types of grounding....

Discussion in 'General Electronics Chat' started by antennaboy, Oct 1, 2011.

  1. antennaboy

    Thread Starter Active Member

    Jan 31, 2008
    Helllo Everyone,

    question about grounding. I understand that in DC circuit the choice of the reference point is arbitrary. That arbitrary point is also called chassis ground. If that point is physically connected to planet Earth then it is called Earth ground.

    I have recently heard about "ground signal"...What is it?

    Also, why in some circuits we use multipoint grounding? Is good for both AC and DC?

    For instance, in a car, the negative terminal of the battery is connected to chassis. All the other components that are grounded are multipoint grounded?

  2. colinb

    Active Member

    Jun 15, 2011
    “Signal ground” would the ground for most digital circuits, for instance.

    Chassis ground is often used in electrical device for safety reasons and to reduce electromagnetic interference (EMI) emission from the device (an ungrounded metal chassis could couple internal signals and act like an antenna to radiate noise). For safety reasons, the chassis of line-powered appliances is normally required to be grounded to earth ground (a protective ground) this way, if a fault occurs within the device causing line voltage to be shorted to the chassis, a circuit breaker will blow -- if the chassis was ungrounded (floating), then the chassis could silently remain at high voltage potential until a human touched it and created a path for current to flow to ground, resulting in dangerous electric shock.

    In a vehicle, many devices use the chassis as the power return conductor. For instance, my headlight bulb in my car have only one wire connecting to them. The metal flange on the bulb is the ground side of the bulb and connects to the vehicle frame, which is used as the path back to the battery.

    Multipoint grounding might be used for different reasons in different situations. It needs to be used cautiously to avoid ground loops, which can result in significant currents flowing through wires not intended to carry such currents.

    Grounding systems are much more complex than one might expect! For instance, there is a lot of debate about the best way to implement grounding systems on USB devices: should the USB cable shield be connected to the signal ground at the USB device? If so, is it directly connected? Or is it connected through a high-value resistor? Through a capacitor+resistor?
  3. #12


    Nov 30, 2010
    We've seen this kind of question a dozen times. I could write 500 words on this subject and only have half the information.

    1) Ground is often a reference point that is declared ground because it is convenient.
    2) The word, "ground" probably started as Earth Ground because of early radio work.
    3) "Ground" is used for AC, DC, signals, and safety connections. Because of this, it can get really complicated. One machine can have a chassis ground connected through the "bond" wire to the planet, a circuit ground for a circuit board, an isolation transformer or an opto-coupler to another circuit board with yet another circuit ground, and the neutral current carrying conductor on the power line that is almost at ground potential except for the resistance of the copper wire and the current floing through it causing a voltage on the line.

    A car chassis is usually called ground, and the voltage on American cars is positive with respect to the chassis.

    Star grounds are used to keep high speed pulses on their own conductor so they don't disturb the ground for the analog circuits.

    Is that 500 words yet? I know I'm only half done!
  4. Wendy


    Mar 24, 2008
    The term ground is very generic, and gets people in trouble because of it. You talk to someone who is into electrical work they will be adamant about what it is. This is because it is a safety issue, a major one.

    Talk to a tech or engineer who work with electrical circuits they will acknowledge the safety aspects of ground, but then talk about something else that they happen to call ground. It drives the electricians and maintenance guys nuts.

    Antennas need a ground too, and it is not quite the same as the first two, but has relationships in both. A ground for an antenna is a electron sink, something you can pull surplus electrons or dump extras into. This is because in an antenna there is an actual surge of electrons, bouncing back and forth, in resonance to the length ideally. This unique current flow generates electromagnetic waves, which is why an antenna that is tuned to a specific frequency works best. It is also reversible, the electromagnetic radiation causes the current surge bouncing back and forth in the antenna.

    RF is what got me into electronics. You can spend a long time studying antennas and RF theory. It was one of my core subjects when I went to college.