why to ground a computer

Sir,

You refer your previous poster neutral voltge.This is not due to touching of live parts.Your computer system is ok.Any computer you purchase it needs earthing for for electro magnetic induction.Otherwise you will get shock.All your key board terminals is one of the contact for communication to server.So you should run it with dedicated earthing not with combined parallel earthing.

Thanks for ur help.

But sir does electro magnetic induction produce current?

I replied to your previous post. In your computer you have a power supply, this relies on a connection to ground to get rid of harmonic currents. (Inside is a switching circuit, the voltage you feel is caused as a result of induction).

The thing that causes current to flow is a voltage, if you are getting shocks current is flowing through you vecause you are at a different voltage potential from your computer. If you have no earth connection on your supply you still have to provide a path for these currents. Therefore you must identify the neutral from your phase and neutral, and connect your computer earth to this. Also ensure your phase and neutral are connected the right way round before you do this. If you are unsure, ask for help from someone who understands and is in the same room as you and not at the other end of a computer.

I once wired in a computer room, each computer produced quite a few mA of leakage current. I put an ammeter in series and switched on each computer in turn and watched the total leakage current rise. It was significantly more than was allowed for the RCD and I had to split the circuits and provide two protective devices. I also disconnected the earth and measured the potential of this computer "earth" to electrical earth, it was over 90V. In this case the earth was serving both functional and protective functions.

It sounds like you have a serious problem with the electrical supply to your home, this should stop your computer shocking you, but you must be in contact with some electrical potential in order to receive a shock in the first place, think about this. Talk to someone who can help. To eliminate the possibility your computer is faulty, which although unlikely has not been ruled out, you could take it to a house with a functioning earthed electrical system and try it there to see if you get shocks (not really - use a meter)

< I put an ammeter in series and switched on each computer in turn and watched the total leakage current rise.>

dear sir,

u measured the current between which points.

<I also disconnected the earth and measured the potential of this computer "earth" to electrical earth, it was over 90V.>

u measured the voltage between which points.

There may be nothing wrong with your computer, and the wiring is quite okay..

The problem is that a computer is a class 1 graded appliance and needs an earth for safety reasons.

The mains inlet to the power supply will almost certainly have a mains filter in its path , this filter will have capacitors connected from neutral and live to the chassis, the metalwork. if there is no earth then this current flowing through the filter capacitors will flow through you!!

Causing a slight electrical shock - solution is to earth the chassis as the manufacturer intended for safety and interference reasons.

John.

between the earth conductor from the ring circuit and the electrical earth for the supply. I just broke the earth connection, in the first case it was a (moving coil) ammeter, and in the second it was a voltmeter, between the same two points. I then restored the earth connection.

As you have read : a computer HAS GOT TO BE earthed for several reasons.

I would go to your landlord and insist that he provides a good earth. (not just a wire connected to the water pipes/system) If he refuses : sew him !

(in my country it is illegal to not providing a good earth system. Electricity companies are not allowed to deliver power if there's not a good and tested earth)

Slightly off-topic.

Please don't take this as an insult to your English...just a minor correction.

sew - to unite or fasten by stitches

sue - to seek justice or right from (a person) by legal process; specifically : to bring an action against

I did get a little chuckle when I envisioned sewing a landlord.

[ Replying to one-and-all ]

"As you have read: a computer HAS GOT TO BE earthed for several reasons."

I'm working on my third (laptop) computer --- NONE of which had ever been produced with a ground lead_.

Can "WE" {i.e., SOMEBODY} be a smidge more specific about what SPECIFIC DISCREET COMPONENT causes the problem-at-hand (with desktops only, obviously)?

e.g.; what induces voltages to be present in those external peripherals as they are(?)

And, how about adding: "What modification(s) might be made by the manufacturers, or by the do-it-yourselfer, that would alleviate this peculiarity...?

_________________________________________________________

Lap top ...Of course not ... But you didn't connect the earth to the PSU ? and we're talking about metal desktopcomputers here.

The dangerous point is not the power input of the computer. In the powersupply there are voltages to up to and over 300V DC! if this voltage touches a metal case what is not earthed, you gonna see sparks when you touch it ... This is lethal !!!

If you don't earth computer, the whole circuit might be on a high voltage level (yes, even could be 1000's of volts. Again, this is dangerous for the user, but also the (very delicate) circuitry of a computer can easily get destroyed.

