Properly grounding a motherboard - in a test environment...

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Postby robprime » Wed Dec 15, 2004 9:38 am

On the other hand, I agree with gutt3d. I had every component to my system laid out on cardboard, mobo, drives, p/s, fans, all of it and it ran just fine.
And, just a concept here, but wouldn't a p/s be designed to ground however much power it was designed to put out? Really, I don't think it can do anything but that, can it?
Because due to all my recent problems I had thought to isolate the whole damn system. It really wouldn't be that hard to do, and I was wondering why they weren't designed like that to start with.
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Postby colinJohn » Wed Dec 15, 2004 9:42 am

so are you going to cut the black cable to prove it ;-)
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Postby robprime » Wed Dec 15, 2004 10:12 am

Okay, here's another thought. In most electrical equiptment the chassis ground is present as a safety device, in case a component inside the case shorts or arcs to the case. The ground wire is supposed to conduct that current to ground instead of the next person who touches the case acting as the conductor, getting the bejesus shocked out of them, in other words. And actually, just thinking about that, it seems rather unsafe to be grounding system power through the case which is regularly handled by people.
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Postby robprime » Wed Dec 15, 2004 10:26 am

I mean some of these power supplies are rated at serious amperage, +12V@18 amps, that sort of thing. Way more than enough to kill. Yet if system power grounding is not the function of these holes then why are so many problems caused by poor ground, and why did these power supplies fail due to poor grounding, assuming that was really the problem?
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Postby beaconengr » Wed Dec 15, 2004 11:37 am

Well, i was clearly correct with one of my assertions...this is a controversial issue..however, answering a portion of the previous post, i doubt that any power supplies are failing due to poor grounding...i have used far too many power supples in older buildings that dont even have grounds..no issues
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Postby kokalo » Wed Dec 15, 2004 1:06 pm

There are two different types of ground you guys are referring to in this discussion:
* Circuit ground (GND) or the connection to the negative terminal of the PSU/battery, necesary for the operation of the DC electrical circuit it completes.
* Electrical/mains ground of the AC circuit feeding the power supply, also referred to as EARTH, designed for safety.

Since the GND is electrically isolated from the Neutral lead of the mains supply to the PSU by the transformer that also steps down from 110/115/220/230/240V to 12/5/3.3, it would be wrong and dangerous to connect it to Earth

Metal Case is (since it is metal, and fault in the PSU could make it electrified with respect to Earth) is Earthed via the Green/Green&Yellow lead in the mains cable. Thus any fault condition on the AC side of the PSU electrifying the case would create a short-circuit (actually an "extremely low resistance path") to Earth, and trip the circuit-breaker, potentially saving users from harm/death by electrocution.

Just my 2 cents worth! :D
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Postby video » Wed Dec 15, 2004 3:02 pm

Not only if you do not understand how to do an install (build or trouble shoot) correctly, or the basics in electronics, I'll throw something else in the mix here for ya. I do happen to know about it, but I will send you in a direction that I have "NEVER" heard anyone seem to realize on here that will and could be your problem for pws problems, computer bugs, systems that are just never right "at" the place they are in use, but when you bring them back for service they seen to be fine. Not every house has the right wiring in it, has been wired correctly.
An over sight made more often the one realizes.



Reversed Polarity

An electrical receptacle outlet with a reversed polarity condition is an outlet with an improper wiring condition and such conditions may be hazardous and repair is required.


I found something that may be of interest to you, to learn more.

http://www.inspectamerica.com/Home_Inspection_Library/Home_Inspection_Encyclopedia/Electrical_Encyclopedia/electrical_encyclopedia.html
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Postby robprime » Wed Dec 15, 2004 6:46 pm

My point is that I'm sure that none of the main system power will be routed through these motherboard ground points. whatever their absolute voltage potential may be. The idea that someone would design a system that used the case as a conductive path for any significant current is idiotic, and probably criminal, literally.
So I can only think that they are used in some secondary manner, perhaps as a safety path in case of certain motherboard shorts, perhaps as a path to shunt overvoltages of mobo components, perhaps as a path to sink stray inductances through. I'd really like to know.
This would explain why a system will seem to work fine out of the case but may be experiencing reduced efficiency, reliability, and safety.
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Postby tedybear » Wed Dec 15, 2004 9:17 pm

Ok Campers...I'm gonna really screw with peoples minds on this one.

I've got sitting in front of myself...a spare motherboard used for one of the games at work: DFI CA64-TC

This board makes full use of the motherboard stand-off's as a SECONDARY ground path. Yes Campers...ya read it correctly. Here's the dealey. On the side of the board near the rear edge? All the sheilding for the ports are soldered to the board, and that trace goes right to the silver ringed mounting holes. Same with the audio ports and usb ports. This is going to of course be different for each manufactor. But it's used from the looks of it, as a secondary ground path for FIELD GROUND/CHASSIS GROUND!

So in case you happen to get a static discharge while plugging in a USB connector....printer..keyboard.. It's made to use that grounding path, right to earth ground so you do not fry componets. It also provides an additional "earth ground" to the IDE and floppy connectors as well. Consider it a 'redundent' ground path if you want to. Some of the holes surrounded by silver are not connected by a 'trace' which is visiable, but keep in mind that boards are made of several layers..and the connection may be internal so we can't see it.

So it's a redundent earth ground. Glad I stored that motherboard here so I could look at it and get some meter readings.

Now as to the ? about why it works fine and dandy on a bench test...and also in a case? As I've mentioned it's a redundent ground, probably for a "safety" in case another ground path fails.

Figured I would chime in on it, considering I had the spare motherboard to physically exam the connections.

Also each motherboard manufactor does things their own way, so what's true in this DFI board might not apply fully to a board made by a different maker.

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Postby Copper » Thu Dec 16, 2004 12:18 am

kokalo wrote:There are two different types of ground you guys are referring to in this discussion:
* Circuit ground (GND) or the connection to the negative terminal of the PSU/battery, necesary for the operation of the DC electrical circuit it completes.
* Electrical/mains ground of the AC circuit feeding the power supply, also referred to as EARTH, designed for safety.

Since the GND is electrically isolated from the Neutral lead of the mains supply to the PSU by the transformer that also steps down from 110/115/220/230/240V to 12/5/3.3, it would be wrong and dangerous to connect it to Earth




Being an electrical engeineer , in the Uk mains comming to your house , neutral and ground/earth are connected together. This is to emsure you have an electrical safty ground / earth at all times
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