Understanding Grounded Electricity

[FinalAvenger]

"Grounded" Electricity

Well I've checked a few sites for the answer but I still don't seem to understand the grounding as well as I'd like to. I understand that it literally means a wire that goes into the dirt. What I don't understand is where the electrons go after that. Or what they are doing in a socket before you plug something in.

Lets say we were talking about water. If you "grounded" water, it would just sit there and get soaked up and eventually go away. When you arn't using a spicket, the water is sitting there waiting to be used. But before you plug something in, is the electricity sitting there at the end of the wire or is it moving elsewhere? Thanks.

 

[rayjohn01]

Grounding allows a current ( temporary) to flow between the object and ( Earth , water pipe, etc.) IF there were a voltage between them -- like discharging a capacitor,
This ensures that the volt difference is close to zero to eliminate accidental shock.
The Main AC supply has one conductor close to ground ( third prong) it is this one which must be used for internal 'grounding of cases etc. , but in many instances there is no ground wire( two prong) but one is close to ground potential.
Don't play around with this if your not sure.
Grounding of RF equipment has to do with antennas, the Earth acts like a large slightly imperfect mirror and vertical antennas form half the total ( the mirror the rest ) which is why many such antennas are 1/4 wave as opposed to what they should be 1/2 wave. ray.

 

[chroot]

Ordinarily the ground wire does absolutely nothing. No electrons flow through the ground wire at all under normal circumstances. Remember that only a few decades ago plugs only had two prongs, with no ground.

The ground wire is important only for safety reasons. I'll quote from howstuffworks.com:

The idea behind grounding is to protect the people who use metal-encased appliances from electric shock. The casing is connected directly to the ground prong.

Let's say that a wire comes loose inside an ungrounded metal case, and the loose wire touches the metal case. If the loose wire is hot, then the metal case is now hot, and anyone who touches it will get a potentially fatal shock. With the case grounded, the electricity from the hot wire flows straight to ground, and this trips the fuse in the fuse box.

http://electronics.howstuffworks.com/question110.htm

- Warren

 

[rayjohn01]

Actually 'ground wires' are quite active they are subject to induced voltages from nearby equipment - radio waves , static electrical discharges , lightning and so on -- there is no such thing as a perfect ground , and some 'ground wires have enough voltage to give you a shock -- not usually lethal tho'. Ray

 

[chroot]

What you've said about ground wires is true for all wires. Although true, it's not particularly relevant to the discussion.

- Warren

 

[rayjohn01]

You can choose to ignore , but in my opinion we are talking about the meaning of grounding and what a ground wire is like I believe is relevant.
If youve ever seen the result on equipment of a ground surge you may think differently.
It is not always true that active wires are treated in the same way as ground wires hence they can be subject to very different conditions. Not only that but you cannot assume all wires are balanced to common mode surges which are often ground induced without connection.
How many other topics would you like to ignore . Ray.

 

[chroot]

rayjohn,

The original poster simply asked what a ground wire is intended to do -- that question has been answered. Please stay on-topic. Advanced topics like lightning-strike induced ground surge and RF interference just aren't relevant here.

- Warren

 

[FinalAvenger]

Ordinarily the ground wire does absolutely nothing. No electrons flow through the ground wire at all under normal circumstances. Remember that only a few decades ago plugs only had two prongs, with no ground.

The ground wire is important only for safety reasons. I'll quote from howstuffworks.com:


http://electronics.howstuffworks.com/question110.htm

- Warren

From 2 pm to about 2 in the morning yesturday, all I was doing was reading electricity articles on HSW haha. It's so interesting and of course I read that article as well. But I was just thinking that it seems electricity needs to go in a "circuit" but when it goes to the "ground.".. Where's the circuit in that? Does it just go and disperse the electrons in the dirt?

 

[Njorl]

From 2 pm to about 2 in the morning yesturday, all I was doing was reading electricity articles on HSW haha. It's so interesting and of course I read that article as well. But I was just thinking that it seems electricity needs to go in a "circuit" but when it goes to the "ground.".. Where's the circuit in that? Does it just go and disperse the electrons in the dirt?

There's a saying in circuits, "Grounds of the world unite".

So, if you see a circuit diagram with a power supply and a device, and the hot side of the supply goes to the device, and both the supply and device also go to ground, there is a circuit, because the grounds are considered shorted to each other.

Beware though. In practice, grounds can have slight differences. It isn't enough to hurt anybody, but if your measuring small AC signals, ground loops can ruin hours of data.

Njorl

Njorl

 

[megashawn]

Lemme take a crack at it.

Think of an automobile. Think of the charging system. Generally, the battery which has a positive and negative, has two connections. The negative terminal is attached to the chassis of the car, while the positive connects to all the various powered items.

If you were to take a light bulb, attach a wire to one terminal on the bulb, and the other end of the wire to the positive, nothing would happen.

Now, touch the second terminal of the bulb to any metal part of the automobile and current flows from the battery, through the chassis, and into the bulb.

In this case, the chassis of the car is considered grounded, although it is not connected to the ground. Grounding is basically a term, and while yes homes generally have a ground point somewhere that is planted in the earth, as was mentioned, this is merely for safety purposes.

