Explain to me the concept of electrical ground

[Gautama2]

I've heard explanations from my teacher and online, but I've never understood it.

Why is it needed?

 

[Cogman]

What do you mean be electrical ground? Here is what Ill attempt.

Basically the ground state is a more fancy way of saying "as little charge as possible" Atoms don't like to have a charge put on them, so they do anything they can to get the charge off. Much like if you fill a tower with water and poke a hole in the bottom, water will come rushing out because it doesn't like the pressure around it.

if you are asking why it is needed from a safety standpoint, electricity will always take the easiest path (at least the majority of it will) A ground is often provided in electrical equipment so if something should fail or go wrong, the electricity travels through the ground wire and not the toddler.

 

[Gautama2]

Well, for example, if I'm hooping up an audio system I have a cable with 3 wires. One for the left channel, one for the right channel, and one for ground. Why do I need a ground here?

 

[Cogman]

Electricity has to flow, if it doesn't flow then you're circuit is useless. the ground provides the place for the electricity to flow, the circuitry regulates how fast it is able to flow. Often it is easy to just tie your 0's to ground when dealing with transistors and not have to worry about gate delay and such. But, the main reason is that if your electrical current is not flowing, then you really don't have a current

 

[SinxarKnights]

Edit: Cogman beat me to it.

In your example, the "ground" is just the return path for both speakers, a "common" if you will. This is required or electricity will not flow without the return path or a short to ground.

Also in your example, it may be like that to help out the end user keep the speakers in phase with each other. Most audio circuits [that I have seen] have the "ground" or "negative" or "common" internally connected for both channels, assuming its a two channel amp. Requiring the use of two, two conductor wires, making it possible to reverse one of the speakers (you know, red to black, and black to red - and the other hooked up normally) causing the speakers to be out of phase.

I have never seen a 3 conductor audio cable before.

So I guess its needed because current will not flow from a single conductor without some type of ground. This includes lightning, and your house wiring.

I might not be very clear about this subject, but I think its hard to explain without some form of drawing. Or maybe I just suck at trying to teach.

 

[Gautama2]

Originally posted by: SinxarKnights
I have never seen a 3 conductor audio cable before.

Really? How about a headphone cable, or a mini-mini interconnect cable?

 

[The Boston Dangler]

Originally posted by: Gautama2
Well, for example, if I'm hooping up an audio system I have a cable with 3 wires. One for the left channel, one for the right channel, and one for ground. Why do I need a ground here?

what kind of cable? RCA interconnects from a deck to an amp? note that each RCA is a coaxial connector, the inner is positive and the outer is negative. that's the entirety of the signal flow. if the cable is coax, the magnetic field of the outer conductor will increase signal flow and reject ingress (outside noise getting in). if the cable is twisted pair, signal will suffer higher attenuation and ingress. this is not an issue with the distances you're dealing with.

the ground cable (usually 18 AWG, maybe a little more) is there to provide ground continuity between all connected components. this is to prevent noise and damage to the equipment.

 

[Nathelion]

Originally posted by: Cogman
What do you mean be electrical ground? Here is what Ill attempt.

Basically the ground state is a more fancy way of saying "as little charge as possible" Atoms don't like to have a charge put on them, so they do anything they can to get the charge off. Much like if you fill a tower with water and poke a hole in the bottom, water will come rushing out because it doesn't like the pressure around it.

if you are asking why it is needed from a safety standpoint, electricity will always take the easiest path (at least the majority of it will) A ground is often provided in electrical equipment so if something should fail or go wrong, the electricity travels through the ground wire and not the toddler.

I feel compelled to point out that ground is not by any means "as little charge as possible". Ground means "zero electric potential". In a strong electric field, for example, this may require quite a bit of charge.
In everyday situations though, a grounded object will generally end up electrically neutral.

 

[SinxarKnights]

Originally posted by: Gautama2

Originally posted by: SinxarKnights
I have never seen a 3 conductor audio cable before.

Really? How about a headphone cable, or a mini-mini interconnect cable?

Good, point. I never even thought of that. That brings back bad memories of trying to repair one of those headphone cables that has the clear coating on the wire instead of plastic or rubber.

 

[Born2bwire]

Originally posted by: SinxarKnights

Originally posted by: Gautama2

Originally posted by: SinxarKnights
I have never seen a 3 conductor audio cable before.

Really? How about a headphone cable, or a mini-mini interconnect cable?

Good, point. I never even thought of that. That brings back bad memories of trying to repair one of those headphone cables that has the clear coating on the wire instead of plastic or rubber.

I think in this case these may be biwires or a differential input. That is, a single channel has three wires, +,GND,-. The + and - are just 180 degrees out of phase to each other. The signal is reproduce by taking the difference between the + and -. One of the advantages is that this removes any common noise between the two signals.

(I am churning this out really quick so I may be confusing this with the more common use of differential signals in microwave circuits but I think it's the same thing when you are biamping a speaker, or have a differential input).

 

[PottedMeat]

A stereo headphone plug has 3 connectors - left channel, right channel, and the ground return.

(I am churning this out really quick so I may be confusing this with the more common use of differential signals in microwave circuits but I think it's the same thing when you are biamping a speaker, or have a differential input).

I think you're thinking of a bridge tied load - a signal feeding two amplifiers ( one non inverted, the other inverted ) then the outputs are fed into the load - doubling the possible voltage swing ( referenced to the ground back at the amplfiers ).

Or maybe those XLR differential connectors they use for microphones maybe?

