Setting Up an ESD Mat

[Tyrian]

Hi all,

I've recently set up my own electronics lab, only to realize that I have a significant problem with static electricity.  I've read through the EEVBlog thread here and this site here to get some more information.  From that, I picked this mat from Newark/Element14, but have yet to order it.

My real question is on setup.  All of my lab equipment is run off a single, large APC surge protector.  When I set it up, I know it should be wrist strap -> mat -> earth ground.  The question is how do I terminate the mat to earth?  Can I terminate to the surge protector (most convenient) or should I terminate to the outlet itself (difficult to get to)?  Is it sufficient to hack off a power plug and splice the earth ground to the mat lead or it there some special method that should be used?

Thanks!

[gilbenl]

IMHO...After checking that you have a good ground connection in your home, connecting the lead from the ESD mat to the center screw on an outlet should suffice. Please don't just go putting it on that center screw without properly checking the voltage between neutral and ground.

http://www.esdmat.com/How_to_install_ESD_Workstation.php

[rdl]

If the surge protector has a 3 prong grounded plug, then all its outlets should be grounded too. You probably should check for continuity just to be sure.

The way I did mine is kind of crude. I just took a 1 inch long screw that was about the right diameter and kind of screwed it into one of the ground holes on an outlet, then attached the alligator clip (from the cable on the ESD mat) to the head of that screw.

[Tyrian]

What about cutting off the lug of the mat -> earth ground cable, splicing a banana jack on instead, and then sticking the banana in the earth ground hole?  I'd just need to make sure I didn't cut off the 1MOhm resistor in the cable.  If it's unavoidable, then I can just splice in a new resistor between the cable and the banana jack.  I have a bunch of 5% tolerance 1MOhm resistors on hand. 

[nanofrog]

From that, I picked this mat from Newark/Element14, but have yet to order it.

If you don't mind grey, then you might want to take a look here (less than half the price; also 24"x48" but a bit thicker @ .080" instead of .065"). They have other sizes as well in what's left of the closeout mats if you you're a bit flexible on size (although nice, you don't *need* to cover the entire desktop; just a sufficient working area).

What about cutting off the lug of the mat -> earth ground cable, splicing a banana jack on instead, and then sticking the banana in the earth ground hole?  I'd just need to make sure I didn't cut off the 1MOhm resistor in the cable.  If it's unavoidable, then I can just splice in a new resistor between the cable and the banana jack.  I have a bunch of 5% tolerance 1MOhm resistors on hand.

It would work, but be careful not to kick it out of the receptacle. Really would be better if you can place the ring terminal beneath a grounded screw (may be one on the APC unit; also make sure you get through any paint on them).

[Kjelt]

Don't connect the mat directly to protective earth. It is supposed to be connected through a 1Mohm safety resistor, or better three 330k safety resistors. These should be more than just mains voltage (think 600V), a half or one watt types I believe.
Ask free_electron he knows exactly which parts.
Reason you don't want a hard earth bonding pointing at your mat is safety.

[GreyWoolfe]

What about cutting off the lug of the mat -> earth ground cable, splicing a banana jack on instead, and then sticking the banana in the earth ground hole?  I'd just need to make sure I didn't cut off the 1MOhm resistor in the cable.  If it's unavoidable, then I can just splice in a new resistor between the cable and the banana jack.  I have a bunch of 5% tolerance 1MOhm resistors on hand.

My solution was to get a 3 prong plug from Home Depot and remove the hot and neutral pins.  The one I bought has a rubber boot on it so I fitted a small banana jack wired to the ground pin and plugged the ground wire into it.  It stays fine in the outlet without the other tabs.  No cutting or anything.

Edit:  I forgot to mention that my common ground point came with a banana plug on it which is why I took the route I did.

[Tyrian]

@nanofrog -- I had to use a gray mat at work once.  I kept losing parts on it.  Plus, I googled for the detailed datasheet and couldn't find one.  Thanks for the link, though.  I'll keep it in my back pocket, in case of emergency.

@Kjelt -- I'll PM free_electron if I have to do any cable modding.

@GreyWoolfe -- I like that idea.  I might use that to terminate.

I think that's it for any questions then.  Time to go test my outlet!

[G7PSK]

You should use a proper grounding plug, like one these, many mats are supplied with one.

http://www.ebay.com/itm/USA-Anti-Static-ESD-Grounding-Earth-Bonding-Plug-1-x-10mm-stud-/380842410498?pt=LH_DefaultDomain_3&hash=item58abfa0202

[nanofrog]

@nanofrog -- I had to use a gray mat at work once.  I kept losing parts on it.  Plus, I googled for the detailed datasheet and couldn't find one.  Thanks for the link, though.  I'll keep it in my back pocket, in case of emergency.

