Why do computers have ground cables when the entire case is ground?

[LloydLynx]

So with a vehicle, positive wires go to each component and the body is used as ground. That means there are no ground cables between the component and the battery. Why aren't computers like this. 

 

I came to this realization a while ago while fitting a case fan into an Optiplex using a chopped SATA extention cable. I tested my idea by connecting the negative of the fan to the case and it worked like normal. I tested continuity across as many points in the case I could think of and every surface that you'd think would have ground did in fact have ground, including the ground prong on the mains AC plug. 

 

I can't image using the case as ground would have any more resistance or interferance than using ground wires along side the positive wires, I'd think it'd be even better. Having ground wires also takes up more space and makes cables less flexible. 

 

I can't think of a single reason ground wires could provide any advantage over case ground. Why are computers setup like this?

[CommanderAlex]

18 minutes ago, LloydLynx said:

So with a vehicle, positive wires go to each component and the body is used as ground. That means there are no ground cables between the component and the battery. Why aren't computers like this. 

 

Cars use the frame as a ground as the ground is connected back to the battery to complete the circuit. 

 

Keep in mind that ground on an electrical outlet is connected back to the neutral side in a circuit breaker box (normally). 

[OhioYJ]

It's simpler (to have ground wires in this case that is)? Look how many cases now are powder coated, or for that matter made of a material that does not conduct that well. Not to mention the current consumption is quite high in some cases, a bad connection could result in arcing / sparking, heat, just in general bad things, not to mention increased resistance across everything else down stream.

 

Even in a vehicles for something that needs a clean connection will get a dedicated or isolated ground wire run. Otherwise you will get noise. Having your blower motor creating whining noise in a CB radio or just a regular radio for that matter is very annoying.

[Imbadatnames]

12 hours ago, LloydLynx said:

So with a vehicle, positive wires go to each component and the body is used as ground. That means there are no ground cables between the component and the battery. Why aren't computers like this. 

 

I came to this realization a while ago while fitting a case fan into an Optiplex using a chopped SATA extention cable. I tested my idea by connecting the negative of the fan to the case and it worked like normal. I tested continuity across as many points in the case I could think of and every surface that you'd think would have ground did in fact have ground, including the ground prong on the mains AC plug. 

 

I can't image using the case as ground would have any more resistance or interferance than using ground wires along side the positive wires, I'd think it'd be even better. Having ground wires also takes up more space and makes cables less flexible. 

 

I can't think of a single reason ground wires could provide any advantage over case ground. Why are computers setup like this?

Ease of use etc. you’d have to use new wires every case to get a good earth. Rather than shipping your 30x SKUs with the same cables 

[Rocketdog2112]

With all the computers on cars nowadays, multiple ground points are used throughout the vehicle. Even the hood and fenders have grounding wires attached to them to ensure a complete ground loop.

 

Case in point....

The wife's 2005 Toyota 4Runner began to experience dash light issues. Not only the gauge illumination, but check engine and other warning lights. A classic grounding issue.

The culprit ended up being a corroded ground wire that connected to the inside of the drivers side fender, Looking under the hood, there's probably 12 or more smaller ground wires attached everywhere.

Depending on a single frame or engine ground nowadays is apparently not acceptable.

Adding extra ground wires to components also helps shorten and isolate the path to a proper ground without exposing other electronics to power faults.

[Mark Kaine]

21 hours ago, LloydLynx said:

So with a vehicle, positive wires go to each component and the body is used as ground.

#Dont laugh at me, but how does that work if a car has rubber tires? 

 

 

btw, if it is like i think, thats your answer why it is like that in pcs, and cars are a "special case" not really "grounded" at all because they only have 12v instead of 120 or 240v (which is a lot more deadlier)

 

21 hours ago, CommanderAlex said:

Cars use the frame as a ground as the ground is connected back to the battery to complete the circuit. 

i get the feeling there are two different "grounds" in electronics...  

