitors and inductors
    • Interference suppression filters
    • Ferrite cores
    • Special wiring and connections
    • Shielding
    • Diodes
    • Grounding
    • Separation between devices, rerouting
  2. The amount of suppression and type needed depends on the vehicle and source of interference (e.g., computing devices, radio transmission, cell phone, motors, coils, etc.).
  3. Electronic items that may be sensitive to interference shall have their wiring run separately from other wiring or be shielded and grounded. Signal, data, control, and other low power conductors shall not be placed adjacent to DC power conductors.
  4. The three types of electromagnetic propagation that must be dealt with are:
    • Radiated electromagnetic fields (radio transmitters)
    • Conduction. Physical connection between two devices close to each other, through wire and cable
    • Induction. Induced signal by either magnetically or capacitive coupling from one conductor to another.

    It is up to the installer or builder to address these and find the best method of suppression.

  5. Wiring from engine instruments, electric motors, solenoids, alternator outputs, ignition systems, DC to AC inverters, electric fuel pumps, fluorescent lighting can cause noise problems.
  6. If wiring can’t be separated to keep it from noisy wires then shielding or suppression are required.
  7. Electrically operated equipment both installed and portable shall comply with interface standard requirements for the control of electromagnetic interference of subsystems and equipment.
  8. When the engine is being started no electronic device shall be on unless the device is on an isolated circuit.
  9. When auxiliary electrical systems are added they must have no EMF effect on the vehicle.
  10. Equipment containing a DC electric motor must have a blocking diode installed to prevent back EMF. If the motor is driven by a relay or solenoid then the solenoid/relay coil shall have the blocking diode.

Last updated 01/14/04