Now, a neat trick is to find a nice healthy tomato plant and a multimeter, plug the positive probe of the meter into the plant, somewhere near the top, and put the negative probe in the dirt. Set the multimeter to measure low dc volts, and you should see some numbers, representing the voltage present in the plant.

It isn't like every electrical device is plugged into the ground, it is more like a method of requiring less wire/circuit traces. In an automobile, and DC device can be powered simply by attaching a positive wire to it, and another which is attached to any bare metal.

Consider a car stereo. You run a power wire, usually from the fuse box, but we will say from the positive of the battery. Now, if your antenna is properly installed, it serves two purposes. One is to pick up radio channels, and the other grounds your stereo to the chassis of the car. This completes the circuit and allows you to power on your stereo.

Some of the older, cheaper stereos out there use a thing that is called "Common Grounding" And a two speaker stereo system will only have 5 wires, 1 power(positive), 1 ground(negative), Right speaker positive, left speaker positive, speaker ground.

In this case, you would install the stereo as I mentioned above, you can attach the ground wire for extra elimination of road noise if needed. To install the speakers, you run one wire from the Left + and one from the Right + to the respective speakers. Then, you can run a single wire to both speakers.

 

[chroot]

Car stereos are not grounded through the antenna.

Running speaker return current through the chassis is a guaranteed way to make your stereo sound like crap.

- Warren

 

[rayjohn01]

Chassis

Megashawn
you sometimes also see a wire trailing under the car to scrape the 'ground' this is literally to ground the car chassis since in dry weather it can build up static of 10's of thousands of volts giving quite a sharp shock on leaving the vehicle. Here the car and the real ground act as a capacitor -- the wire discharges it by conducting electrons from one to the other . Ray

 

[Njorl]

Megashawn
you sometimes also see a wire trailing under the car to scrape the 'ground' this is literally to ground the car chassis since in dry weather it can build up static of 10's of thousands of volts giving quite a sharp shock on leaving the vehicle. Here the car and the real ground act as a capacitor -- the wire discharges it by conducting electrons from one to the other . Ray

I remember as a kid, all the cars and trucks had them. Now, I almost never see them. I live in DC, where it is not dry at all (it is a stinking swamp). Do they have them in drier areas still?

Njorl

 

[rayjohn01]

Brrrr

To Njorl
I live in Canada Njorl where it varies from being hot and humid to being cold and very dry. Yes they still use grounding wires as the shocks can be really sharp , one trick is to use a Key to touch the metal rather than a finger. :surprise:

 

[Gokul43201]

Beware though. In practice, grounds can have slight differences. It isn't enough to hurt anybody, but if your measuring small AC signals, ground loops can ruin hours of data.

Njorl

I concur ! Establishing "true" single point ground can be a real hard problem to solve. We had to spend weeks redigning/implementing our grounding scheme because of picovolt noise that came from someone buying soda from the coke machine behind our lab.

 

[megashawn]

Car stereos are not grounded through the antenna.

I can assure you the car stereo I'm using right now begs to differ.

 

[chroot]

I've never had one grounded through the antenna and I've installed probably a half-dozen. Weird.

- Warren

 

[megashawn]

I've installed a lot myself. Consider this.

The antenna body is metal, more times then not. It threads into the car, also metal. The car, being grounded itself grounds the antenna. The outside metal of the antenna is connected to the part of the antenna which is grounded to the car.

You don't even have to plug the antenna into ground the stereo. Touch the ground wire of the stereo to the outside of the antenna, or the outside to the chassis of the stereo.

This comes in handy especially in newer cars where everything is plastic and it is hard to find a good ground point.

 

[chroot]

Hmm I wasn't aware the antenna itself was grounded to the chassis.

- Warren

 

[megashawn]

Well, it is a little known trick, because 9 times out of 10 you already have the power and ground wires hooked up before you plug the antenna in.

 

[Cliff_J]

Most newer cars supply ground for the deck right in the harness. Pretty easy unless you really want to 'old school' the thing. On too many cars though, the antenna ground is near the brake light ground or what not, its just like asking for alternator whine or pops in the system if you have a lot of components.

Cliff

 

[rayjohn01]

radio input

to Megashawn
if the antenna is literally connected to the chassis ( assuming it's also metal -- then where does the radio input get connected ( it's antenna input).

 

[Metallicbeing]

Electrical Grounding System

According to the National Electrical Code, A ground shall be bonded at the electrical source (along with the grounding rod, neutral, gas and water pipes, metal structure, and foundation rebar) and maintain continuity throughout the metal parts of the entire electrical system. The NEC also states that a grounding rod shall not be the sole means of grounding.
What this means is that the grounding system is meant to be an emergency path back to the source if something "hot" were to make contact with exposed metal parts and surfaces. If you only use a grounding rod with the minimum requirements (25 ohms), it would not have sufficient continuity to trip the circuit breaker. The grounding rod is mainly a path for lightning.
Unfortunately, grounding systems that are incorrectly installed can be very dangerous. Some examples are bonding neutrals to the grounding buss in breaker panels, poor continuity throughout the grounding system, No bonding at the source (a floating ground), etc...
Electrically speaking "ground" means reference to 0 volts (ideal).