So : Earth, earth, earth that thing !!!

Another thingabout earthing a computer :

it wouldn't be the first motherboard that I have to replace because "static" destroyed it ...

And probably if something goes wrong with your newly bought computer, and your vendor knows that it not has been earthed, you'll probably gonna loose your warrenty...

So : EARTH that thing !!!

A very important reason to ground or earth your computer is that the transient overvoltage protection (MOV sometimes Gas Tubes) rely on ground being available to function correctly this is also true for ESD protection as well.

I agree 100% with everyone about how important a ground is. The National Electrical Code (NEC) in the US however will allow ungrounded circuits if they are feed through a Ground Fault Circuit Interrupter (GFCI) which is available for under $20 and a label is applied which states: "No equipment ground" to the downstream receptacles.

A laptop charger is not supplied with a ground but the printer and external modem you hook to it does and they could have internal faults which need to be drained to ground. Also, have you ever noticed a spark leap from your fingers on a dry winter day? If you touched your laptop without discharging the static in your body to ground, you may be buying another laptop. During assembly workers wear grounding bracelets to drain off static and the unit is not even powered up! And, as was already mentioned, the MOV's in a surge protector will not offer as much protection if not grounded.

I believe that a few points have been forgotten:-

DO NOT USE A NORMAL PC WITHOUT A PROPER EARTH CONNECTION. It can be dangerous.....

A Laptop (like many different machines with a 2 wire power cord), is usually "Double Insulated", therefore it does not usually need an earth (My Toshiba Laptop from 2006 DOES have an earth connection - 3 wire mains cable - funnily enough to the external power supply, but that is seldom!)

Summing up, if it only has a 2 wire cord, you are OK....3 wire, not OK - assuming no proper earth in the building.

Same with hi-fi equipment. Some are double insulated and if you earth them, you get a rather annoying humm over the speakers.

With things like this, which is basically for safety, you do not ask daft questions or worse, deny the reasoning. You just earth it and be happy

Exceedingly well put!

There is NO-REASON WHY in Safety procedures at all. One thing
To ask question is another thing.

Have faith but study why?

All mains operated Computers use SMPS [Switch-mode-Power-Supply] which do not use transformer to Isolate Power-Line from the structure [including PCB & Casing]. Technically it is called Galvanic-Isolation.

As for as the "Feeling of Shock" NOT SHOCK is concerned is due to reversing of N & Live some-where in Power-connectors, Wall-Socket or Extension-Lead [if used].
Just reverse the plug in Wall-socket; if non-polarised. Otherwise correct the error where it is.

Power-Inlet of PCs are Polarised & all else should be. This normally faced where 2-pin fixture is used.

Do you think that a USB Stick can give an electric-Shock-Feeling or [Shock]?

Just plug-in the stick [in non-grounded PC] while touching the shield of connector !!!!!

I favour:

" One who asks a question is a fool for five minutes; one who does not ask remains a fool forever. "

I'm a not up to speed on switched mode power supples, so maybe am making a silly comment, but I thought that switched power supples had a relatively tiny isolation transformer, because of the high frequency, a big one is not needed....

Dear Sir.

It is in the out-put for low voltages +12V, -12V, +5V & all.

Mains directly rectified by Bridge rectifier [4 Diodes. & (-) of primary rectifier is common Chassis.

More over Over-voltage protectors 2nd end goes to Common Ground

Regards

Are you telling me that a switched mode power supply output (or at least some of them in the case of a PC) have no complete isolation from the mains input voltage?????

Ho ho hoooo ... There seems to be a serious misunderstanding here... Maybe a short explanation about how switched power supplies work.

The 230VAC mains, (or in some developping countries 110VAC) is rectified to obtain about 300VDC. This 300V gets chopped in little pieces (usually around 100KHz). Because of this high frequency, there is not much need for iron in a transformer. (see formula's to calculate a transformer) But there IS a transformer. Be it a small one (saves copper and iron), but there certainly IS a one. The output of the PSU is galvanic separated of the mains.
Now, another thing that I read in this subject is completely wrong. The negative, nor the positive of the 300VDC is connected to the chassis (ground) of your computer. This would be MURDER ! If your computer is well earthed, this wouldn't cause any danger. But just suppose some one plugs his computer in a non (or bad) earthed socket. (and how many % of the computers are not properly earthed, you think?....) I can tell you : the damage that PLUS 300VDC or MINUS 300 do to your body are exactly the same : DEATH !