 

[Born2bwire]

Originally posted by: PottedMeat
A stereo headphone plug has 3 connectors - left channel, right channel, and the ground return.

(I am churning this out really quick so I may be confusing this with the more common use of differential signals in microwave circuits but I think it's the same thing when you are biamping a speaker, or have a differential input).

I think you're thinking of a bridge tied load - a signal feeding two amplifiers ( one non inverted, the other inverted ) then the outputs are fed into the load - doubling the possible voltage swing ( referenced to the ground back at the amplfiers ).

Or maybe those XLR differential connectors they use for microphones maybe?

Yeah, now I thought of the name, balanced outputs, which can be done using XLR connectors. Some headphones can be wired and amped as balanced outputs and I speakers can be done this way too (though I haven't heard of it being used with anything other than a XLR connector). Biwiring/biamping is a different thing, with four connections, not three.

 

[Leros]

Ground has zero potential, ie 0 volts.

 

[bobsmith1492]

Originally posted by: Leros
Ground has zero potential, ie 0 volts.

With respect to... ?

Often "Ground" was literally connected to the dirt beneath your feet, so it is also called "Earth." This was and is for safety reasons for household appliances - metal shells around them are connected to the earth so there is no chance of a potential developing between, say, your light switch and a puddle on the carpet.

In Britain and Australia, I think, "earthed" is used instead of "grounded." Earth ground is often used here in the US to mean safety ground, i.e. connected to the ground beneath your feet.

What does electrical ground mean?
1. Zero potential, or the reference point for measuring or defining voltages within a circuit
2. Safety (earth) ground, that is, the dirt under one's feet, used in industrial/commercial/residential wiring

 

[wwswimming]

a near infinite source of electrons, with zero potential energy.

electrical circuits are a little like aikido, they usually need a good ground.

but that may not explain it.

ground is (usually) the horizontal line at the bottom of the page.

ground is ... what you have to grab if you want to test a toy design for
safety by putting the active line on your tongue. i did that once with
48 volts.

ground is what you let go of when you realize you've gone too far
testing a toy design for safety.

 

[Rubycon]

In theory ground should be at zero volts but never is. The resistance of your ground and bonding wires should be kept to a minimum to reduce ground offset. In unbalanced audio systems this is crucial to eliminate noise (difficult) and at longer runs the use of a balanced system is always required.

 

[Paperdoc]

Your question highlights one of the reasons for confusion. Ground is at ZERO volts (electrical potential) with respect to - what? - the GROUND! In most electrical systems some part of the device or system is connected in some way to the earth outside. For example, in most homes at the breaker panel there is a separate wire (often bare copper) connected to a Ground Terminal in the box, and out to a solid connection to the metal water supply pipe entering the house. This depends on the idea that the buried water pipe, many feet long in the earth, has a good enough connection to the earth that it really does have the same electrical potential - that is, it is ZERO volts different from the real earth. Moreover, that connection is good enough that any small current trying to flow through the wire to the earth can do so with very little resistance, so the wire can stay at zero volts even when it is carrying a modest current to the real Ground.

In modern house systems, all the cables from the panel out to outlets in the house have at least three wires: one is called "Hot", and is the power "supply"; one is called "Neutral", and it is the path for current return; the third (usually bare) is called "Ground", and its only function is to be prepared to carry current directly back to the Ground terminal in the box (and hence to the real earth) in an unusual situation. For all normal situations, there should be absolutely no current on the Ground wire. With no current flowing through it, its potential really is a zero volts with respect to true earth Ground.

Now, the truth is that the "Hot" and "Neutral" lines really are just two ends of the transformer winding on the unit supplying your house (or, more precisely, one end and a center tap, but that's another detail to confuse you). By convention, however, in the USA, Canada and many countries, household wiring systems actually connect the power supply transformer's center tap line to real earth ground, both at the transformer on the pole and in your house breaker panel. That establishes a relationship, or a reference point, such that the "Neutral" lines all through the house should be close to zero volts with respect to the earth at all times. However, the Neutral lines DO carry significant currents (they are the electrical return path for the current supplied buy the Hot line); that means, because they have a small but non-zero resistance, that a Neutral line may actually have a non-zero voltage on it in many places. So it is different from a true Ground line.

Now back to consumer devices - for example, an audio amplifier with outputs to speakers. For each speaker there MUST be two wires so that current can be sent out to the speaker, through it, and back on the other wire to the amplifier. That is a circuit, and you must have both wires for a complete circuit that will carry a current around it and through the device (speaker) that is doing the work. It happens, since the voltages in such a circuit are small, that many manufacturers design their amplifiers so that, at the output of the speaker circuit, one of those two wires actually is connected to the metal chassis of the amplifier, which also is connected (via the ground (often green-covered) wire in the unit's power supply cord) to Ground in the electrical system of your house. So we've all got into the habit of calling one of the two speaker wires a "Ground" wire, and the other the "Signal" wire. In some speaker cables the cord actually contains two "Signal" wires (one for each of two speakers) but, instead of two separate "Ground" wires for the two return paths they use only one, because they both end up going to the same place at the amplifier end.

In professional systems like broadcast studios and high-end consumer systems this design, with one side of a circuit connected to true Ground, is not used. Instead, in each circuit there are two wires (call them + and -) to complete the circuit, and both are isolated from true Ground. Then a real Ground lead also is used, often as a noise shield to protect the other two electrically. These "balanced" circuits with differential amplifiers have superior characteristics for noise reduction, etc. and that's why they are used in the best systems, but not in most consumer-level systems.