In a world of chaos and confusion, it is of great importance to be well grounded. This means being rooted with a strong connection to a stable foundation. Well, the same applies in the electro-mechanical world. The best laid plans can be compromised by a poor ground scheme.
Grounding sounds so simple, yet it is a very complicated thing. You get the electricity to a component or device with the proper current and voltage so everything should work as planned, right? But the problem is those electrons aren’t happy with piling up at the end of the line, they want to go home. So a return wire is required to transport them back from whence they came.
From physics we learned that a current traveling along a wire creates a magnetic field. And inversely, a changing magnetic field will cause a current in a wire. This means an induced current in a wire can adversely affect other circuits in the area by creating unwanted currents. The way to reduce the effects of all these magnetic fields is to route the return path parallel and in close proximity to the source line. This way the magnetic fields cancel each other.
In addition to these planned source voltages and currents there are several possible sources of undesirable ones. These include electrostatic discharge (ESD), radiated electro-magnetic interference (EMI) from other nearby electronic devices, and electrical short circuits due to failed insulation, cut wires, water intrusion, etc. I’m sure there are others.
For the latter, it is important to provide safety grounds from the outer chassis or any other conductive components that people can touch. If a power wire becomes disconnected or cut in an ungrounded chassis, and then falls against the chassis, the electrons will just sit there all dressed up and nowhere to go. Then along comes a technician to service the ‘dead’ device. He inserts his screw driver to remove the access panel and then he is reminded of how much he despises incompetent engineers. Safety ground connections provide a path for these undesirables to go home through a low resistance path so they are less likely to go home thru human flesh.
ESD & EMI are similar in some respects. They are not a safety hazard to the operator or technician, but they can negatively affect the function of the device and in the case of ESD, it can be destructive as well.
To protect electronics from EMI, it is best to surround them in a Faraday cage. If you want to learn more, I recommend this video from MIT physics professor Walter Lewin. The concept is to provide a layer of skin that causes the induced currents to seek their ride home on the outer shell of the enclosure and never make there way to the electronics inside.
To protect against ESD damage, it is important to ensure all conductive parts are grounded and plastics are of a static dissipative type. This will prevent ESD buildup on these parts which will eventually seek ground by arcing. Often this arc occurs in the least preferred location such as thru an expensive processor chip to a nearby mounting screw on a PCB. It is also important to provide a ground path for service technicians to dissipate any ESD they are carrying around prior to touching the innards of the device.
Now for the rub. There are just about as many grounding schemes as there are grounding concerns. Grounding terminology includes things like Isolated Ground Zone, Integrated Ground Plane, Single Point Ground, Ground Window, Star Point Grounding, etc. These different terms and approaches all have there place. But they are all intended to manage the ride home for all of these pesky little electrons in a controlled way while taking into account ground loops, magnetic fields, safety, and one more big one – surges due to things like lightning strikes. I didn’t even plan to bring this one up because it kind of turns everything upside down. A lightning strike can raise the voltage potential of the earth resulting in your ground currents wanting to reverse course and go the other direction which means your nice connection to what was once a stable foundation is no longer very stable.
For some additional reading on grounding, take a look at these:
You must be to post a comment