Unplugging power cord

[Parish]

Is that better than using a neon screwdriver )

I've always wondered about the reliablity of those with regard to their
failure mode.

The advice is always to check them with a known live source, but how do
they fail? If they fail instantly, like light bulbs, they could work
when you tested them and then when you use them on the thing you want to
check it has failed but you think the circuit you're testing is dead.

Parish

 

[Parish]

http://www.amazon.co.uk/exec/obidos/ASIN/B0000YPUOM/ref=pd_sim_ce_dp_1/202-5872665-8912609

Duh! Must get some new glasses - I read your original post as *eight*
pounds, hence my keeness to know whether it was new

Parish

 

[w_tom]

You are not earthing for anti-static protection. You are
grounding charges on your shoes. Ground and earthing are
different. Connect the anti-static strap directly to the
computer chassis. That way you and the computer are always at
same potential. Put computer on a table top that connects to
floor - where those charges on your shoes are located.
Therefore your shoes will not create electricity paths through
computer.

Never work on a computer connected to AC mains. Never.
That is nonsense about "earthing" for static protection.
Even worse, any power cord connected to a computer means the
power will eventually and accidentally be turned on or left
on. Remove the power cord. Do not even trust a power
switch. Remove power cord.

Ground out charges on shoes. Earthing has nothing to do
with anti-static protection.

 

[Rob Morley]

Jeff Gaines wrote:

I've always wondered about the reliablity of those with regard to their
failure mode.

The advice is always to check them with a known live source, but how do
they fail? If they fail instantly, like light bulbs, they could work
when you tested them and then when you use them on the thing you want to
check it has failed but you think the circuit you're testing is dead.

In my experience they just gradually get dimmer.

 

[Rob Morley]

I'm not an electricl/electronic expert but I'd say yes - why do
components always comw in an anti-stat bag?

To make sure that everything is at the same potential - if they needed
to be grounded then antistatic bags wouldn't work, because they aren't

 

[Parish]

To make sure that everything is at the same potential - if they needed
to be grounded then antistatic bags wouldn't work, because they aren't

I understand that but, without the power lead in the case is not earthed
so you can't discharge yourself through it therefore when you touch a
component you will charge that up to whatever potential you are at which
creates a very large p.d. across the components - doesn't it?

If that's not the case why are you supposed to use an anti-stat wrist
band - connected to earth - when handling e;ectronic devices?

Parish

 

[Michael Salem]

Me:

Is that better than using a neon screwdriver )

Very much so! You only use a screwdriver when you suspect something may
be wrong; but you don't get it out every time you touch the case of a
metal-bodied toaster, for example (a real example). Having spent time in
Latin America, with 220Vac mains, two-pin wiring, and dodgy appliances
(they were expensive, so kept working indefinitely), I got into the
habit of touching anything metal and plugged-in this way before
committing. Even appliances regularly used, and deemed safe, tended to
make your skin tingle a bit.

(Re another posting: I posted this tip maybe 8 years ago, probably in
demon.tech.pc. Someone has a long memory.)

Best wishes,

 

[GwG]

GwG wrote:
...

A possibly life-saving tip: if you touch something electrically live
with your fingers in the normal way, your muscles will contract, making
you press or grip the hazard.

If you stroke it gently with the backs of your fingers, you will feel if
it is live, but the muscular contraction will move your hand away from
the hazard.

I am an electrician, so I am used to letting go quick when things get
hot.
Before this, I would judge the state of the house, and wiring, before
just relying on switching off at the socket. This house was immaculate,
and the wiring/installation looked perfect, which it should have been,
as it had been rewired by the EMEB. I was working on a fridge compressor
at the time, and grabbed hold of the relay to remove it, when ouch!. I
tested the socket feeding the fridge, and found the live & neutral
reversed, then checked the other sockets and found them all the same. I
asked the woman who had carried out the rewiring, and she said the EMEB,
I then advised her to contact them, and I put it in writing for her what
I had found. The next time I saw her, I asked her what had happened, she
said that they sent the same electrician that had rewired the house, and
he just kept apologising all the time he was there, but even though I
did not agree with sending the same lad back that had made such a
serious mistake, it gave me a bit of satisfaction knowing that he must
have been squirming before, during, and after the visit.

 

[Noozer]

I understand that but, without the power lead in the case is not earthed

so you can't discharge yourself through it therefore when you touch a
component you will charge that up to whatever potential you are at which
creates a very large p.d. across the components - doesn't it?

Not if you are connected to the case... then you have the same potential as
the case as there shouldn't be any static jumping. Of course if you happen
to touch something else at the same time you could have problems.

If that's not the case why are you supposed to use an anti-stat wrist
band - connected to earth - when handling e;ectronic devices?

To make sure that there is the least likely chance of a change in potential
and earth is the most commone way to do it.