 

 

basically a car electronics are a "closed loop" whereas a pc isnt, a pcs "ground" is connected to the earth (quite literally) through the ground wire in the outlet?

 

 

[CommanderAlex]

7 minutes ago, Mark Kaine said:

i get the feeling there are two different "grounds" in electronics...  

Well, yes. I was just thinking more on the "macro" or bigger level then in between smaller circuits. 

[Mark Kaine]

7 minutes ago, CommanderAlex said:

Well, yes. I was just thinking more on the "macro" or bigger level then in between smaller circuits. 

i see, it was a serious question though,  i really only know the basics of how electrical circuits work (which btw seems way more complicated than it initially seems)

 So why are things grounded at all, afaik an outlet for example doesn't need a ground to function?  its just better for security reasons if it has. and do really all pc cases have a ground? Ive seen it in mine and it strongly reminds me of old record players which also have a "ground wire" which they certainly don't need, you'll just get terrible interference/ noise if you don't use it... 

 

[CommanderAlex]

4 minutes ago, Mark Kaine said:

So why are things grounded at all, afaik an outlet for example doesn't need a ground to function?

As far as I understand, outlet's are grounded to prevent electrical shocks and/or harm humans. The ground acts as an extra safety feature to prevent any harm (in terms of an electrical outlet with AC voltage. Now, I'm not too sure how it would work with DC voltage). 

[stipuledfatcat]

2 minutes ago, Mark Kaine said:

i see, it was a serious question though,  i really only know the basics of how electrical circuits work (which btw seems way more complicated than it initially seems)

 So why are things grounded at all, afaik an outlet for example doesn't need a ground to function?  its just better for security reasons if it has. and do really all pc cases have a ground? Ive seen it in mine and it strongly reminds me of old record players which also have a "ground wire" which they certainly don't need, you'll just get terrible interference/ noise if you don't use it... 

 

Spoiler

So first ground does not always equal common. Ground refers to using the earth as a giant current sink, common is the common reference point for voltages for a given circuit and as a return path for the current. You can use the ground as a common but not the other way around. There are many reasons for using proper grounding with a big one being safety. Ideally all electronics would be housed inside a metal enclosure with the enclosure connected to ground, that way if a wire comes loose or a spark inside the enclosure occurs it wont zap you if you touch the box. Of course the other option is to house it in a non conductive enclosure but then you also loose the ability to trip a breaker if something happens. The other benefit of using ground as your common is that it is literally the ground, or earth depending on where you grew up, and it acts a a very stable voltage reference point which is hard for EMI noise to overpower.

 

Now for PC cases, unless you have a physical ground wire (I think the code in Canada is a yellow wire with a green stripe) attached to it you should assume its not grounded. The PSU on the other hand should be grounded especially since it is connected to a high ish AC voltage and if it has a good bare metal to metal contact with the PC case then it would be grounded as well. But again for safety assume it's not, even if function wise it is.

 

You also have to bear in mind that there are different ways of grounding which have their own nuances. The main one for safety is that if your ground path is long enough, through daisy chaining grounds, or large impedance in the path, you can end up with a non zero voltage at a point you think is ground. Which for safety is dangerous because now if some one touches that point and ground they become a current path and get a nice little, or not so nice big, shock.

 

Anyways coming back to PC cases and their use of the case itself as ground. Most likely the reason is it's cleaner and less prone to user error to just use a connector for "grounding" (really its the common but both are the same in this situation). It also provides a more reliable connection so you don't end up with sparks and fire like that one case manufacturer featured on Gamers Nexus.

 

 

 

Pardon the ramblings on grounds, it's a fairly broad subject so I might have gone off into some areas that don't specifically relate to the question at hand.

[Mark Kaine]

29 minutes ago, CommanderAlex said:

As far as I understand, outlet's are grounded to prevent electrical shocks and/or harm humans. The ground acts as an extra safety feature to prevent any harm (in terms of an electrical outlet with AC voltage. Now, I'm not too sure how it would work with DC voltage). 

