Grounding with anti-static wrist bands

[matthew6]

Hi all,

I'm a newbie, and have read in a "For Dummies" book that to properly ground oneself to work on electronics projects, one needs to run a wire from a cold water pipe to one's workspace to attach the wrist strap to.

This won't be very easy in my case, and I'm wondering about other options:

1. Can I just clip the wrist strap to the metal case of an appliance (e.g. computer) that is plugged in to a grounded outlet?
I'm in the United States (NM), in case that matters...

2. Alternatively, can I take a child safety outlet cover and drill a hole in it where the ground should be, place a wire through it, and run that wire to my workspace to attach to the wriststrap, or is this a crazy and dangerous thing to do?

3. I have a nearby coaxial cable outlet (in use): Is there someway I can creatively ground myself this way?

Thanks!
-Matt

 

[Optikon]

Hi all,

I'm a newbie, and have read in a "For Dummies" book that to properly ground oneself to work on electronics projects, one needs to run a wire from a cold water pipe to one's workspace to attach the wrist strap to.

This won't be very easy in my case, and I'm wondering about other options:

1. Can I just clip the wrist strap to the metal case of an appliance (e.g. computer) that is plugged in to a grounded outlet?
I'm in the United States (NM), in case that matters...

2. Alternatively, can I take a child safety outlet cover and drill a hole in it where the ground should be, place a wire through it, and run that wire to my workspace to attach to the wriststrap, or is this a crazy and dangerous thing to do?

3. I have a nearby coaxial cable outlet (in use): Is there someway I can creatively ground myself this way?

Thanks!
-Matt

You can do what you are suggesting. All you need is a good earth ground to bleed off charge so that you do not ESD the electronics that you will be handling.

For most electronics handling, having some humidity in the room and just briefly touching something grounded before handling works just fine. The most sensitive devices to watch out for are small geometry CMOS devices. I dont bother with ESD protection on a daily basis and I have never conclusively zapped something. But the theory is sound.

 

[phalanx]

Another option is to go to a hardware store and buy a NEMA 15-5 plug (standard 3 prong 120VAC 15A appliance plug), and only wire the ground contact. You then have a portable ground connection that is as close by as your nearest outlet.

As a HUGE word of caution, I always check the outlet first with one of those inexpensive plug-in testers with 3 lights. While I'm concerned about having a proper ground, I'm even more concerned about an incorrectly wired outlet that has the hot and ground wires switched! It does happen sometimes and it only takes 2 seconds to test the outlet.

 

[ljcox]

I just clip my wrist strap on to a screw in my magnifying lamp. The frame of the lamp is earthed via the power outlet.

 

[Zed]

In my experience it is Mosfet transistors that are most susceptible to static damage and as far as buffered 4000 series CMOS are concerned I've handled 1000s over the years without taking any static precautions and had no trouble at all.
When I do handle sensitive or expensive components I just touch a known good earth like the exposed metal of an earthed electrical appliance that is plugged into the mains.

 

[kchriste]

1. Can I just clip the wrist strap to the metal case of an appliance (e.g. computer) that is plugged in to a grounded outlet?

Yes, but make sure that there is a 1Mhm: resistor in series with the wrist strap wire. This will help prevent your death if you grab a live wire/appliance while wearing the wrist strap. Most wrist straps have this resistor built in but it is best to check with an ohm meter just to be sure.

 

[matthew6]

Thanks!

Thanks for the tips and cautions. Looks like I may not need the thing for most of what I do starting off, but I think I'll go with the clipping to a grounded appliance option when it seems prudent.

Two more questions though,

1) for kchristie (or anyone who can answer it). How exactly does the 1M ohm resistor function to save you from getting zapped?

2) Is there an easy way to test to see if you have a "good" ground? After a bit of searching, I've seen that sometimes 3-prong outlets aren't even really grounded.

 

[kchriste]

1) for kchristie (or anyone who can answer it). How exactly does the 1M ohm resistor function to save you from getting zapped?

It will limit the current through your body to a safe level. It is the high current though your heart that stops it. For instance, the spark you see in the winter after walking across the carpet is 10's of thousands of volts but has very little current behind it. But you can be killed by the 110/220V in your house wiring because it can supply alot of current especially if you are wet and in the tub and your wife tosses in a plugged in hair dryer.

2) Is there an easy way to test to see if you have a "good" ground? After a bit of searching, I've seen that sometimes 3-prong outlets aren't even really grounded.

There's no easy way. I guess you could take an ohm meter reading between the suspect ground and say a copper water pipe. That will just tell you that they are both connected together, but doesn't guarantee that they are grounded. If you can find the ground stake for your building, and trace it back to the pipe/ground only then can you be 100% sure.

 

[ericgibbs]

hi mathew,

When you have found an earth ground and proved it, using one of the methods already posted,
it would be advisable to ground all the test gear on your work bench.
Including the bench lamp,if you use one and the soldering iron.

As already stated you MUST have a high value resistor to ground from your wrist strap, 1Mhm: is OK.

>> 3. I have a nearby coaxial cable outlet (in use): Is there someway I can creatively ground myself this way? That would NOT be safe.

A method I use to protect my ESD [electrostatic sensitive devices] is to use a square piece of polystyrene,
[ a ceiling tile or a sheet from a transit case].

Wrap it all around with a sheet of aluminium kitchen foil, connect it to ground thru a 1Mhm: resistor,
then place your devices on the top of the foil.

If required you can press the ic or transistor thru the foil, the foil will short all the pins together and also keep them tidy.

Then every time you pick up a device you will automatically ground yourself.

I have used this method for many years and I don't get failures due to static discharge.

 

[Ambient]

Just be sure you remember to take the device off the foil before you run any power to it.

 

[ericgibbs]

hi ambient,

>> Just be sure you remember to take the device off the foil before you run any power to it.

The device refers to the individual semiconductor ic's, so there is no way you could power up the devices while they are resting on the foil.

Its not the pcb that you are working on thats on the foil, its the ready to build components.