EMC guidelines
The following guidelines are intended to help vehicle manufacturers to meet the requirements for
Electromagnetic Compatibility. Any high speed switch is capable of generating harmonics at
frequencies that are many multiples of its basic operating frequency. It is the objective of a good
installation to minimise, contain or absorb the resultant emissions. All wiring is capable of acting
as a receiving or transmitting antenna. Arrange wiring to take maximum advantage of the
structural metal work inherent in most vehicles. Link vehicle metalwork with conductive braids.
CAUTION: It is the responsibility of the vehicle manufacturer to ensure compliance of the vehicle
to all applicable EMC standards.
General measures
Power cables
Route all cable within the vehicle framework and keep as low in the structure as is practical - a
cable run within a main chassis member is better screened from the environment than one
routed through or adjacent to an overhead guard. Keep cables short to minimize emitting and
receiving surfaces. Shielding by the structure may not always be sufficient - cables run through
metal shrouds may be required to contain emissions.
Parallel runs of cables in common circuits can serve to cancel emissions - the battery positive
and negative cables following similar paths is an example. Tie all cables into a fixed layout and
do not deviate from the approved layout in production vehicles. A re-routed battery cable could
negate any approvals obtained.
Keep power cables at least 300mm from signal cables.
Signal cables
Keep all wiring harnesses short and route wiring close to vehicle metalwork. Keep all signal wires
clear of power cables and consider the use of screened cable. Keep control wiring clear of power
cables when it carries analogue information - for example, accelerator wiring. Tie all wiring
securely and ensure it always follows the same layout.
Controller
Thermal and EMC requirements tend to be in opposition. Additional insulation between the
controller assembly and the vehicle frame work reduces capacitive coupling and hence
emissions but tends to reduce thermal ratings. Establish a working balance by experiment.
Document the complete installation, in detail, and faithfully reproduce on it all production
vehicles. Before making changes, consider the effect on EMC compliance. A simple cost
reduction change could have a significant negative effect on the EMC compliance of a vehicle.
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