Grounding the motherboard.

[Wedge]

I'm sure this is answered in google somewhere, but I'm going to ask
again.
I have a nephew that is building a computer and has a plastic/acrylic
case. He has already gone through two Motherboards and was told that
he needed to ground the PS to the Motherboard. If this is true, does
he need to ground "all" the stand offs or just certain ones. If just
certain ones need to be grounded, how would one know which ones
should be tied to the PS.

V/R
Greg Wejrowski

 

[jpsga]

I'm sure this is answered in google somewhere, but I'm going to ask
again.
I have a nephew that is building a computer and has a plastic/acrylic
case. He has already gone through two Motherboards and was told that
he needed to ground the PS to the Motherboard. If this is true, does
he need to ground "all" the stand offs or just certain ones. If just
certain ones need to be grounded, how would one know which ones
should be tied to the PS.

V/R
Greg Wejrowski

Greg, I wonder what they mean, as the PS ground is connected to the MB
through the 20 pin socket.
Maybe they want the PS case wired to the MB.
JPS

 

[David Maynard]

I'm sure this is answered in google somewhere, but I'm going to ask
again.
I have a nephew that is building a computer and has a plastic/acrylic
case. He has already gone through two Motherboards

What does "gone though two motherboards" mean? They failed for some reason?

When you say plastic/acrylic case, do you mean the whole thing is plastic,
or just a window? Or a metal frame inside with the outside acrylic?

and was told that
he needed to ground the PS to the Motherboard. If this is true, does
he need to ground "all" the stand offs or just certain ones. If just
certain ones need to be grounded, how would one know which ones
should be tied to the PS.

Well, there are two main reasons for the motherboard grounds: ESD (static
discharge) protection and EMI (noise) reduction.

For minimal ESD protection you'd want to ground the two motherboard
mounting screws on either side of the rear I/O area (the place where
outside ESD could enter). PCI end plates should also be grounded. All of
those should go back to the 'chassis' ground at the PSU. (Is there any
metal in the thing?)

EMI is problematic since, with an acrylic case, you've pretty much
abandoned EMI containment when it comes to TV/Radio interference, or
anything else electronic nearby.

The other layer of EMI containment is to prevent things inside the computer
from interfering with itself (which reduces outside interference too, of
course). To that end the remainder of the motherboard mounting holes are
normally grounded to the metal back plate it's mounted on which, in turn,
is chassis grounded. Frankly, I'd suggest you use a metal back plate since;
who cares what the rear of the motherboard looks like? Then ground the back
plate to the PSU. That takes care of the ESD connection mentioned above and
provides some EMI protection. If the mounting plate is 'isolated', meaning
no chassis metal there to mount it to, the chassis connection to the PSU
should be from the corner nearest the rear I/O area so ESD discharge goes
directly (not across the plate) to the PSU chassis ground (PSU is
internally earthed).

I.E.

Chassis Ground
/--------------\
------------------------ ---------
| | I/O area | | PSU |
| | | | |
| ----------| ---------\
| | --- plug earth
| Motherboard |
------------------------

I'd use braided copper ground strap.
For examples: http://www.amgndsys.com/

The floppy, CD, and hard drive(s) should also be chassis grounded.

 

[bill bixby]

yes i have always been told to make sure to ensure a good ground on drives
but figured that the steel drive cage would do nicely
i would use thin copper between the mount holes and drives kinda hiding it
also could do this under the MoBo using brass stand offs since you cant see
through the mobo shouldn't interfere with the visuals
you will have to adhere it some how and keep it tight to the acrilic/plexi
good luck

What does "gone though two motherboards" mean? They failed for some
reason?

When you say plastic/acrylic case, do you mean the whole thing is
plastic, or just a window? Or a metal frame inside with the outside
acrylic?


Well, there are two main reasons for the motherboard grounds: ESD
(static discharge) protection and EMI (noise) reduction.

For minimal ESD protection you'd want to ground the two motherboard
mounting screws on either side of the rear I/O area (the place where
outside ESD could enter). PCI end plates should also be grounded. All of
those should go back to the 'chassis' ground at the PSU. (Is there any
metal in the thing?)

EMI is problematic since, with an acrylic case, you've pretty much
abandoned EMI containment when it comes to TV/Radio interference, or
anything else electronic nearby.

The other layer of EMI containment is to prevent things inside the
computer from interfering with itself (which reduces outside
interference too, of course). To that end the remainder of the
motherboard mounting holes are normally grounded to the metal back plate
it's mounted on which, in turn, is chassis grounded. Frankly, I'd
suggest you use a metal back plate since; who cares what the rear of the
motherboard looks like? Then ground the back plate to the PSU. That
takes care of the ESD connection mentioned above and provides some EMI
protection. If the mounting plate is 'isolated', meaning no chassis
metal there to mount it to, the chassis connection to the PSU should be
from the corner nearest the rear I/O area so ESD discharge goes directly
(not across the plate) to the PSU chassis ground (PSU is internally
earthed).

I.E.