That's about how i understand it too.

So my answer to OPs question is the PC needs a ground wire, because, just like a car, the pcs case is not the "ground" ie earth,  it needs to be connected to a ground wire, which is connected to the outlets earth (aka ground) ultimately through the psu, for security reasons.  there might also be also noise / interference reasons as mentioned above but im not sure about that and i think the primary function is for security. 

 

Could be wrong,  is my understanding though...

 

 

8 minutes ago, stipuledfatcat said:

So first ground does not always equal common.

Ah, I figured this was a language thing perhaps...

 

So, there are actually two grounds ?

 

1 is in the psu basically ...

 

and the other is needed for what?

 

i think you explained it well, but that point is still unclear (I think its all somehow related to a feedback loop kinda thing and my "answer" possibly wasn't entirely incorrect? )

 

 

[stipuledfatcat]

21 minutes ago, CommanderAlex said:

As far as I understand, outlet's are grounded to prevent electrical shocks and/or harm humans. The ground acts as an extra safety feature to prevent any harm (in terms of an electrical outlet with AC voltage. Now, I'm not too sure how it would work with DC voltage). 

Some what the same way if the voltage is high enough, just have a random wire going into a ground plug and have some additional over current protection incase there's a short. Though for DC I only ever really saw it for noise reduction for cheap switching power supplies that have coupling problems. 

 

4 minutes ago, Mark Kaine said:

That's about how i understand it too.

So my answer to OPs question is the PC needs a ground wire, because, just like a car, the pcs case is not the "ground" ie earth,  it needs to be connected to a ground wire, which is connected to the outlets earth (aka ground) ultimately through the psu, for security reasons.  there might also be also noise / interference reasons as mentioned above but im not sure about that and i think the primary function is for security. 

 

Could be wrong,  is my understanding though...

 DC doesn't need a ground, the reference point is defined by either the battery negative or if there is some AC/DC conversion the common of that. This reference point can technically be any value, with respect to earth, and wont (but kinda will in some circumstances) change the function of the circuit as long as everything is referenced off of the same point. 

[LloydLynx]

@Commander @stipuledfatcat

Ok sorry to y'all for me thinking ground and common are the same thing. Every mention of ground in the original post should have been common. 

5 minutes ago, Mark Kaine said:

So my answer to OPs question is the PC needs a ground wire, because, just like a car, the pcs case is not the "ground" ie earth,  it needs to be connected to a ground wire, which is connected to the outlets earth (aka ground) ultimately through the psu, for security reasons.

You're completely correct. But due to me being dumb with words, it doesn't answer my original question. 

[Mark Kaine]

3 minutes ago, stipuledfatcat said:

DC doesn't need a ground, the reference point is defined by either the battery negative or if there is some AC/DC conversion the common of that.

Ah, i see... ok theres a difference,  but not sure you saw my edit,  i think we're really close to a proper answer,  hopefully.

 

13 minutes ago, Mark Kaine said:

Ah, I figured this was a language thing perhaps...

 

So, there are actually two grounds ?

 

1 is in the psu basically ...

 

and the other is needed for what?

 

i think you explained it well, but that point is still unclear (I think its all somehow related to a feedback loop kinda thing and my "answer" possibly wasn't entirely incorrect? )

 

 

[CommanderAlex]

1 minute ago, stipuledfatcat said:

Some what the same way if the voltage is high enough, just have a random wire going into a ground plug and have some additional over current protection incase there's a short. Though for DC I only ever really saw it for noise reduction for cheap switching power supplies that have coupling problems. 

Ah ok, just knowing that DC is different from AC, I didn't want to assume anything would be similar between the two. 

 

12 minutes ago, Mark Kaine said:

That's about how i understand it too.

So my answer to OPs question is the PC needs a ground wire, because, just like a car, the pcs case is not the "ground" ie earth,  it needs to be connected to a ground wire, which is connected to the outlets earth (aka ground) ultimately through the psu, for security reasons.  there might also be also noise / interference reasons as mentioned above but im not sure about that and i think the primary function is for security. 