 

[PMASwork]

Megashawn
you sometimes also see a wire trailing under the car to scrape the 'ground' this is literally to ground the car chassis since in dry weather it can build up static of 10's of thousands of volts giving quite a sharp shock on leaving the vehicle. Here the car and the real ground act as a capacitor -- the wire discharges it by conducting electrons from one to the other . Ray

Yeah - I can empirically back that up!

Here in AZ, it can get very dry. I have stepped out of the car and received quite an uncomfortable shock.. plus, sometimes you accidentally brush the car with your calf or other body parts while exiting, so this nasty shock can get you in some very sensitive areas! :yuck:

 

[megashawn]

Most newer cars ...

This is true, however I am ole school and don't own a vehicle younger then 20 years old. Alot of times just using the metal straping that helps hold the stereo in place will ground it as well.

But hey, I'd had a car stereo hooked up in my bedroom before, trust me, there are millions of different configurations to hook it up. I used a pc power supply for that trick, worked like a charm.

About the alternator noise, I've never had much trouble with it. Infact, I started only using the antenna to ground because I've found I get more noise from using factory grounds then I do making my own.

Anyhow, sorry for the thread hijack :)

 

[wimms]

Car stereos are not grounded through the antenna.

Running speaker return current through the chassis is a guaranteed way to make your stereo sound like crap.

- Warren

That is true. And anybody arguing this can only beg to differ in definition of crap.

 

[megashawn]

before I go through the trouble of taking a photo of such a setup in action, will it even do any good?

I hate when people are so blinded by there "education" and "expieriance" that can't take a second to realize that maybe, just maybe there is another way of doing things.

 

[Integral]

All the car antennas I have dealt with are coaxial, there is an outer shield, which is ground, and an inner conductor, which I have always assumed is different from ground. Are you using the inner conductor as ground, or the Shield?

 

[megashawn]

You plug the antenna in, the stereo is grounded. I may have explained it incorrectly earlier, but I assure you, it works. I will post a pic of a system working if need be.

I would imagine it is the shield wire, as it is in contact with the outer portion of the plug, which contacts the chassis of the stereo.

 

[Integral]

You plug the antenna in, the stereo is grounded. I may have explained it incorrectly earlier, but I assure you, it works. I will post a pic of a system working if need be.

I would imagine it is the shield wire, as it is in contact with the outer portion of the plug, which contacts the chassis of the stereo.

If this is the case you are not grounding the antenna, the antenna is the center wire of the coaxial cable. The shield should be ground, I do not think it is wise to rely on the antenna shield as the sole ground, some systems may rely on the stereo to provide the ground to the antenna shield. (not likely but, possible)

 

[chroot]

Integral,

Hence my confusion. I thought megashawn was indicating the actual antenna itself was grounded to the chassis -- and it's not. You wouldn't be able to pick up radio waves very well at all with a chassis for an antenna. I gave up and stopped participating in the thread.

Certainly you could ground your stereo with the coax sheild, but it's still probably not a very good ground. Ideally you'd like your ground to be as close as possible to the head unit itself; the longer the wire run, the larger your likelihood of picking up alternator whine. The power wire is not very susceptible to noise, because it's regulated and filtered inside the head unit anyway. The ground wire, however, is quite susceptible to picking up noise.

- Warren

 

[chroot]

There's also a good chance that the antenna shield conductor is connected to the head unit's internal ground through a few RF chokes or other power-supply isolation network. Such a network may not be designed to actually carry significant current, and thus may not be adequate to properly operate the stereo. I still wouldn't do it.

- Warren

 

[Averagesupernova]

If you connect the radio to a so-called proper ground, what is there that guarantees you that ALL of the ground current will go through it and not some of it going through the antenna shield? There is NO guarantee. I see it as not that much of a big deal. Most of the time an antenna connector has the shield connected right to the chassis of the radio. Running it through some kind of component is asking for a potential disaster. The reason is because when you have 2 wires running to different parts of the vehicle and both connecting to ground there is a chance (larger than you may realize) that a poor ground elsewhere on the vehicle can cause current to run into the antenna connector and out through the radios main ground. Not too likely any problem will develop when the antenna coax shield is connected right to the chassis during this type of failure but if it were connected to some sort of component, the current would most likely fry that component.

 

[chroot]

Averagesupernova,

What do you mean by "component?" Your argument is precisely the reason the two grounds would be isolated with an inductor or other network. The two grounds may in fact be somewhat different. While you want the two grounds to remain at nearly the same potential, you want your current to flow through only one.

- Warren

 

[megashawn]

it all comes down to misunderstanding, or misexplaining. My apoligies in that regard.

When I was reffering to antenna, I was talking about the entire component, not the individual wire inside that is the actual antenna. As to noise, while my expieriance with it begs to differ, it is entirely irrellevant to my original point, which I have long forgotten by now.

I will try to be more technical in the future