Grounding

[John]

My daughter is about to replace a memory module. (UK based where we have 3
pin grounded wall sockets (mains receptacles))

What is best -

- Leave the PC plugged into the grounded wall socket (but switched off) and
keep in contact with the case of the PC to remove static?

or

- Unplug the PC and keep in contact with the case (on the understanding that
she will be at the same potential as the case - but not necessarily grounded
to earth)

 

[Paul]

My daughter is about to replace a memory module. (UK based where we have 3
pin grounded wall sockets (mains receptacles))

What is best -

- Leave the PC plugged into the grounded wall socket (but switched off) and
keep in contact with the case of the PC to remove static?

or

- Unplug the PC and keep in contact with the case (on the understanding that
she will be at the same potential as the case - but not necessarily grounded
to earth)

The best way, is to use one of these. This is a disposable wrist strap.
On one end, is a shiny copper section, with an adhesive applied to a portion
of it. You stick that end, onto a shiny screw that bites into the chassis
metal somewhere. (I use a screw or rivet on the PSU.) The idea is, the copper
end of the wrist strap is at chassis potential. I've actually used the same
disposable wrist strap a number of times, so you don't have to throw it away
until it gets grubby.

(Order one when you buy memory...)
http://www.crucial.com/store/partspecs.aspx?imodule=CTWRISTSTRAP

With the other end wrapped around your wrist, there is a high resistance
connection between you and the computer chassis. Perhaps somewhere around
1 megohm or so. The purpose of the high resistance, is to slowly drain
ESD off your body. (A fast discharge = high current flow, slow means a lower
magnitude current during equalization.) Then, pick up the ESD packaged DIMM,
open the package and install it.

If you don't have a strap, you can...

1) Put on a pair of summer shorts. This leaves bare legs.
2) Unplug computer, lay it in your lap. Remove the side panel, lay panel on the floor.
By the computer laying in your lap, part of the chassis touches bare skin,
bringing you to the same potential as the chassis. Touch shiny metal on
the chassis to be doubly sure.
3) Snip open DIMM package. Hold DIMM by edges (not the contacts). Finger
oils and salt are not good for the contacts. Insert DIMM
into slot. Check clips have snapped into the correct position.
4) Put the side panel back on. Plug in and test.
5) If DIMM is not detected, or programs like memtest86+ fail almost
immediately, you can...
6) Put the computer in your lap again. Make sure you are at the same potential
as the rest of the chassis. (Computer is unplugged, to ensure no +5VSB
is present.) Then, remove and reinsert the DIMM about five times. The removal
and insertion will help clean manufacturing dirt from the socket contacts.
The aqueous wash at the factory doesn't necessarily remove all debris. Avoid
the temptation to use other cleaning techniques. Removing precious gold from
contact surfaces is self defeating.
7) Put the side panel on again and retest.

A DIMM slot is powered (indirectly) via +5VSB. That is so, when a computer is
in sleep mode, the memory has power to help keep it refreshed. You don't want
to plug a DIMM into a slot which is electrified. Yes, you can flip off the
switch on the back of the computer, and *most* of the time there will be no
DC power inside the chassis. We've had one report here, where a cheap supply
continued to run, even when the switch was flipped to the off position (a
broken switch). Even though that is a remote possibility, unplugging the
computer guarantees there is no DC present inside the chassis. Wait at least
30 seconds after unplugging, before inserting the DIMM. My computer needs
about 30 seconds for all power to be drained by the standby loading. Then
it should be safe to work on a DIMM.

HTH,
Paul

 

[wasbit]

My daughter is about to replace a memory module. (UK based where we have 3
pin grounded wall sockets (mains receptacles))

What is best -

- Leave the PC plugged into the grounded wall socket (but switched off)
and keep in contact with the case of the PC to remove static?

or

- Unplug the PC and keep in contact with the case (on the understanding
that she will be at the same potential as the case - but not necessarily
grounded to earth)

After seeing the way that memory strips are thrown into a box and rifled
through at computer shows I doubt there is anything worse that you could do.

Although I no longer bother to take precautions when working on my own
computers apart from turning off the power, it would be wrong of me to
advise you to do the same.

 

[kony]

My daughter is about to replace a memory module. (UK based where we have 3
pin grounded wall sockets (mains receptacles))

What is best -

- Leave the PC plugged into the grounded wall socket (but switched off) and
keep in contact with the case of the PC to remove static?

or

- Unplug the PC and keep in contact with the case (on the understanding that
she will be at the same potential as the case - but not necessarily grounded
to earth)

The basic strategy is as follows:

1) Case should be connected to ground through the power
cord. (this is optional, but the easiest way when PSU has
an on/off switch).

2) User should be connected to ground through high
impedance (ESD strap or touching metal with serial megaohm
resistor connected to ground).

