If you're thinking of opening 'the box'...

  Bacon & Eggs 11:04 15 Apr 03
Locked

...I would have thought it was common sense to unplug it first. However it appears not everyone thinks so!!

New guidelines on how not to fry yourself and your PC by way of the Register.

click here

  Ben Avery 11:16 15 Apr 03

What you have to remember is that if the PC is plugged in the plug socket but SWITCHED OFF the only connection which is still made is the earth connection. When you switch off the plug socket the Live & Neutral wires are disabled from the plug but the earth remains in tact - this is a safety feature in all homes (unless you live in the continent where sockets are double insulated and have just the brown and blue (live & neutral) wires and no seperate earth wire (you also get this in many lamps and hi fi parts etc.)

When working on the inside of a PC the safety way to earth yourself is to use an anti-static wrish strap - the professionals will even use a wrist strap which plugs into the household plug socket!

The reason for this is that you will not get a better earth than the one in your household socket so you may as well utilise this.

Whenever I play around inside my PC, I ground myself to the PC chassis and leave it plugged in but switched off at the wall. This way I'm earthed to my house earth circuit through the PC chassis.

Doesn't get mush safer than that!

BA

  Ben Avery 11:23 15 Apr 03

as mentioned by the HSE, you do rely upon the Household socket not failing!

However, if your household mains failed in this way the chances are there would be other consequences from it too, you may even find other items in the household which are deemed "safe" like radiators, copper pipes etc, recieving an electrical charge which makes them no more safe than the plug socket!

The procedure posted above is not advice which I want anybody to take, it's just how I was taught to do it by the electrician and computer tech's I've worked with.

However, if the HSE say that this is not safe, then do it their way! Don't forget though that the safest way in my opinion is to use a cable like me, which only has an earth lead in it (no live or neutral)! I forgot that in my posting.

If the earth of your house becomes "live" then anything metal in the house will be live also so it makes no odds to me.

BA

  Bacon & Eggs 11:30 15 Apr 03

Believe it or not, the plug socket that my compuet is plugged into doesnt actually have an on/off switch... however the multiway adaptor does and the PSU does..

I agree that the house earthing has to be the best one there is to use, but i didn't know about straps that just plug into the earth.

Interesting, anyway... I wonder how many PCs the HSE experts have ever built?

  graham 11:33 15 Apr 03

Sorry, but you are wrong! A domestic socket only switches off the live circuit; if there is a wiring error somewhere it may be the neutral that is being switched off, leaving live and earth still connected to your PC. Play safe and unplug. You should bear in mind that the main thing is that you and the PC are at the same potential. If your PC is earthed, chances are that you are not, due to static from your clothes or carpet.

Simply touching the (unplugged) metal chassis is all that is required.

  Tog 11:39 15 Apr 03

You can buy "Earth Only" mains plugs that are designed for connection to wrist straps. (RS Components part number 250-4172 )
The HSE comment on the uncertainty of the condition of the wiring in the mains socket could equally apply to professional workshops and field service equipment. Bit odd. I think they may be concerned that a home made version would not include a suitably rated 1Meg safety resistor.

  Belatucadrus 11:40 15 Apr 03

To quote the register "The HSE warns that this procedure can be dangerous. If there is a fault in the computer power supply, or if the electric socket is wired incorrectly, the computer chassis can become live and give a fatal electric shock." If the chassis is live, it's highly likely the case will be to ( I know, metal cases only ) and you aren't going to need to open it to get shocked. I could be wrong, but I also suspect that a PC with a live chassis has probably already toasted a significant number of it's components. Not something I care to test.
I think the HSE is overreacting, but it highlights the need to ensure your electrical earth works as advertised and the necessity to treat elecricity with great care.

  tbh72 11:56 15 Apr 03

Let me tell, computer's that bite back are no fun at all!!! I remember building an old AT type PC, & if I recollect correctly the was a problem with the power button "The one that has four wires connected"...... From what I can remember I was only touching the rubber shielding around one of the wires, needless to say..... My heart felt like it was gonna EXPLODE!!!!!

  Sir Radfordin™ 12:23 15 Apr 03

Ho hum, someone will always spoil the fun.

Have just finished re-building a PC with the case off, my hands inside, cables plugged in and taken off again. Don't seem to have suffred for this yet! Oh, and I didn't even turn the mains off.

  MAJ 12:54 15 Apr 03

Ohh the number of times I have taken off sockets only to find that the 2.5mm earth wire has been broken and is no longer connected. That's why I always advise people not to rely on the "keep it plugged in but turned off" advice. I usually grab hold of the copper pipe under the kitchen sink as it is directly earthed to the main curcuit board in the house, usually with a 10mm earth wire. So far nothing fried due to static.

  Ben Avery 13:00 15 Apr 03

I think that people who are very new to the building/upgrading of PC's will be the ones who this advice is meant for. The HSE has to be seen to cover it's back - fair enough. But the fact is that most professional Computer Technicians who spend all day in and out of the indide of PC's use an anti-static wrist strap which plugs directly into the mains.

I find it hard to believe that the companies who make these products would be allowed to produce something which is a safety hazard, don't you?

I have only ever had an electric shock from a household socket once and that was my own fault (I was fixing a PA system and didn't check whether it was switched off - it wasn't, neither at the mains or the unit -lesson to be learnt: DON'T RUSH!) and do not see this "warning" as a serious problem so long as you are taking the correct precautions.

If you feel the need to play it safe, simply strap yourself to the metal chassis with the PC unplugged - no way of getting a shock then. Your earthing will not be as good but will likely suffice.

BA

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