 

Could be wrong,  is my understanding though...

I believe you're confusing with what the OP is asking. I'm pretty sure the OP is asking why not have the ground in computers, in terms of their components, be just the ground of the case instead of using a ground wire going to/from the PSU to a graphics card i.e. 

[LloydLynx]

22 hours ago, OhioYJ said:

Look how many cases now are powder coated, or for that matter made of a material that does not conduct that well. Not to mention the current consumption is quite high in some cases, a bad connection could result in arcing / sparking, heat, just in general bad things, not to mention increased resistance across everything else down stream.

That makes a lot of sense. That's probably why. But I question if resistance would also be the reason since the metal has so much area. 

[Mark Kaine]

2 minutes ago, LloydLynx said:

@Commander @stipuledfatcat

Ok sorry to y'all for me thinking ground and common are the same thing. Every mention of ground in the original post should have been common. 

You're completely correct. But due to me being dumb with words, it doesn't answer my original question. 

Nah, its cool, its also a language barrier thing obviously,  we just call things slightly different in Europe it would seem... which makes it even more difficult  

 

 

(i still think we'll figure this out soon :p)

 

 

 

 

 

[stipuledfatcat]

14 minutes ago, Mark Kaine said:

Ah, I figured this was a language thing perhaps...

 

So, there are actually two grounds ?

 

1 is in the psu basically ...

 

and the other is needed for what?

Earth and ground are the same, at least in Canada, and if you want to be super specific, though some engineers will use earth as one thing and ground and common as the same thing (but have it mean earth=ground, ground=/= common, except sometimes when it does, ain't engineering fun  ) .

Only ever 1 ground, and that is the big rock flying through space at crazy speeds. The other "ground" will just be some voltage reference point, and it could be floating with respect to ground or not if its connected.

All the DC voltages will be referenced off of that second "ground" and will be the currents return path. Anything that cares about voltage levels will also have to reference off of the same common. Think USB for example, its a 5V signal but if you run just the signal wire between two things that don't share a ground or common then it won't work.

 

2 minutes ago, LloydLynx said:

Ok sorry to y'all for me thinking ground and common are the same thing. Every mention of ground in the original post should have been common. 

Funny thing is even electrical engineers get lazy and just start calling everything ground and just thinking that anyone else is going to know what they mean. Can be a little bit dangerous when creating a circuit in the middle of the night and not paying full attention, linking a ground to a common and having sparks fly when you go to test it.

 

10 minutes ago, LloydLynx said:

That makes a lot of sense. That's probably why. But I question if resistance would also be the reason since the metal has so much area. 

Larger area would actually decrease resistance. That's why you will see circuits with large ground and voltage planes instead of individual traces going to each component. Unless you have a really long and skinny case then yea resistance would be high and you would end up with a non 0 voltage at one end.

[LloydLynx]

9 minutes ago, stipuledfatcat said:

Larger area would actually decrease resistance. That's why you will see circuits with large ground and voltage planes instead of individual traces going to each component. Unless you have a really long and skinny case then yea resistance would be high and you would end up with a non 0 voltage at one end.

I mean I'm wondering why that person thinks case metal would have resistance issues. I would think the case would be better than wires in that regard. 

[CommanderAlex]

1 minute ago, LloydLynx said:

I mean I'm wondering why that person thinks case metal would have resistance issues. I would think the case would be better than wires in that regard. 

I would also think electricity likes to take the path of least resistance to return to the source. With that being said, there are numerous pathways in a case that electricity could travel, but would be more resistive. A ground wire, on the other hand, provides the easiest way back as it's just a straight shot. 

