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simulate this circuit – Schematic created using CircuitLab Figure 1 and 2. showing the danger of earthing through neutral. In the first example the Lunatic 'Lectrician has 'grounded' the lamp case by connecting it to the neutral wire. All appears OK although the customer notices a slight tingle when she touches the lamp when it is switched on. This ...


56

You can't float everything without an isolation transformer - the neutral will be connected to ground at the entry into the building. For safety any class I equipment does need to remain grounded, in my lab I have an isolation transformer only for the equipment under test, the scope and power supplies still have the case grounds, and are tolerant of the ...


53

If your ground strap has a proper current limiting resistor, then you would be perfectly fine connecting it directly to ground. If your ground strap does not have a resistor, then it greatly increases your chances of dying if you connect it directly to ground. If you don't have a resistor in your ground strap, and you touch a live wire while wearing your ...


51

There are four reasons for grounding the neutral. 1. Grounding neutral provides a common reference for all things plugged into the power system. That makes connections between devices safe(r). 2. Without a ground, static electricity will build up to the point where arcing will occur in the switchgear causing significant loss in transmitted power, ...


49

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

Talk with the spacecraft designers, they have to have someone coordinating electrical specs for on board equipment and you will probably need to meet their specifications.


42

The Fire Dept is wrong - it is perfectly normal to plug a device with a 2-pin plug into a 3-hole socket. Breaking the ground pin off a 3-pin plug, then plugging that into a 2-hole or 3-hole socket may produce an electrical hazard - possibility of a shock. If a high-current load, like an electric heater, was plugged into that burned outlet, and the contacts ...


39

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 ...


37

Oscilloscopes usually require significant power and are physically big. Having a chassis that size, which would include exposed ground on the BNC connectors and the probe ground clips, floating would be dangerous. If you have to look at waveforms in wall-powered equipment, it is generally much better to put the isolation transformer on that equipment ...


33

Your placement is fine. Your routing of the crystal signal traces is fine. Your grounding is bad. Fortunately, doing it better actually makes your PCB design easier. There will be significant high frequency content in the microcontroller return currents and the currents thru the crystal caps. These should be contained locally and NOT allowed to flow ...


32

Components are damaged by two or more of their pins being at a large enough potential difference. If the component has a conductive case, or pad, then that counts as a 'pin' too. It's possible to break them by trying to charge them up to a new potential through one sensitive pin, while the voltage of the other pins is held more or less constant through ...


31

WARNING: Means of being less likely to die or to kill others is discussed below. Reading may be considered useful.. Consider this "informed opinion" rather than holy writ. In an oscilloscope you want the best result you can get for the money and it's far easier to build a single ended amplifier rather than a differential one when you want ruler flat gain ...


31

Hopefully your parts are packaged in an ESD-dissipative tray or bag. Then when you set them down on your ESD mat in your lab, any charge that's built up on them can drain away through the packaging and the mat. They won't discharge quickly enough to damage the components because both the bag and the mat have substantial resistance (1 megohm to ground is ...


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 ...


26

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 ...


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

I measure 1VAC and 20mV DC between ground and my radiator. I would consider that negligible. Very likely there is a connection somewhere between your radiator and ground. It might be a long path though, for example: Radiator - pipes to central heating unit - cold water pipes (does your heater also provide warm tap water?) - cold water grounding connection. ...


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

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 ...


21

Unless there is a compelling reason otherwise, I use the same ground everywhere. You have not stated just what digital circuitry is used, but if it is modern it will very likely be fast. The way to make sure analogue and digital parts do not interfere with each other is by shaping the plane layers. This shaping applies just as much to the power rails as ...


21

If your plastic pellets are getting charged, you can flood the inside of the silo with ionized air using a commercial generator. These are not uncommon in the plastics industry.


19

You should probably connect the ground on the RPi to the enclosure for electrical shielding. If there are other experiments in the payload you should have some guidelines from the systems engineer on EMC matters. Just randomly, here is an example of what you should get (that link is for a CubeSat). For example, outgassing is particularly important if there ...


18

Without details it is impossible to give a specific answer. Look at these things closely: Grounding. This is exactly the symptom you get from a poor overall grounding strategy. Without a block diagram showing power and grounds of everything connected, it's impossible to give specific advice. However, carefully visualize all the ground return currents, ...


17

Etching PCBs at home is fun, but the process makes PCB design a bit tricky for hobbyists like us. The most important constraint is that it's difficult to make plated through-holes. And those are essential for soldering components to double-sided boards like yours. If you have your board made at a fab house, you'll get all of your PCB vias and holes plated ...


17

Digital circuits are noisy, but they can (mostly) handle their own noise without noticing. Analog circuits notice noise a lot; in fact, they have to pass noise just like a signal because they really can't tell the difference. The best way to keep digital noise out of analog circuits is to keep them separate, both physically and electrically. But they have ...


17

The 1meg resistor is needed to safeguard the user from faults from other equipment connected to mains earth. Keep in mind that the wrist strap is a permanent connection to the electric system of the building. If another piece of equipment experiences a fault, there could be a big fault current through the mains earth wiring system. That means that, in ...


17

My question is this: is this phenomenon something that truly exists, or is it simply an internal "old wives tale" with little to no basis? Well, do the math. If you sink let's say 100 A into a steel conductor of let's say 50 mm² diameter, what is the voltage over 10cm of that conductor due to ohmic resistance? So yes, Ohm's right, and if you put a lot of ...


17

Differential signaling means that there is no need for a common ground as a reference point. Also, negates the need for shielding, which is usually grounded. No DC power transfer again removes the need for a common ground and makes point #3 possible. Galvanic separation makes grounding counterproductive. Specs put considerable effort into making devices at ...


16

It makes no difference where you connect the anti-static strap to your body. The reason is that your body is much lower resistance between any two points than the strap is. Also, most of the resistance between any two points on your skin is getting thru the skin at each point. You're just a bag of saltwater (electrically, anyway). The bag has a ...


16

What you're talking about is an isolated system. I have an extended treatise on it here. In an isolated system, "the first ground fault is free" (and becomes the neutral-ground bond). This is the idea you are promoting. The problem is the second one. Unless you have maintenance staff actively doing isolation testing and chasing down and eliminating that ...


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