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View Full Version : need to know wire size from ground rod to anti static table mat.



allie
03-07-2010, 03:42 AM
·Hi all, I am setting up an anti static table mat to a ground rod that is 55 feet from the table. What size of a conductor should I use.

Allie
·

Mike Green
03-07-2010, 04:23 AM
Any single ground connection over a 55 foot distance is going to have problems with inductance and capacitance. The question is really how to set up an anti-static environment. What do you have in the immediate environment? Do you have any nearby source of electricity? Does that include grounds? Is your ground rod connected to anything else?

Really what you want to do is to dampen any local static electrical fields and discharges. Ideally all of the nearby work surfaces (and flooring) would have a high resistance conductive coating. Proper choice of materials (including paint) would address this. You can buy carpets and mats that tend to dissipate static charges. You could also increase the relative humidity in the nearby area.

You really have to look at your local (bench) electrical grounding system and its relationship to the earth ground since you could have a significant potential between any equipment grounds and the earth ground.

allie
03-07-2010, 08:32 AM
Just a hobbiest working at home. There is no heavy electrical equipment only 220 volt base board heater, LCD TV, satellite dish receiver,DVD player, and (2) 115 volt plug in's, one with a satellite dish power bar for TV equipment.
The floor just standard house hold floor tile. My work bench is just a piece of counter top. My seating is a small sofa.
The ground rod is one that use to be the main one, for the main electrical panel. The electrical panel was moved to a different location in the house and the electricans put in a new grounding rod and disconnected the old one. The old one has nothing connected to it now, so I thought it would be a good one for me to use for my anti static table mat.
The table mat that I,m buying is from electronic express the 3M series 2ft. x 4ft. I also have an anti static rist strap which I'll be hooking to this grounding system. Can I hook it to the common point where I hook the table mat so that I won't have to run another wire to the grounding rod.

bill190
03-07-2010, 09:24 AM
In general larger gauge wire has less resistance.

But·in your case you would need to be practical. Perhaps a stranded wire which was larger, yet still flexible so you could easily move your anti-static mat out of the way so you could work on something else. And I would attach the wrist strap to the same ground wire as the mat.

As to grounding,·some things can have multiple VERY large·conductors like these...

http://www.alcoltd.com/copper-braid-pages/main-product.htm

http://www.spokanehams.com/repeaterphotos_TX.htm

stamptrol
03-07-2010, 07:49 PM
A secondary point is that you describe the case where you have two separated ground rods. That is definitely not the way to go as two separated ground rods can be subjected to significant potential difference during fault conditions. The concept is to have a single, very good, ground point in the system. If you are connecting your static mat to the old ground rod, at a minimum it needs to be tied to the new one as well.

For your purposes, a high resistance connection from your static mat and wrist strap to the ground connection of a nearby electrical outlet will suffice. And, make sure you know that the outlet was properly grounded!

Cheers,

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Tom Sisk

http://www.siskconsult.com
·

allie
03-08-2010, 12:27 AM
Thanks all, for your reply's.

Allie

allie
06-12-2010, 06:24 AM
Stamptrol
I had the ground rod wired to my table but I had to move to a different province for work reasons,so now I want to go the way you said using the ground connection of a near by electrical outlet. The high resistance you mentioned is already in the wrist strap(1 or 10 meg ohm), or do I need more higher resistance. Would this be alright for the wrist strap? As far as the table matt goes it is 3M's (approx $100 range) good quality with a y connector for the mat and two banana jacks for wrists straps. Does the table matt connector need more high resistance added and how much. I'm also thinking of adding a ground fault circuit interrupter (same as bathroom recepticals for electric razors and hair dryers, then I hook to the ground circuit on this if it doesn't trip all the time when I hook the table matt and my wrist strap to it. This will give me some extra protection in case something in the household circuits shorts, or at least I think it should. You never can be to safe with a wrist strap on.

allie

Post Edited (allie) : 6/11/2010 11:37:24 PM GMT

allie
06-13-2010, 08:33 AM
Hi all, I hooked up the ground fault circuit interrupter to a plug, so that I can plug it in to any standard household electrical circuit. Then I put a 10 megohm resistor from the ground terminal of the GFCI to the connecting cable going to my table matt and wrist strap = 11 megohm resistance with the matts and wrist straps resistance of 1 meg each.
Question; will this extra resistance of 11 megohms stop the anti static table matt and wrist strap from functioning properly or should I go for a lower resistance value from ground to connecting cable? I have the following values of 2.2, 3.3, 4.7, 5.6, 6.8, 8.2 all megohm range.
I did an ohms law calculation on the current which might come back through the ground if something on the electrical circuit faults = I=E/R. 120 volts / 11,000,000 ohms = .000.010.9 = 11 micro amps. Also I have the GFCI for extra protection.
Is this a safe way to have my grounding for myself and the tablematt.
I tested the above with the 10 meg resistor hooked to wrist strap and matt and the GFCI did not trip all seems o.k.
allie

Phil Pilgrim (PhiPi)
06-13-2010, 09:00 AM
Why bother with an earth ground at all? It's not necessary. The important thing is that you and the items on the mat be at the same potential. This is easily handled by the wrist strap and the wire that connects it to the mat. That's all you need.