3) User should not be touching the system case when the
memory module is picked up, but should be electrically
connected through the ESD strap or megaohm resistor to
ground... to earth ground if the system is connected to
earth ground, or to system chassis ground if the system is
not connected to earth ground (like if the AC power cord has
to be unplugged because the PSU has no on/off switch).

There are three "bodies" here all possibly at a different
potential. Human, system, and memory module. Having the
system grounded to earth through the AC electrical system is
sufficient, so what remains is whether the memory module
itself is at same potential as the system, at ground
potential - but it is not enough to be touching the system
case because the case and memory module may not be at the
same potential yet. If earth ground through the AC outlet
is not possible, then connecting the ESD strap or megaohm
resistor to the system case serially and then touching the
memory will be sufficient.

What will not be safe is to have the case grounded, be
directly touching the case (with or without the ESD strap)
while picking up the memory module. So earth ground is not
important, but to slowly bring the memory module to the same
potential as the system ground is important. Earth ground
is just a very convenient reference.

 

[Mike Walsh]

Many people recommend that the PC be unplugged. This is primarily because when the PC is "switched off" there can still be power on the motherboard. It is better to leave the PC plugged in so that it is grounded and remove all power by turning off power at the power supply, power strip, or UPS.

 

[Plato]

My daughter is about to replace a memory module. (UK based where we have 3
pin grounded wall sockets (mains receptacles))

What is best -

- Leave the PC plugged into the grounded wall socket (but switched off) and
keep in contact with the case of the PC to remove static?

or

- Unplug the PC and keep in contact with the case (on the understanding that
she will be at the same potential as the case - but not necessarily grounded
to earth)

Unplug the PC when installing ram, or any other card.

 

[sandy58]

My daughter is about to replace a memory module. (UK based where we have 3
pin grounded wall sockets (mains receptacles))

What is best -

- Leave the PC plugged into the grounded wall socket (but switched off) and
keep in contact with the case of the PC to remove static?

or

- Unplug the PC and keep in contact with the case (on the understanding that
she will be at the same potential as the case - but not necessarily grounded
to earth)

Read Plato! Anyone reading these replies would think the OP was
attempting to evade old Smokey (the electric chair) doing it's job, or
even HELP getting zapped. If anyone is SO unsure of how to go about
this op...LEAVE WELL ALONE! Get someone who knows to do it.

 

[Calab]

This is what I do. Just be sure that the PC is switch off at the BACK. If
your PSU doesn't have a power switch, then unplug it from the wall.

 

[Lord Turkey Cough]

My daughter is about to replace a memory module. (UK based where we have 3
pin grounded wall sockets (mains receptacles))

What is best -

- Leave the PC plugged into the grounded wall socket (but switched off)
and keep in contact with the case of the PC to remove static?

or

- Unplug the PC and keep in contact with the case (on the understanding
that she will be at the same potential as the case - but not necessarily
grounded to earth)

Don't make much difference, but safest to switch it off and unplug.
Memeory modules are cheaper to replace than your daughter.
Then eart against the frame.
Don't forget to wear wellingtons,

 

[Guest]

My daughter is about to replace a memory module. (UK based where we have 3
pin grounded wall sockets (mains receptacles))

What is best -

- Leave the PC plugged into the grounded wall socket (but switched off) and
keep in contact with the case of the PC to remove static?

or

- Unplug the PC and keep in contact with the case (on the understanding that
she will be at the same potential as the case - but not necessarily grounded
to earth)

The former is prohibited for safety reasons at the factories I've
visited.

The latter is safer and maybe even better for preventing damage, but
wear short sleeves to improve the likelihood that the forearms will be
in contact with the metal case, and to prevent static buildup on the
person, wear no shoes, socks, or stockings.

Google "ESD" (electrostatic discharge) for more information on proper
techniques.

 

[GT]

My daughter is about to replace a memory module. (UK based where we have 3
pin grounded wall sockets (mains receptacles))

What is best -

- Leave the PC plugged into the grounded wall socket (but switched off)
and keep in contact with the case of the PC to remove static?

I always do this - you are grounded through the earth pin.

 

[kony]

I always do this - you are grounded through the earth pin.

.... but doing that isn't enough.

The only way to be sure there is no chance of ESD damage is
to slowly bring all parts to the same potential. By
touching the PC case, a metal portion, you now have brought
yourself to the same potential as system ground, but what
has not happened yet is to bring the new memory module to
that potential.

In other words, if the memory module or packaging is holding
a charge and you reach out and grab it while touching the
system case, you have created a discharge path through
yourself which could damage the memory.

 

[larry moe 'n curly]

My daughter is about to replace a memory module. (UK based where we have 3
pin grounded wall sockets (mains receptacles))

What is best -

- Leave the PC plugged into the grounded wall socket (but switched off) and
keep in contact with the case of the PC to remove static?

or

- Unplug the PC and keep in contact with the case (on the understanding that
she will be at the same potential as the case - but not necessarily grounded
to earth)

You're supposed to avoid the first method because a direct connection
between a human and ground is a no-no, in case the human also touches
something conductive with high voltage on it and the current flows
through the heart to ground. That's why anti-static wrist straps have
one megaohm of resistance in series with their ground connections.

