Hot answers tagged

54

The first time I tried to do the current calculation for a circuit similar to the previous circuit on a simulator, the program complained about not having a ground and "floating voltage sources". Your simulator wants to be able to do its calculations and report out the voltages of each node relative to some reference, rather than have to report the ...


51

Good layout and grounding seems to be poorly understood out there so religion finds a foothold. You are right, there is really very little reason to use both the top and bottom of a two layer board for ground. What I usually do for two layer boards is to put as much of the interconnects as possible on the top layer. This is where the pins of the parts are ...


48

Sometimes people get confused just by the many definitions of the word. ground noun the solid surface of the earth; firm or dry land: to fall to the ground Often, grounds. the foundation or basis on which a belief or action rests; reason or cause: grounds for dismissal. In the context of electronics, sometimes ground means sense 1 above. Earth is, after ...


48

If you just ignore the POE 48 Volts in the image below, you can see Ethernet uses transformers on both sides. This way there is no need for common ground as long as the common mode voltage stays below 1500V generally. The isolation specification of the transformers. And as a bonus you now also know how POE works. (802.3at) However, CAT6A often has a ...


44

"Ground" is just a code word which, in this case, refers to the "current return common" circuit node. There is a complete circuit because everything electrical in the car, such as the starter motor, also connects to ground in order to return current to the minus terminal of the battery through the ground. The car's chassis is used for this return network, ...


38

Three reasons come to mind: 1) Take a look at this close-up of the guts of a microcontroller. There's a LOT going on in there. And every part of that die needs power. Power coming in from any one pin will probably have to snake it's away around a lot of stuff to get to every part of the device. Multiple power lines gives the device multiple avenues to pull ...


33

You got to think in terms of shared impedance (not resistance, really impedance). Consider the parts of the circuit that use GND as a 0V reference for sensitive analog purposes. Obviously you want each of these "0V references" to be at the same "0V" potential. However current running through the GND plane will introduce an extra error voltage on top of each ...


33

Many appliances in the USA and elsewhere have two-prong plugs because they are "double insulated." The third prong is for ground fault protection except where outlets have been designed with protective shutters on the current-carrying slots that are opened by the ground prong. Double insulation provides very effective ground fault protection that is less ...


28

This is a shielding ground wire (or S-GND) which is left bare on purpose, so it makes contact with the foil. It has to be connected (crimped or soldered) to the metal casing of the USB receptacle / plug at the end of the cable. If your device includes a USB connector, S-GND can be connected to the device ground (same as GND), but this connection is optional. ...


27

Ground means whatever is attached to this symbol in the schematic: Everything that touches this symbol in the schematic is actually connected to everything else that touches the symbol. Since so many things connect to it, this makes the schematic easier to read. Usually the negative side of a battery is attached to that. But, there are many circuits that ...


27

Why is Ethernet not grounded? There are two reasons: 1. It would create a ground loop between devices 2. The device would also be more susceptible to ESD which is prevalent in cables that are being moved or handled (from triboelectric charging of the cable) The reason Ethernet is more susceptible to a ground loop is because: The loops could be much ...


27

It stops the resistance from going to infinity if there is dirt on the potentiometer track. (it just goes to max instead)


26

That is the drain wire that helps carry charge off of the foil jacket and carries more current than the foil can. It is part of the shield/ground of the cable. As far as how to terminate it, that depends on what function it serves in your system. There are several purposes for that shielding: Reducing EMI emissions Reducing EMI susceptibility Defining ...


26

You (and the some of the other answers) focus too much on the actual value of the resistance to ground; the fact is that the actual value is irrelevant regarding ESD. The ESD charge just needs a path. If that path is high-ohmic (few mega-ohms) it will only take slightly longer for the charge to find its way to ground. But it will still be a fraction of a ...


25

The main point of grounding a line-powered appliance is to electrically "box up" the dangerous parts. If, for example, a "hot" wire comes loose inside the appliance and touches the metal case, the current will flow thru the ground connection to that case. That will blow a fuse, trip a breaker, or trigger the ground fault interruptor if that line is ...


25

Consider this: You have your 1kV power supply, with an impressively insulated wire going out to a resistor. Coming back, you have a return wire with light insulation because, hey, it's grounded! Now the ground wire breaks at the power supply. Your "safe" ground wire is now at 1kV. Is that light insulation sufficient?


24

Strictly speaking, ground is a connection to the Earth. When we speak about a "safety ground", it is this kind truly earthed connection. In circuits, the "common return" path to the power supply is informally called "ground", even though it is not actually earthed. Battery-powered devices, and the electronics inside airplanes, still have grounds. All ...


23

Ground planes in general are almost always a good thing, but if used incorrectly can actually hurt the quality of your board. A typical board like you have here would have 1 layer dedicated to be a ground pour only with no traces running on it. However, it sounds like you are wanting to make your top layer have a ground pour so that you don't have to remove ...


23

2) I highly recommend AGAINST cutting ground anywhere near high-speed signals. Stray capacitance really doesn't have too much of an effect on digital electronics. Usually stray capacitance kills you when it acts to create a parasitic filter at the input of an op amp. In fact, it is highly recommended to run your high-speed signals directly overtop of an ...


22

Cables FL1000B20-WHT and FL1000B20-BLU are twisted pair with additional shield. Look at these symbols:


21

Your schematic is excessivly large and layed out in a confusing way, which discourages people from responding. Don't draw grounds going upwards, for example, unless the parts really are coming from a negative voltage. If you want others to look at a schematic, give them some respect. Don't make us tilt our heads to read things and make sure text doesn't ...


20

There are no guarantees. Earthing systems will be worked out on the basis both of theory and of empirical results gained from long experience. The earth that you describe is extremely impressive, and far superior to what I have seen in some other standards. Grounding does NOT ensure personal safety Note that while personal safety is invovled in grounding ...


20

Voltage is not an absolute value. It's pointless to say they're grounds and therefore are the same. It's like suggesting that I'm five miles away from New York and you're nine miles, therefore I just need to walk four miles to get to you. Except it's even worse than that, because that's a reference point, it's more like saying I'm five miles from my ...


20

Problems: First, currents don't "come from" the positive terminal. That's a very common misconception, called the "sequential fallacy" in grade-school electricity textbooks. The basic problem is that wires are not like empty pipes. And, the power supply doesn't fill them up. Instead, wires are already pre-filled with charge, so that currents always ...


20

                                         IEC No. 5017, better known as Earth Ground, is the result of many over a 100 years of organic evolution, convention, and most ...


19

Voltage is relative. One voltage level only makes sense if you have another voltage level to compare it to. If you would look at the signal wire alone you wouldn't get any wiser, you wouldn't measure a voltage. You need a reference to measure against, so that you can say that the signal is so-and-so-many volts, referenced to ground. That referenced to ...


19

Combining digital and analog grounds is quite a contentious issue, and is might well fire up a debate/argument. A lot of it depends on whether your background is analog, digital, RF etc. Here is some comments based on my experience and knowledge, which is likely to differ from other peoples (I am mostly digital/mixed signal) It really depends on what kind ...


19

If wires were 100% reliable and had zero resistance, there would be no difference between the neutral (groundED conductor) and the safety ground (groundING conductor). Neither condition applies, however. Even if the neutral-grounded and safety-grounding conductors are connected at the breaker panel, a current-drawing appliance some distance from the box ...


19

Voltages do not have a "universal" reference frame. A voltage is also known as a "potential difference", meaning that a voltage is just the difference between two points. So they can reference to any other voltage. Engineers can work on a 400,000V cable if they don't connect to ground; indeed they are sometimes in a cage hanging from the overhead cable, ...


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