What do I connect wrist strap to?

[insight]

Hi,

I am quite a rookie, so please do not laugh.

Is it enough to connect the wrist strap just to any handy metal object, like 30cm metal ruler, or does it need to be something chunky, like central heating radiator?

How do I remove electrostatic charge from my clothes?

regards, dejan

 

[JimB]

The wrist strap should be connected to earth.

So, if the C/H radiator is earthed, connect to that.
You could connect it to the earth pin of the mains outlet on your workbench, there are dummy mains plugs available which just have the earth pin and a connection for the wrist strap.

When I am at my own workbench, I connect the wrist strap to a 4mm earth terminal on my spectrum analyser, because it is a convenient point and it is earthed via the S/A mains lead.

As for removing static from clothes, I dont know, other than wearing cotton clothes which dont have synthetic fibres.

JimB

 

[ericgibbs]

Hi,

I am quite a rookie, so please do not laugh.

Is it enough to connect the wrist strap just to any handy metal object, like 30cm metal ruler, or does it need to be something chunky, like central heating radiator?

How do I remove electrostatic charge from my clothes?

regards, dejan

Hi,
If its a commercial or homemade earthing wrist it MUST have a high value resistor in the lead going to the earthing point.
A 470K or 1M0 would be OK, without the resistor, if you come into contact with a live wire you could receive a serious electrical shock, the resistor reduces the current to a safe level.

If you have the luxury of carpets near your work station, walking on synthetic fibre carpets can build up a strong electrostatic field on your body. You can buy aerosol sprays for carpets to reduce static.

A method I use is to have a strip of aluminium foil wrapped around the soldering iron handle, this strip is earthed via a 470K resistor.
So every time I use my iron I get rid of any ESD risk.

Another simple method is to get a poylstyrene ceiling tile, wrap it both sides with alum kitchen foil, earth it with a wire and resistor.
Place all the ESD sensitive devices on the foil covered tile. Every time you pick up a component you are earthed.

With care you can push the legs of ic's and transistors thru the foil, so all the legs/pins are shorted.

Hope this helps.

 

[Speakerguy]

I have never worn a wrist strap and I've never had an ESD problem. I would only worry about it if you are in a particularly dry area or have static problems you already know about (frequently shocked by door knobs or cars for ex.).

 

[insight]

- Can earth, for ESD purposes, be any large metal piece on its own, or that large metal piece needs always to be connected to the ground of the mains wall socket?

- Is there a way to test weather my C/H radiator is earthed?

cheers, dejan

 

[JimB]

- Can earth, for ESD purposes, be any large metal piece on its own,

No, how do you know whether the "large piece of metal" is not charged itself.

or that large metal piece needs always to be connected to the ground of the mains wall socket?

Yes.

- Is there a way to test weather my C/H radiator is earthed?

Use a multimeter set to the low ohms range, and measure the resistance between the radiator and a point you know to be earthed.

JimB

 

[ericgibbs]

I have never worn a wrist strap and I've never had an ESD problem. I would only worry about it if you are in a particularly dry area or have static problems you already know about (frequently shocked by door knobs or cars for ex.).

hi Spkrguy,

Dry areas are the worst areas for a ES build up, especially dry frosty weather.

The ESD can damage a semiconductor, either destroy it, shorten its life or change its voltage thresholds,
even if you are not aware of any discharge taking place.

Always observe the manufacturers recommendations regarding ESD.

 

[Rolf]

Soldering Iron Handle Modification .........

{snip}
A method I use is to have a strip of aluminium foil wrapped around the soldering iron handle, this strip is earthed via a 470K resistor.
So every time I use my iron I get rid of any EDS risk.
{snip} QUOTE]

Eric, I really like your suggestion, it prompted me to modify my Weller like this.
https://www.pbase.com/sinoline/image/89894276
I used adhesive copper foil, used for making stained glass, and a resistor installed like in the picture.

 

[David Bridgen]

- Can earth, for ESD purposes, be any large metal piece on its own, or that large metal piece needs always to be connected to the ground of the mains wall socket?

The purpose of the wrist strap is to ensure that there is no potential difference between you and the surface upon which the sensitive parts sit.