The easiest way to avoid zapping any computer stuff is by covering the
whole desk with pink anti-static bubble plastic or foam sheet and
laying everything atop that. Then, by working in short sleeves to
stay in almost constant contact with the pink stuff (mostly through
elbows) and not shuffling around too much, it's a cinch to avoid
static build-up.

 

[GT]

... but doing that isn't enough.

The only way to be sure there is no chance of ESD damage is
to slowly bring all parts to the same potential. By
touching the PC case, a metal portion, you now have brought
yourself to the same potential as system ground, but what
has not happened yet is to bring the new memory module to
that potential.

not something I have ever enountered. According to this statement, picking
the object up will always bring it quickly/instantly to the same potential
as you regardless of whether you are grounded or not. So how can this be
done slowly by the normal home user with no special equipment?

 

[kony]

not something I have ever enountered. According to this statement, picking
the object up will always bring it quickly/instantly to the same potential
as you regardless of whether you are grounded or not. So how can this be
done slowly by the normal home user with no special equipment?

It depends on how you define "special equipment". A typical
low cost ESD protective wrist strap, mat, etc, has a high
resistance between it and it's ground clip (or earth ground
lead, depending on how it's designed, and if an earth ground
lead then the other parts are also referenced to earth
ground else the clip is clipped onto the other parts'
isolated ground).

If you have the wrist strap clipped to the system ground
then you are draining the charge (equalizing potential is
more accurate way to put it) from the (memory in this case)
part at lower current than if you were directly touching the
system ground/chassis with your hand.

IOW, if you had no wrist strap I suppose you could fashion
something yourself using a 1MOhm resistor, or as close to
that value as reasonably possible. Some types of antistatic
bags are made different than others. The type that looks
metallic may have high resistance, the type that looks like
it has black grids running all over it is roughly the right
resistance so if the part were in such a bag it would be
effective to grab the bag while earth grounded which would
bring the part inside to the same potential safely before it
was removed from that bag, or at least close enough.

 

[Strobe]

not something I have ever enountered. According to this statement, picking
the object up will always bring it quickly/instantly to the same potential
as you regardless of whether you are grounded or not. So how can this be
done slowly by the normal home user with no special equipment?

Most ESD-sensitive components are shipped in special conductive packaging.
Just hold the package for a little while, and the component reaches
your potential safely. If you were also touching the PC chassis,
there's now zero volts between the new RAM module and your PC.

 

[kony]

Most ESD-sensitive components are shipped in special conductive packaging.
Just hold the package for a little while, and the component reaches
your potential safely. If you were also touching the PC chassis,
there's now zero volts between the new RAM module and your PC.

While it is true many components ship in conductive
packaging, some ESD protective packaging only has antistatic
(creation) coating not a conductiveness, and unfortunately
most memory these days seems to be shipped in an insulating
plastic shell-like container that will not offer any
protection, the memory is still vulnerable the moment it's
being removed from this insulating package.

 

[GT]

It depends on how you define "special equipment". A typical
low cost ESD protective wrist strap, mat, etc, has a high
resistance between it and it's ground clip (or earth ground
lead, depending on how it's designed, and if an earth ground
lead then the other parts are also referenced to earth
ground else the clip is clipped onto the other parts'
isolated ground).

But when you pick up the +ve charged item and your body is -ve charged or
even neutral, what prevents a fast discharge between the two bodies? Won't
this happen regardless of how your wrist is grounded?

This isn't something I have ever done... but you could pick up the object
using rubber gloves (washing up gloves) and connect it to the grounding
strap for a while to neutralise things, then remove the gloves and carry on
with the wrist strap attached to your wrist.

 

[kony]

But when you pick up the +ve charged item and your body is -ve charged or
even neutral, what prevents a fast discharge between the two bodies? Won't
this happen regardless of how your wrist is grounded?

If the part is left in the ESD safe packaging it shouldn't
have much if any charge, this is one reason why having case
at earth ground can be better (easier) than floating ground
so the relative potential of the user and case is at a known
level. The first step in ESD damage prevention is the
attempt to prevent any object including installer from
having a high charge relative to ground.

The package may be designed to dissipate slowly, part is
left in the packaging until ready to install, and if the
packaging is only designed to prevent generation of static
(non-conductive) then it would be even safer to use an ESD
mat connected to system ground or earth ground if system is
likewise, sliding out the part onto the mat. There are
varying levels of precaution depending on perceived need and
sensitivity of the part. Going even further one might have
treated carpet, be mindful of clothing worn, raise the
humidity in the room.