-Phil

allie
06-13-2010, 09:18 AM
Thanks for your reply.
I did not know that, things which I read and my understanding of it is that a ground connection is needed to blead static electricy from me before I touch static sentitive devices. If I have a high static charge on me how will it be discharged without a ground?

allie

Phil Pilgrim (PhiPi)
06-13-2010, 10:06 AM
allie said...
...ground connection is needed to blead static electricy from me before I touch static sentitive devices.

But, if the parts are not also at ground potential, you will still get a discharge. The main thing is that you and the parts be at the same potential, whether it's "ground" or something else.


allie said...
If I have a high static charge on me how will it be discharged without a ground?

With your wrist strap on and its cable snapped to the mat, you can handle the parts sitting on it, since you will be at their potential (i.e. they will be at yours).

-Phil

Forrest
06-13-2010, 07:55 PM
I disagree with Phil on this one. You need a ground wire connected to the mat/wrist strap for the energy to dissipate. I know - work requires me to go thru ESD training every year.

I agree with Stamptrol - a connection to a grounded outlet should suffice. However I don't know the proper hookup to a GFCI.

Phil Pilgrim (PhiPi)
06-14-2010, 03:17 AM
Forrest,

You may have a good point regarding charge dissipation, and I agree that connection to a properly grounded outlet should be adequate. (Test it first, of course.) I find it odd, though, that static dissipative mats (at least the one I have) come with only one snap connector, that being for the wrist strap. Consequently, I've never used mine with a ground.

-Phil

Forrest
06-14-2010, 04:14 AM
Phil,

On mat's with one spap, typically the ground wire is connected thru a snap connector, and the wrist cord is snapped on top of the ground snap. The snap connectors stack on-top of one another. The ESD energy will dissipate thru the mat and the wrist cord has a built-in 1 Meg resistor.

Forrest

PJ Allen
06-14-2010, 07:50 PM
This is not a Parallax Basic Stamp question at all.

Who is the moderator for this Forum anymore?· Is there one?

sumdawgy
06-14-2010, 08:10 PM
PJ Allen said...

http://forums.parallax.com/images/smilies/nono.gif·This is not a Parallax Basic Stamp question at all.

Who is the moderator for this Forum anymore?· Is there one?



Oh lighten up,·I'm perfectly happy with assuming the table is for a basic stamp project.·You're "legally" right that it's not a stamp question because he never said stamp.· But, all he/she had to say was that it was FOR·a stamp project and "legally" it would qualify.·· It dates back to march.·And the completed discussion makes sense to do.

It may even be(or have been)·usefull to someone else working a stamp project with a bad static mat setup.

(BTW... I'll UPS your shoes back!)http://forums.parallax.com/images/smilies/smilewinkgrin.gif

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Before you criticize someone, walk a mile in his shoes. That way if he gets angry, he'll be a mile away and barefoot. - unknown

allanlane5
06-14-2010, 10:29 PM
A couple of notes:

1. A simple 'zip-cord' connection of 20 Ga wire to a good ground would be sufficient. And for draining 'static charge' you don't need a lot of current, so that cord could be quite long.

2. A static mat with wrist-strap DOES have high-resistance (1 MegOhm or so) between the wrist strap and the mat. We're trying to drain static charges, not electrocute people.

3. So you probably want to maintain a high-resistance to ground (again, 1 MegOhm or so) in the line between the static mat and your ground. This will be
sufficient to bleed off static charges. A low-resistance path to ground can be a shock hazard, so you want to avoid that.

4. You really don't need your mat & wrist-strap combination to BE at some "global ground" -- having everything be at some "local ground" between the mat, your strap, and the
board you're working with is quite sufficient. What you're trying to avoid is having a few thousand volts of static charge (but with VERY low current) 'zap' an I/O pin when you
touch it -- having the mat, strap, and board all connected with 1 Meg-ohm resistance between them is sufficient for this.

skylight
06-15-2010, 03:19 AM
The situation where phil mentions the user and components are at the same potential is sound as without pd there is no current flow and no discharge, the problem that may occur is when you offer an alternative potential such as a grounded soldering iron perhaps?

allanlane5
06-15-2010, 03:44 AM
Okay, if you've got a "grounded soldering iron", then clearly you've got a "ground" nearby to plug it into, right?

And I'm assuming when you're soldering, the board you're soldering is NOT plugged into the wall.

The fact still is, you want a high-resistance connection (1 Megohm) between you and ground to protect yourself from accidents.

allie
06-15-2010, 08:58 AM
I can agree with PJ Allen, this probably sould have been started on the sandbox site, so in closing this thread I'd like to say thanks for all of the replys and mention that it is for a stamp project to be put together. I'll be using the bs2 and bs2p40 on this mat.

I always unplug my boards before I solder.

I have the GFCI already wired, no problem with that, as I took a one year electrical course and everything works fine. I even used one of those electrical tester lights with the 3 colour status lights to show that the neutral, ground and hot wires are in the right places.

Thanks again and now I'll close this thread unless some one wants me to move it to the sandbox.

allie