So in the first place computers have to be earthed for SAFETY reasons. If some component in your power supply touches the chassis, the (high) voltage is directly short circuited to earth potential -> the same potential as your body. So in case of touching : there is not gonna be any current flowing through your body.

In many cases, the zero potential of the output of your PSU is grounded. This is not because of safety reason (never heard that any one got injured by touching 5 or 12 VDC...) but because you should have a good reference for your 5 and/or 12 Volts.
If the output of your PSU is not grounded, it could happen that the zero volt line actually carries a voltage of e.g. 1,000VDC and the +5V line is on a potential of 1,005 VDC. In theory your computer would run normal. But because there might be lost of variation on this high voltages, and because your computer is build with very sensitive parts, the slightest variation in voltage will kill some components.

Oh yes ... Laptops ... actually it is the same story. Primary circuit of the PSU is NOT grounded, but protected by the earth connection. The minus of the secondary circuit of the power supply is usually earthed.

In any case : PLEASE EARTH YOUR COMPUTERS. It is necessary ! It will prolongue the life of your compter (lap- or desktop) and it also will prolongue YOUR life !

Thank God you chipped in with your seemingly (at least!) perfect explanation.

I thought that Hajee (?) was completely off course, but unsure of what is really right! He should read carefully what you wrote and try and learn something correctly, he often makes such mistakes! It would appear that he has enough knowledge to be REALLY dangerous!!! I rarely bother to read what he says and now I will completely ignore him....thanks for putting me straight.

Everything you said blends in with my imperfect knowledge in this area so many, many thanks indeed! I am sure that many others are also relieved to know that they will not drop dead by touching only 5 or 12 volts inside the computer!!!

My reply to: #25

#20 In reply to #19
" .. had a relatively tiny isolation transformer ... "

My reply:

#21 In reply to #20
" . It is in the out-put for low voltages +12V, -12V, +5V & all. "

Note: This is the Output Transformer which provides "COMPLETE Galvanic ISOLATION" to Outputs

#22 In reply to #21
Are you telling me that a switched mode power supply output (or at least some of them in the case of a PC) have no complete isolation from the mains input voltage?????

#25 In reply to #23

" ... they will not drop dead by touching only 5 or 12 volts inside the computer!!! "

How you derived that I said somewhere in my posts that Out-puts are not ISOLATED..

And I up-hold that in PCs PSUs PRIMARY-RECTIFIERs out-put is NOT completely ISOLATED from Chassis.

Thanks for your KIND remarks.

My reply to:
44mEurope #23 In reply to #21

" ... Be it a small one (saves copper and iron), but there certainly IS a one. The output of the PSU is galvanic separated of the mains. "

My reply to:
#21 In reply to #20

Dear Sir.
It is in the out-put for low voltages +12V, -12V, +5V & all.


" Now, another thing that I read in this subject is completely wrong. The negative, nor the positive of the 300VDC is connected to the chassis (ground) of your computer. "

My reply:

Will you please read my post again which says:
#21 In reply to #20

" ... Mains directly rectified by Bridge rectifier [4 Diodes. & (-) of primary rectifier is common Chassis. ..."

[4 Diodes. & (-) of primary rectifier is common Chassis.

repeated
[4 Diodes. & (-) of primary rectifier is common Chassis.

repeated
[4 Diodes. & (-) of primary rectifier is common Chassis.

Hmmm ... I can't be sure if there's something wrong with your comp. It COULD be, but not necessarily ... Except all the things I mentionned before there's also something like "static" electricity. In this case there are again two possibilities. Or the static is generated by your computer. (spinning fans, harddisks etc ...) But it also could be that your body is static and the shock you feel is not coming from but going to the metal mass of your comp.
Nevertheless ... Earth your comp. If it is too difficult to run an earth wire to an earthpin in the ground, then an alternative is to connect the frame(case) of your comp to a waterpipe. I know this is not really "kosher", but I guess this is better than nothing.

And, by the way, if you are going to tell the vendor of your new comp that you use it on a non earthed circuit, he'll probably will deny any warranty claim, now and in the future. Most likely you're gonna find a text on your comp, or in the manual that this apparatus MUST be earthed.