They have others (different sizes & colors, but may still be usable). Main point was, you can get a good mat for less than the one you linked here in the US if you know where to go and can be a little patient.

Sale and clearance items can be worth your time browsing, and there's also a seller on eBay (located in Canada) that has decent prices if there isn't a sale/closeout offering that will suit your needs. So there's no need to pay $87 for a mat.

[xwarp]

You can't run the mat ground to the work bench?

[Neganur]

What about floor mats?

From what I can tell I would want to buy either conductive ones (10E3-10E8 Ohm) or the sandwiched conductive/dissipative (bottom 10E5, top 10E8) and connect them with e.g. Multicomp grounding cords (no resistor) to the earth bonding point (which has resistors).

The earth bonding point supplies several 10mm studs via 1 MOhm 1 W resistors and usually a 4mm banana plug socket (without resistor) and is connected directly to EPA ground.

How effective are purely dissipative floor mats? If I only have one stud in a corner of the mat connected to a grounding point through a 1MOhm resistor cord I could imagine that the charge dissipates slower than if the mat had the conductive bottom layer and a direct connection (without resistor) to the earth bonding point. I mean, why would you have a conductive bottom and then put a resistor in series when the top layer of the mat already is highly resistive?

Also, it's important to distinguish between systems that have their own earth connection (i.e. not via a wall outlet) and those that plug into the wall outlet. The outlet style earth seems to be the most common one in private homes. At work, we have a separate grounding point for ESD directly from the switch board, no resistors until you attach an earth bonding point at your work station and also no need to be afraid that your wall outlet puts live potential on the wire.

Soldering iron ground connector directly to EPA earth or via 1 MOhm bonding point btw?

[jlmoon]

Okay, how about a count of the number of users on here that have a Halo grounding ring system in their home lab.  To which the Floor and workspace mats are attached.

[KJDS]

How effective are purely dissipative floor mats? If I only have one stud in a corner of the mat connected to a grounding point through a 1MOhm resistor cord I could imagine that the charge dissipates slower than if the mat had the conductive bottom layer and a direct connection (without resistor) to the earth bonding point. I mean, why would you have a conductive bottom and then put a resistor in series when the top layer of the mat already is highly resistive?

Don't think of them as high value resistors, they more closely resemble a high voltage zener, high impedance to low voltage but low impedance to high voltage.

[G7PSK]

I think the resistor is to limit current through you if you touch something live and the earthed mat or are wearing an ESD wrist band.

[Neganur]

Aye no doubt about the need for wrist band resistor since its contact resistance is supposed to be less than 160 Ohm. I was purely wondering about the mats, which are not conductive enough to cause any problems when you touch mains. 1 MOhm more or less will make little difference in that case.
But the comment about high voltage behaviour (which is exactly what the mats are supposed to remove) made me wonder how quickly they are supposed to remove static charge. Gotta get my hands  on those standards.

[kingofkya]

A pc or other chassie screw also works good in a pinch. As long as there little chance it will be unpluged.


Also have good bought qute a  few ESD mats from this guy there farly nice quality and the connector they come with already has the 1mohm resistor in the cable. There significantly cheaper than digkey or mouser when i looked last
http://www.ebay.com/usr/canvu0_0?_trksid=p2047675.l2559

[nanofrog]

I was purely wondering about the mats, which are not conductive enough to cause any problems when you touch mains.

Top layer, sure, as it's in the 10^8 Ohm range. But do keep in mind that the bottom conductive layer is only in the 10^5 Ohm range. Quick measurement on one of mine indicates ~20k, so a 1M in the ground cord is actually a good idea (technically, the resistor is optional, but usually present IME).

And it seems that most kits come with a 1M resistive cable (black wire = 1M resistor; green w/ yellow stripe = no resistor).

NASA's MSFC-RQMT-2918 document may be of some interest (direct .pdf link).

But the comment about high voltage behaviour (which is exactly what the mats are supposed to remove) made me wonder how quickly they are supposed to remove static charge. Gotta get my hands  on those standards.

If I understand what you're looking for, http://www.esdjournal.com/techpapr/ryne/rynedisc.htm gives you those specs.

Worst case Human Body Model (HBM), is a discharge of 6.2mJ, and the discharge rate cannot go below 2.01ms. Anything faster than that, and you get an ESD event.

Hope this helps. 

Also have good bought qute a  few ESD mats from this guy there farly nice quality and the connector they come with already has the 1mohm resistor in the cable. There significantly cheaper than digkey or mouser when i looked last
http://www.ebay.com/usr/canvu0_0?_trksid=p2047675.l2559

I've bought from this seller as well. Good quality mat at decent prices. 

Only time I've beaten his pricing, was with a closeout mat from all-spec (got one hell of a deal this way; paid ~ 35 - 40% of retail IIRC).