Chassis Ground
/--------------\
------------------------ ---------
| | I/O area | | PSU |
| | | | |
| ----------| ---------\
| | --- plug earth
| Motherboard |
------------------------

I'd use braided copper ground strap.
For examples: http://www.amgndsys.com/

The floppy, CD, and hard drive(s) should also be chassis grounded.

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[Wedge]

What does "gone though two motherboards" mean? They failed for some reason?

When you say plastic/acrylic case, do you mean the whole thing is plastic,
or just a window? Or a metal frame inside with the outside acrylic?


Well, there are two main reasons for the motherboard grounds: ESD (static
discharge) protection and EMI (noise) reduction.

For minimal ESD protection you'd want to ground the two motherboard
mounting screws on either side of the rear I/O area (the place where
outside ESD could enter). PCI end plates should also be grounded. All of
those should go back to the 'chassis' ground at the PSU. (Is there any
metal in the thing?)

EMI is problematic since, with an acrylic case, you've pretty much
abandoned EMI containment when it comes to TV/Radio interference, or
anything else electronic nearby.

The other layer of EMI containment is to prevent things inside the computer
from interfering with itself (which reduces outside interference too, of
course). To that end the remainder of the motherboard mounting holes are
normally grounded to the metal back plate it's mounted on which, in turn,
is chassis grounded. Frankly, I'd suggest you use a metal back plate since;
who cares what the rear of the motherboard looks like? Then ground the back
plate to the PSU. That takes care of the ESD connection mentioned above and
provides some EMI protection. If the mounting plate is 'isolated', meaning
no chassis metal there to mount it to, the chassis connection to the PSU
should be from the corner nearest the rear I/O area so ESD discharge goes
directly (not across the plate) to the PSU chassis ground (PSU is
internally earthed).

I.E.

Chassis Ground
/--------------\
------------------------ ---------
| | I/O area | | PSU |
| | | | |
| ----------| ---------\
| | --- plug earth
| Motherboard |
------------------------

I'd use braided copper ground strap.
For examples: http://www.amgndsys.com/

The floppy, CD, and hard drive(s) should also be chassis grounded.

There is NO METAL at all in the case. Its all acrylic.
When I said he went through two mother boards I ment he has either
broke two or had two defective ones sent from the factory.. Either way
he is on the his third motherboard.
He didn't keep the manual that came with the case. (claims one wasn't
in the box), but I would think that the case manufacture would include
a note about grounding the computer parts and maybe (hey you can wish)
they would even include some grounding straps/cables.

Here is what we did so far and I will see him again at Christmas to
help pretty things up. We took aluminum wire and tied all the brass
standoffs together then ground 4 of these standoffs to the PS chassis.
I thought about taking some measurements and then making a grounding
harness out of braided copper and some washers, or checking prices
from the website provided above.

I forgot about grounding the drives and such.. I'm thinking he'd be
better off just getting new METAL case. He just started going to LAN
parties and wanted a plactic case to save on weight. I'm thinking the
extra 5 or 10 pounds will do him some good.

V/R
Greg Wejrowski

 

[nobody]

He just started going to LAN parties and wanted a plactic
case to save on weight.

Yeah, I'm sure that's the real reason.

Has he factored in the added weight of the cold cathode lights,
fan LEDs and the water cooling rig with the UV-reactive tubing?

 

[w_tom]

The primary purpose of grounding is human safety. Chassis
are often metal to avoid EMC problems. Metal creates a
complication; exposed metal must then connectio to safety
ground in circuit breaker box. How we make that connection is
defined by other problems that can be created when connecting
safety ground to metal chassis.

Black wires from power supply are logic ground for
motherboard and peripherals. Notice an adjective before each
ground. All grounds are unique. And all grounds connect back
to the breaker box - for human safety. How we interconnect
those grounds can cause or avoid other problems.

As described, there is no reason for the missing chassis
ground to cause hardware failure. Such comments are more
typically from one who sees something different - and assumes
that is sufficient to blame the something different. Some
people have little comprehension of ground. For example, many
fail to understand the number one reason why we inteconnect
the different grounds - human safety.

Every ground connection required by motherboard and
peripherals - a logic ground or DC ground - is provided by
multiple black wires in power connectors. If these become
disconnected or missing when computer is powered (computer is
powered anytime the power cord connects to wall receptacle
even when it appears off), then damage can result; especially
to peripherals that use multiple voltages (+5 and +12 - the
red and yellow wires). Acrylic chassis may have created
static electicity that could damage hardware. But no chassis
ground does not cause hardware failure.

 

[John Doe]

I'm sure this is answered in google somewhere, but I'm going to ask
again.
I have a nephew that is building a computer and has a plastic/acrylic
case. He has already gone through two Motherboards

Why not get an ordinary metal case.

Good luck.




and was told that

 

[David Maynard]

There is NO METAL at all in the case. Its all acrylic.

Yes. That's what I figured, but ya never know

When I said he went through two mother boards I ment he has either
broke two or had two defective ones sent from the factory.. Either way
he is on the his third motherboard.

