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What is Static?

Before handling electronic components, it's important to realise that semiconductors can be damaged by high voltage "static electricity" carried on your body. The explanation I shall give is not quite technically correct but it will give you the general idea and allow you to understand the problems much better than a more involved discussion might.

You have probably all seen a Van de Graaf generator at school or at science fairs. It has a moving rubber belt which transfers electrons from its base to a metal globe. If you touch the globe you will receive an electric shock because your feet are on the ground at zero voltage and your hand is touching the globe (not for long!) at 100,000 volts. The potential difference between your feet and hand is 100,000 volts.

However, if you first stand on an insulating block, your whole body will be charged to 100,000 volts when you touch the globe. You feel no painful shock because the potential difference is now between you and the ground - and unless you touch the ground, no current can flow. Your body remains charged to 100,000 volts and your hair tries to escape!

van de graaf generator illustration

If you are wearing shoes with insulating soles or standing on an insulator such as a nylon carpet, your body can hold a charge for a long time. How does it become charged if you don't have a Van de Graaf generator? There are many ways and here are just a few:

1. Run down stairs with your hands sliding along the bannisters. If the bannisters have a nylon coating or are of varnished wood or of plastic then you will wipe electrons off and transfer them to your body which then holds them as an electrostatic charge.

2. Take a piece of clothing out of a plastic bag. Unroll a plastic dustbin liner bag. Remove a nylon garment. Handle expanded polystyrene packing material. All of these items carry a charge which you will "wipe off" onto yourself.

3. Get into a car and shuffle about on the nylon seat cover. Have the air conditioning blow air at you (full of charged particles). Now step out of the car and touch the car or some other metal object. (Sorry, it hurts, doesn't it!)

4. Go into a dark room with a roll of adhesive tape. Wait until your eyes become accustomed to the dark. Now peel a length of tape off the roll. Can you see the blue light as the tape separates from the roll? Separating any pieces of plastic like this will usually produce a discharge of static electricity.

5. Wear two layers of clothing made of synthetic fibres. Move around a lot so the layers move against each other. This movement will build up a static charge on YOU. Now touch a large metal object. Ouch!

Ok, you get the general idea. It's easy to charge yourself up.

How do we protect vulnerable components?

Integrated circuits and transistors have several connections. If ALL of these connections are at the same voltage, there is NO potential difference across them and no damage will result. However, if just one of the connections sees a different voltage from the rest, damage may occur. Some components can be damaged by just a few volts. We protect them by connecting ALL of the pins together. This is quite easy to do. We can wrap them in aluminium foil, for example, or we can press the pins into a conductive material such as carbon-filled plastic foam.

What we should NOT do is expose these components to charge-carrying materials such as plastic bags, expanded polystyrene, polythene, self-adhesive tape or labels being peeled off or ourselves unless we are at the same voltage as the components.

The safest way is to make sure that the component is placed onto a conductive surface before removing it from its protective foam or bag. Then we should touch the same conductive surface before touching the component. Now everything is at the same voltage. There is no potential difference between the component and anything touching it.

This is a simplified explanation. If anyone wants to suggest better wording, please tell me.

Replacing computer memory safely - click HERE

Electric shocks in the house/office

Dear Martin,

I saw your website and was impressed it seems to be very user friendly and inviting.

I do not really understand much about electronics etc, but my wife is suffering from a static electricity problem which I can't really help her with nor even explain to her, if you can shed any light on the subject or come up with a possible cure we would gladly send you some stamps or even money(I would prefer stamps she has other ideas).

Sue my wife has over the past few months started really suffering with shocks "mainly whilst cleaning our house" every time she touches a metal object. I have had the Hoover checked out it's ok and the house wiring is in good order. We haven't had any new carpets for a while, I just can't explain what's happening.

Sue has become more and more worried about it as it is also happening when she cleans at my mothers house, our 8 year old daughter will not let her brush her hair as she gets shocks from her.

I must admit to sort of turning a blind eye to it until she brushed past me in the bedroom (which has a wooden floor) and I got a hell of a belt from her I suddenly decided to start seeking advice which varied from permanently wearing rubber gloves etc"not really practical" to regularly earthing her which again is not really an ideal solution.

Are some people more susceptible than others and what is it that could have altered over the past year, is this a common problem?

I will fully understand if you do not reply as this is probably not really in your line of work but if you can be of any help or offer some basic advise we would be very grateful. Please bear in mind we are not at all clued up on electronics and some of the terms used "we will not be at all offended if you reply in very simple layman's terms."