[Moonzy]

1 minute ago, CommanderAlex said:

I would also think electricity likes to take the path of least resistance to return to the source.

electricity takes all available path to neutral
just that each path carries different weight depending on their resistance

say u have two resistor in parallel, one is 1 ohm the other is 100k ohm, electricity would flow through both to the otherside

[CommanderAlex]

3 minutes ago, Moonzy said:

electricity takes all available path to neutral
just that each path carries different weight depending on their resistance

say u have two resistor in parallel, one is 1 ohm the other is 100k ohm, electricity would flow through both to the otherside

Well, yes electricity will flow through both of those paths that you described, but the current (amount of electrical charge) in the 100,000 Ohm resistor will be lower than the 1 Ohm resistor. 

[Heliian]

You may not realize it but your mobo is probably grounded to the case through the mounting screws. 

 

2 wire DC circuits are more reliable whereas chassis grounds can cause problems because the materials are varying.  

 

Personally I like to refer to "earth" as a grounding point in the earth's surface and "ground" as a common grounding point.

 

Some vehicles have been made with positive grounds.  Polarity is another thing. 

 

 

 

 

[Lurking]

1 hour ago, Mark Kaine said:

#Dont laugh at me, but how does that work if a car has rubber tires? 

 

 

btw, if it is like i think, thats your answer why it is like that in pcs, and cars are a "special case" not really "grounded" at all because they only have 12v instead of 120 or 240v (which is a lot more deadlier)

 

i get the feeling there are two different "grounds" in electronics...  

 

 

basically a car electronics are a "closed loop" whereas a pc isnt, a pcs "ground" is connected to the earth (quite literally) through the ground wire in the outlet?

 

 

The car power source is DC and is the battery/alternator. So the electrons go from battery plus (red cap) via cables to the device, and back through the the frame to the negative of the battery. The only reason the frame is used is to save weight and money. They also could have ran separate wire. The ground (as in actual Street) isn't part of this circuit.

 

A PC has 2 "loops" the DC side (3.3 - 12V) works like in the car, except it goes from PSU and use 2 wires instead of using the chassis. I suppose one could use the case, but that may be made of plastic, or not closed, or the connections aren't great. And the case also is part of the AC ground (see below)

 

The AC side (from your outlet) is separated from the DC side by the PSU (for good reason since it is lethal). There is the line, and the neutral wire that run the current. It is AC, so it isn't +/-, but from a wiring point it works the same. The middle contact in your outlet is the ground and typically does NOT carry a current. This goes through the panelboard and the E-service to the actual ground. A building or service entrance typically has a ground rod or is bonded to steel in the structure. It isn't used for actual power and you could omit it and some old outlets don't have it. But don't omit it, it is a safety feature. That ground is connected to the metal case of the PSU, which is connected to the case. If the line voltage wire (120 or 230V!!!!!) would be damaged and touch the PSU case, your case would be lethal if you touch it! The ground will run the current to the ground (instead of through your body!). That will lead to high current and typically trip the breaker. So please don't use those outlets without ground, even if the PC "works" without. 

 

At the service entrance the neutral and ground actually bond together. But up to that point ground doesn't carry current (except when there is an issue). A common mistake is to install a sub-panel and bond neutral and ground in the sub panel as well. Don't do that!. Because in that case the grounds wire between the panels would carry a current under normal conditions. 

 

The tricky thing about electricity is, you can do things wrong and they appear to work. But you will have stray voltages and safety issues that are not immediately apparent. They become apparent when it is too late. So unless you really know what you are doing and are educated, never work on the high voltage side of a PC. Never open a PSU unless you plan to condemn it (or you actually are an expert).

 

[wseaton]

In regards to mounting screws this is not always the case. Ive actually tested this and found many MBs mounted in such a way, typically with with washers and standoffs that they are intermittently insulated from the case. This is a common problem with DIY and hence I'm convinced why they are prone to more MB issues than mass produced desktops and servers.

 

There's also the guy who won't touch RAM unless he's standing on an electrostatic matt or using a connected wrist ground. I applaud his caution, but all you have to do is touch the PC frame to ground yourself before touching RAM or other sensitive PC components.