As long as that is done, as long as the person is connected to the surface, it doesn't matter whether that connection is made through the Earth or not. Earth is irrelevant.

cheers

Your good health.

 

[Rolf]

If this is correct .....

The purpose of the wrist strap is to ensure that there is no potential difference between you and the surface upon which the sensitive parts sit.

As long as that is done, as long as the person is connected to the surface, it doesn't matter whether that connection is made through the Earth or not. Earth is irrelevant.

Your good health.

Then what happens to this voltage sensitive part, charged to a high static voltage, when you touch it with your soldering iron, that is grounded, like some of mine. Puff and it is gone!
I think keeping everything as close to earth potential as possible, is essential.

 

[David Bridgen]

Then what happens to this voltage sensitive part, charged to a high static voltage, when you touch it with your soldering iron, that is grounded, like some of mine. Puff and it is gone!
I think keeping everything as close to earth potential as possible, is essential.

Quite right.

My answer relates to the original question about a wrist strap, and still stands.

Once we bring test gear and tools into play that's different only insofar as they ARE, generally, connected to Earth.

I am trying to underline the fact that it's the common connection which is important, whether Earth is involved or not.

 

[ericgibbs]

hi Rolf,
Saw your iron image, you have made a better job of it than my version.

Hi David,
I cannot fully agree with your statement, ref relative 'earthing'.

All your bench and components maybe at a given potential, but you, after say, walking across a carpet, you will most likely be at a different potential to the bench etc...

If you pick up a bench component, a ESD current will flow between you and the component until the potential equalises.
This current could be enough to damage the ESD sensitive component.

I would agree with Rolf, consider 'earth' as being the common reference point.

Its such a minor precaution to take when handling ESD devices.

 

[David Bridgen]

Good morning Eric.

I agree, but I don't see how that negates what I have been saying.

 

[ericgibbs]

hi David,
Not trying to negate your post, just trying to re-enforce to the less experienced members the importance ESD damage prevention .

Spent about 3 years stationed in Linconshire. [RAF].. enjoyed my time there.

 

[Nigel Goodwin]

Spent about 3 years stationed in Linconshire. [RAF].. enjoyed my time there.

Didn't you miss the hills?

 

[ericgibbs]

Didn't you miss the hills?

Parts of it are quite 'hilly' others like a bowling green!

I expect you have tried the local brew 'Dragons Blood', my favourite tipple when I was younger.

 

[insight]

Thanks everybody for the explanation.

Just a bit more questions. I have connected the other end of the wrist strap to the ground on my power supply. So any ESD will go from myself to that ground etc.

Question is, what happens if that power supply fails internally and the live wire gets connected to the outside case. Would than live current go through myself?

cheers,
dejan

 

[Nigel Goodwin]

Thanks everybody for the explanation.

Just a bit more questions. I have connected the other end of the wrist strap to the ground on my power supply. So any ESD will go from myself to that ground etc.

Question is, what happens if that power supply fails internally and the live wire gets connected to the outside case. Would than live current go through myself?

As has already been said, you don't connect yourself via a piece of wire (you connect via a high value resistor) - and it would really be pretty silly to connect to a piece of equipment, you connect directly to an earth point. In the UK a common point is the earth pin on the UK 13A mains plug, and commercial wrist straps are available with connectors to plug in a 13A socket.

 

[ericgibbs]

hi insight.

>> Question is, what happens if that power supply fails internally and the live wire gets connected to the outside case. Would than live current go through myself?

The psu case/chassis should be grounded via the 3 core mains lead.
If not, I would add a 'earth' ground wire to the mains connector.

A point I would be aware of are mains bench lamps, quite often they are just two wires.
Due to heat of the lamp, the wires to lamp socket degrade and can touch the metal structure of the lamp,
especially if the lamp is swung around a lot.
Add an earth wire to the lamp structure if not already fitted.

I got a nasty shock a few years ago when my face touched a defective bench lamp.

 

[gaurav_sharma132]

Guys, it was great discussion. Helped alot. But I have query:

Like in my house I think my earth is not proper there is some leakage but I'm not sure. So can you please guide me how to test it. And if leakage is there how I should get rid of it.

Thanks and Regards