Yours hopefully,

Kev & Sue

Personal discharge of static electricity

I'm pleased to report that your wife has no special physical properties - other than those for which you married her! (Beauty etc. :o)

Static electricity has nothing to do with the electricity supplied by the mains network or even batteries.

You probably remember experiments at school where you rubbed a plastic rule with cloth and generated an electric charge, which allowed the plastic to attract small pieces of paper? Well, OK, you can try this with a plastic rule. Simply scrub it hard with a pair of nylon tights and hold it over a few tiny scraps of paper. Now run the back of your hand above it and feel the hairs stand up.

That's basically what's happening to your wife. But don't panic! Read on.

To create this "charge" you need a couple of situations.

1. The air has to be quite dry. Air conditioning helps. So does winter when the air is not as humid as in summer. Moist air tends to discharge things that are charged. To prove this, charge up your plastic rule then breathe on it along its length, both sides. It will no longer be charged.

2. You need two pieces of insulating material moving against each other. The best materials (as you've found) are nylon and most other plastics. The effect is very pronounced if you wear nylon tights or stockings and synthetic fibre dress or trousers. Or rather, if your wife wears them!

With a man, the effect is more common with a nylon shirt and a synthetic fibre sweater. Try taking the sweater off in a dark room. You'll actually see blue sparks.

Another common cause of complaints is the "brushed nylon" seats in a car. If you wear synthetic fibre clothing and shuffle in your car seat, when you leave the car you'll get a tremendous shock as you touch the metal door.

Anyway, that's the simple explanation without going into technical discussions involving molecules, atoms, electrons and all that rubbish.

As for THE SOLUTION ... well, it's quite simple. Take a look at your furniture and your clothing. Make sure you ALWAYS have a cotton garment between synthetic materials. Never let synthetics brush together. Polyester against nylon, for example, is asking for trouble.

As for WHY this strange situation has come about, it may be that you've bought a new nylon carpet (wear leather soled shoes or buy an anti-static treatment spray for the carpet). Or maybe your wife got a nice new dress or some other garment for Christmas. If you think about what has changed, you'll probably see one or two garments or furniture that play a major role in the problem.

Anti-static sprays can provide a short term solution (needs to be repeated periodically) but the best answer is to remove the offending articles or cover them with cotton fabric.

Electric shock when leaving a vehicle

The same principle applies as above. If you wear synthetic clothing this will brush against other synthetic clothing and/or the synthetic seat cover. Your body will acquire a high voltage electric charge which will be released when you step out of the vehicle and then reach out towards the door.

The shock that you feel is the arc of electricity that ocurs just before you touch the door. However, if you take a tight grip of the door or car body metalwork before and during the time when your feet touch the ground, you will often discharge the voltage without feeling it. But cotton clothing and seat covers are the best solution.

Electric shock from Dyson Vacuum Cleaner

I was on your static electricity site, and I have a question. We bought a Dyson vacuum cleaner in June, and I get a 'huge' shock when vacuuming certain rooms in the house. I have contacted Dyson and they have advised me to use moisturiser, use antistatic cloths on the vacuum cleaner etc. Is there anything that you suggest I can do to the vacuum cleaner to make it more "user friendly" like earth it somehow? Would it help to wear rubber gloves?

What you say on your website makes a whole lot of sense, and it does occur when the weather warms up and the air is drier - but I have become real scared of the vacuum cleaner, and have never experienced this before using Dyson.

Hoping you can help in some way.

regards, Judy

Vacuum cleaners that are constructed in non-conductive plastic work very much like a Van de Graaf generator. The dust holds a static charge and, when it is swirled round, the charge can be transferred to the casing and the hose of the vacuum cleaner. Add to this the friction of the brushes on a nylon carpet, the friction of the flexible hose sections against each other, and the movement of the machine across the carpet and you have an excellent static charge generator.

I have experienced the same, and for what it's worth it is only static electricity, not mains !. Earthing doesn't usually help, unfortunately. But I have heard good results from people who have used "Bounce" or any other Fabric Softener sheet to wipe the hose, handle and wand. You may find that using rubber gloves helps or wrapping the handle with our self-amagamating tape. Failing all else, hire a maid ! :)

Mark

 

Copyright ©1999 Martin Pickering
Version 1.1 updated on February 27, 2006
This file may be downloaded for private and personal use but NO part of it may be published in any form without the prior permission of the author.

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