Many automotive EMC problems are attributed to “bad ground” connections. Bad ground seems to be the cause of many problems in all types of electrical circuits. The reason that there are bad ground connections is simple. There is not a “ground” anywhere on a vehicle! The reason there is no ground connection is also simple. The vehicle is intended to travel on the ground, not attached to it. Actually, the one time when there can be a ground connection on a vehicle this is shown in Figure : In this case, if the ground connection is maintained, it can be seen. | This page intentionally left blank TLFeBOOK Chapter 3 Power and Signal Return INTRODUCTION Many automotive EMC problems are attributed to bad ground connections. Bad ground seems to be the cause of many problems in all types of electrical circuits. The reason that there are bad ground connections is simple. There is not a ground anywhere on a vehicle The reason there is no ground connection is also simple. The vehicle is intended to travel on the ground not attached to it. Actually the one time when there can be a ground connection on a vehicle this is shown in Figure Figure . Vehicle With Ground Connection In this case if the ground connection is maintained it can be seen that the vehicle is of little use as a transportation method if it can only travel as far as the ground cable allows it. The use of the term ground unfortunately has become used to describe the path where the return currents are assumed to be flowing. As a matter of fact there is a circular definition of the term electrical ground. Many writings on electrical circuits refer to the ground as the sink of the power or signal currents . That definition MAY be satisfactory if the return currents read this definition and then consult with the circuit designer to find out where they should be flowing There are interesting definitions that have TLFeBOOK 18 Automotive EMC been developed. One heard recently was the concept of dirty and clean grounds. This emphasizes the fact that a ground is not what it is supposed to be since we seem to keep making more definitions when realize when our existing ones do not work It is correct to look at the path of the return currents as the return . Doing so will eliminate the underlying assumptions about ground connections that are not always true. For example it is sometimes assumed that the ground is a zero impedance path and can sink infinite amounts of current. The problem is that in the real world there is no such thing as zero impedance and there is .
