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Grounding Strap and Wall Outlet Ground

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Foolios

Member
Joined
May 9, 2006
I don't think I have many things in my room to ground to so I took a power cord and left only the ground plug on it.

Then I attached my wrist strap to the ground wire on the other end.

The funny thing is I found a green ground wire and a bare ground wire in the cord. I didn't know it had a bare ground wire in there as well. So I twisted that bare one around the green coated one.



2.jpg




I then checked for continuity from the ground prong of the power cord to the metal plate on my wrist strap and found that it's working as designed.



Now my question is, do you think that this is will work for keeping electronic components safe from static?



Are there any other safety issues with my using ground through the outlet like this?



Thanks so much in advance.
 

ratbuddy

Member
Joined
Aug 24, 2007
Maybe it's just me but I'd never wear anything plugged into a power outlet no matter which prongs were cut off :beer:
 

Theocnoob

Member
Joined
Dec 1, 2007
Location
Near Toronto Canada
Provided you have done this right you should be ok *though I take no responsibility for my comments*

most wrist straps include an attatchment to go into a ground socket.
 

larrymoencurly

Member
Joined
Jul 14, 2002
Put a 1 million ohm resistor in series, both for safety (in case the wall outlet is wired wrong or if you contact high voltage) and better ESR protection (resistor limits current, resulting in less damage to chips). Notice that all commercial anti-static wrist straps have a million ohms of resistance.
 
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Foolios

Member
Joined
May 9, 2006
Put a 1 million ohm resistor in series, both for safety (in case the wall outlet is wired wrong or if you contact high voltage) and better ESR protection (resistor limits current, resulting in less damage to chips). Notice that all commercial anti-static wrist straps have a million ohms of resistance.

Will that resistor be too high of a value? I'm just afraid that it won't allow the static to discharge from the body easily.

I could just splice the wire and solder the resistor into place.
 

cyberfish

Member
Joined
May 23, 2008
Location
London, England
If we think in terms of extremes, having a resistor of infinite resistance is equivalent to an open circuit, meaning it will act as if the cord is disconnected, which is obviously no good.

If, while wearing the strap, you touch some high voltage, your body and the cord will be in parallel. The way the strap protects you is that it provides an alternative path with lower resistance, so current will flow that way, instead of through your body. In this regard, no resistance is better, because almost all the current will flow through the cord, instead of through your body.

However, a lower resistance on the cord means a lower equivalent resistance for you + the cord. Therefore, if you touch the same voltage, more current will flow through your hand (then into the cord) than if you aren't wearing it. No current will flow through the rest of your body, though.

So it's probably a good idea to add a resistor, but it's not the bigger the better. It still has to be significantly lower than the equivalent resistance of your body.
 

cyberfish

Member
Joined
May 23, 2008
Location
London, England
BTW, soldering is no good for mechanical connections. I usually just tie the wires together and tape them, but I'm sure there are even better ways.
 

Bobnova

Senior Member
Joined
May 10, 2009
You wouldn't want to touch high voltage wearing a wrist strap of no resistance, all the electricity would flow through you to the strap, then through the strap. Expect gnarly burns on the wrist with the strap, and heart issues if it wasn't that arm that hit the HV.
Now if it was the strap that hit the HV, i agree completely.

The 1mega ohm resistor is mainly to protect you if you touch something you shouldn't i think. Can't think of anything else it'd be useful to.
I would put a resistor in there, at least 10k-ohm, 100k would be better, 1megaohm is what most use so that is probably what i would use.
You don't want to roast yourself, it's not fun. Plus it seems like the manufacturers probably have some grand plan with the megaohm resistor in there.
 

Audioaficionado

Sparkomatic Moderator
Joined
Apr 29, 2002
Will that resistor be too high of a value? I'm just afraid that it won't allow the static to discharge from the body easily.

I could just splice the wire and solder the resistor into place.
1 meg-ohm is just right. I worked for a high-end audio company (Taralabs) and the idiot electrician swapped the green wire with the black wire on a work bench. The assembly tech complained of a slight electrical tingling sensation when ever he contacted the metal tip of his solder iron to a metal chassis he was working on. Turns out that supposedly earth grounded tip was floating at 120 VAC. Good thing it was 120 VAC through over 1 meg-ohm of resistance.

An ESD charge doesn't have very much capacitance or current so it can be very quickly drained off with even 1 meg-ohm of resistance. As long as your plug is wired correctly, you should be good to go. Also be careful not to wear static prone clothing like polyester. I used to take off my shirts (sparkling as I pulled them over my head) at night and put them on metal TV trays with plastic prongs insulating them from the floor. I could pull a quarter inch spark off the tray to my finger. Ouch!