You don't need to be strapped to the case, just make sure you touch it
before you grab something else.

 

[Parish]

Not if you are connected to the case... then you have the same potential as
the case as there shouldn't be any static jumping.

So, assuming you're charged up with static through walking on a nylon
carpet, you touch the case, which isn't earthed because the power lead
is out, you and the case are now at the same potential. That I
understand, but are you saying that the potential of the case, although
it is at greater than earth potential, is not high enough to damage
electronic devices?

Of course if you happen
to touch something else at the same time you could have problems.


To make sure that there is the least likely chance of a change in potential
and earth is the most commone way to do it.

But it could be any potential, the Faraday cgae effect, yes?

You don't need to be strapped to the case, just make sure you touch it
before you grab something else.

Parish

 

[Rob Morley]

So, assuming you're charged up with static through walking on a nylon
carpet, you touch the case, which isn't earthed because the power lead
is out, you and the case are now at the same potential. That I
understand, but are you saying that the potential of the case, although
it is at greater than earth potential, is not high enough to damage
electronic devices?

As far as the components in the PC are concerned the case is at ground
potential. As long as anything that touches them is also at that
potential there won't be a problem. So touch the case to equalise your
potential, touch any new components against the case before you remove
them from their antistatic packaging, and there's no reason for naughty
electrons to want to rush anywhere and do mischief.

 

[VWWall]

GwG wrote:
...



A possibly life-saving tip: if you touch something electrically live
with your fingers in the normal way, your muscles will contract, making
you press or grip the hazard.

If you stroke it gently with the backs of your fingers, you will feel if
it is live, but the muscular contraction will move your hand away from
the hazard.

Best wishes,

That's an old admonition. I had a friend, that while working on a live
switchboard, remembered to do just that. He hit a live connection and
the muscular contraction doubled up his fist and punched him in the eye.
I suppose a black eye is better than electrocution!

Virg Wall

 

[Parish]

The metalwork on the case is a large enough sink to absorb any static charge
without any noticable change in case potential wrt earth.

Ah, thank you. I was assuming that discharging static from your body to
a case with the mains lead out could raise the potential of the case to
a level sufficient to damage electronic components.

Parish

 

[ToolPackinMama]

A possibly life-saving tip: if you touch something electrically live
with your fingers in the normal way, your muscles will contract, making
you press or grip the hazard.

If you stroke it gently with the backs of your fingers, you will feel if
it is live, but the muscular contraction will move your hand away from
the hazard.

Thank you.

 

[jim.]

As far as the components in the PC are concerned the case is at ground
potential. As long as anything that touches them is also at that
potential there won't be a problem. So touch the case to equalise your
potential, touch any new components against the case before you remove
them from their antistatic packaging, and there's no reason for naughty
electrons to want to rush anywhere and do mischief.

Hiya Rob.
I love it whenever this one crops up.. here's my 2p
It doesn't matter a shite whether the case is coupled via the mains lead to
mains earth or not.
The metalwork on the case is a large enough sink to absorb any static charge
without any noticable change in case potential wrt earth.
A good test is to put on your best rubber shoes, switch OFF your big screen
TV and wipe your hand all over the screen as it goes off.
Then discharge your body to the case, and observe the spark length
with/without the mains lead plugged in.
It's also possible to discharge yourself to some poor unsuspecting persons
ear lobe, but of course I wouldn't recomend that ;-)

 

[jim.]

In my experience they just gradually get dimmer.

Unfortunately they fail to danger, and they're neon bulbs so can go quickly
due to shock damage.
I have had one fail, but they do seem pretty sturdy.
Used to deal with small neons a lot in the old GEC TVs and they went dim,
went out, did all sorts of wierd stuff.
The thing about the tingle on the back of the hand is often a first warning,
but I always put my life in he hands of a neon screwdriver in the overall
pocket.

 

[David Maynard]

Thanks for the replies. Guess I got lucky with my current setup.

It isn't as if it's 'guaranteed' to blow something with standby power
active, but it's possible.

 

[Derek Baker]

It isn't as if it's 'guaranteed' to blow something with standby power
active, but it's possible.

As I always turn off the PSU using it's switch, turns out it wasn't luck.

 

[Bob]

I see in the manual for my new motherboard - an MSI K8N Neo - it says to
remove the power cord when inserting and removing cards and DIMMs.

Is this good advice or excessive caution? With my current board I never did
that.

Plug the PC power cord into a "power strip" that is plugged into the
electrical outlet. The "power strip" is turned OFF. Your PC is grounded,
but it receives no current. Any suggestion that you remove the power cord
is, of course, ridiculous, since there is no grounding path.

 

[David Maynard]

As I always turn off the PSU using it's switch, turns out it wasn't luck.

Yes. Well, that has the same effect, except for the times I've seen people
accidentally turn it back on.

Dern rare to accidentally plug the power cord back in, though.