I suggest there's something else wrong other than just the case as it
should run, regardless. The 'metal' is not needed for the basic electrical
operation and, in fact, one of the 'debug' tools when one has a problematic
motherboard is to remove it from the case (people sometimes get the
standoffs in the wrong place and that causes the motherboard to not
function if it contacts one where it's not supposed to).

Has be built a computer before?

He didn't keep the manual that came with the case. (claims one wasn't
in the box), but I would think that the case manufacture would include
a note about grounding the computer parts and maybe (hey you can wish)
they would even include some grounding straps/cables.

One would think so but most cases come with no instructions. The builder is
expected to already have the requisite knowledge and skills. Well, that's
probably what they would say. A cynic must say it's because they're cheap
and unprofessional.

Here is what we did so far and I will see him again at Christmas to
help pretty things up. We took aluminum wire and tied all the brass
standoffs together then ground 4 of these standoffs to the PS chassis.
I thought about taking some measurements and then making a grounding
harness out of braided copper and some washers, or checking prices
from the website provided above.

Running individual wires is not the same as a metal backplate and won't
provide the EMI reduction as, for EMI, it isn't simply a matter of
'connecting' them; the metal plate is 'what does it'.

If you're not going to use a metal plate then run a ground strap from the
two I/O area standoffs, as I mentioned, to the PSU and leave the others
unconnected.

But we're not talking work vs non working here. The ESD protection is
simply for that and if there is no ESD discharge to protect from then it
doesn't matter. EMI protection is to reduce interference with other
devices. Internal interference often takes the form of noise in the audio
from display and/or disk activity and external is, of course, noise in TVs,
radios, and cordless telephones.

Radiated EMI in the reverse direction, from external sources, can cause
erratic PC behavior but you don't usually see that in a normal home
environment.

I forgot about grounding the drives and such.. I'm thinking he'd be
better off just getting new METAL case. He just started going to LAN
parties and wanted a plactic case to save on weight.

Fascinating. I understand the weight consideration but had never thought of
an acrylic case for that purpose and I'm not sure it helps all that much,
especially after all the components are installed, but none of the acrylics
I see provide a weight spec to go by so I can't really say.

But, for example, I built a 'slim' PC for an HTPC (idea was to make it
about the size of a 'normal' VCR) and the case was light as a feather empty
BUT, after it was all together I had a real small box that felt like it was
made of solid lead, rather that a large box with a small lead brick in it.
Quite impressive, actually. Almost like a 'trick' case. "My, what a cute
little PC. <pick it up> HOLY HANNAH! What the heck did you put IN there?
gold bars?" hehe (not suitable for LAN parties, btw)

I'm just not sure a small savings in case weight it all that noticeable
even if an acrylic case would be lighter than, say, an aluminum case (I
have my doubts).

However, as I mentioned above, I can't imagine it's the case that's causing
the problem with getting the motherboards to run.

I'm thinking the
extra 5 or 10 pounds will do him some good.

You can always add lead bricks, or gold bars

 

[David Maynard]

The primary purpose of grounding is human safety.

That's true for the typical earthed AC 'appliance' but it's not the only
reason for grounding in electronics (ESD and EMI protection being two
others) and one can easily make a PC with no earth ground. Pick up a
notebook some time.

Chassis
are often metal to avoid EMC problems. Metal creates a
complication; exposed metal must then connectio to safety
ground in circuit breaker box.

A typical PC case is earthed but that is certainly not a 'universal
requirement' for everything. It is only a requirement when the 'exposed'
metal can also come into contact with dangerous voltages and double
insulation is one way to avoid it. Another is to simply not have any
dangerous voltages present and you will note that your typical battery
powered portable device has no 'ground' going back to some circuit breaker box.

How we make that connection is
defined by other problems that can be created when connecting
safety ground to metal chassis.

I have no idea why you want to give the impression there is some
'mysterious' set of "other problems." For a typical PC the PSU is
internally earthed and automatically earths the case when it's bolted in.
Story over.

Black wires from power supply are logic ground for
motherboard and peripherals. Notice an adjective before each
ground. All grounds are unique. And all grounds connect back
to the breaker box - for human safety.

They do in a PC because that is the simple and inexpensive way but, again,
it is not a 'universal requirement' of electronics. The already mentioned
portable devices are one example but another is medical equipment, whose
electronics are electrically isolated from the AC line.

'Connecting' grounds is so current can flow between them and that is not
always desirable. Transformers are one means to separate electrical
systems. Optical isolation is another. And analog flying capacitor inputs
are another where the thing being measured and the measuring device have no
common electrical connection whatsoever.

"Human safety" is only one piece of this pie. An important piece, to be
sure, but, nevertheless, not the whole pie.

How we interconnect
those grounds can cause or avoid other problems.

How come you never mention what these mysterious "other problems" are?

Again, as with the PSU and case, the design issues involved are taken care
of by the designers and an ATX motherboard is designed to be bolted into a
metal ATX case fitted with an ATX PSU. As such, "we" (the user) do not
(normally) decide the "how" to "interconnect those grounds."

Greg has an unusual situation because he has a non-standard, unusual, case
but there's no reason to needlessly confuse everyone with these
mysteriously unspecified "other problems."