Most ESD events that damage chips can't even be felt and often don't even need direct contact to damage nearby sensitive ICs. Some times the damage doesn't even show until some time later. Days or weeks.

Most wrist strap leads have meg-ohm resistance built into them.
 

Bobnova

Senior Member
Joined
May 10, 2009
1 meg-ohm is just right. I worked for a high-end audio company (Taralabs) and the idiot electrician swapped the green wire with the black wire on a work bench. The assembly tech complained of a slight electrical tingling sensation when ever he contacted the metal tip of his solder iron to a metal chassis he was working on. Turns out that supposedly earth grounded tip was floating at 120 VAC.

I've felt that tingle, plus a little bit of muscle jumping in my arm. Good thing to watch out for!
 

Mpegger

Member
Joined
Nov 28, 2001
An easier method (if working on computers) is to plug in the normal PSU power plug to a properly grounded switched outlet (or switched power strip), and use the switched outlet to turn off the power. The ground should still be active if its properly wired, regardless of whether the power is on or not. Then just clip the ESD strap to a bare metal portion of your case.
 

Bobnova

Senior Member
Joined
May 10, 2009
That's what i usually do, though some PSUs don't have a switch on them, they're always live if they are plugged into the wall. Pretty stupid if you ask me, but nobody did i guess :p
 

Mpegger

Member
Joined
Nov 28, 2001
That's what i usually do, though some PSUs don't have a switch on them, they're always live if they are plugged into the wall. Pretty stupid if you ask me, but nobody did i guess :p
Hence why I said plugging the PSU into a switched outlet or switched powerstrip. :beer:

If the PSU has a switch, you just simply plug it into any regular outlet, switched or not.
 
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Foolios

Member
Joined
May 9, 2006
Sounds great, use the power strip as the shut off mechanism for the computer. And also still give the computer a ground without having to be on.
Excellent idea.

Just be sure to check for continuity from the frame of the pc to the grounded outlet. So you know that the ground on the power strip is still passing through even when it's in the off position. More than likely I believe we would all think so.
 

Bobnova

Senior Member
Joined
May 10, 2009
Hence why I said plugging the PSU into a switched outlet or switched powerstrip. :beer:

If the PSU has a switch, you just simply plug it into any regular outlet, switched or not.

I had confusion, never seen an outlet with a switch. Forgot about the UK people (i guess every outlet has a switch on it) and outlets wired to light switches.
 
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Foolios

Member
Joined
May 9, 2006
LOL @ ESD strap . Cant tell you how many times I have worked on a PC on the carpet floor

And I am wondering how often you get BSOD and other errors in the systems you work on...

I have read quite a few posts on the subject. I have asked about the value of ESD straps from circuit builders, component makers, memory manufacturers and technicians.
Not one of them will tell you that ESD isn't a concern.
It's something you can't see and it's something that may not trouble you immediately.

But will possibly affect the user of it in the future.
How many times I heard a DIY say; Well geez, it ran fine when I had it. Must be something YOU did to it!
 

Audioaficionado

Sparkomatic Moderator
Joined
Apr 29, 2002
A lot of people don't worry about ESD and throw caution to the wind. They have their favorite safety net. :thup:

"What? Me worry?" "I'll just RMA it if it breaks and make everyone else pay for it with increased prices." :rolleyes:
 

larrymoencurly

Member
Joined
Jul 14, 2002
larrymoencurly said:
Put a 1 million ohm resistor in series, both for safety (in case the wall outlet is wired wrong or if you contact high voltage) and better ESR protection
Will that resistor be too high of a value? I'm just afraid that it won't allow the static to discharge from the body easily.
Considering that pink anti-static bubble wrap has something like a billion ohms a square cm or inch and is approved for anti-static protection, a million ohms isn't excessive.

Some electronics factories make workers pass through checkpoints where they have to plug in their anti-static wrist straps, and any that measure below 1 megaohms or above about 2 megaohms prevent the wear from entering the assembly area.
 

larrymoencurly

Member
Joined
Jul 14, 2002
An easier method (if working on computers) is to plug in the normal PSU power plug to a properly grounded switched outlet (or switched power strip), and use the switched outlet to turn off the power. The ground should still be active if its properly wired, regardless of whether the power is on or not. Then just clip the ESD strap to a bare metal portion of your case.
Wouldn't it be safer to disconnect the power plug from the outlet and connect the anti-ESD strap's clip to the AC cord's ground prong?