My esd mat is trying to kill me - Page 1
Forum section: electronics / beginners

author: slim
author_rank: Contributor
timestamp: March 28, 2015, 05:04:07 pm
content: Had a few people wanting me to fix their PS3 and laptops.I worried about esd so I got one of these.http://www.amazon.com/gp/product/B009WU8J9I/ref=oh_aui_detailpage_o06_s01?ie=UTF8&psc=1I have a two wire system in my house so I "grounded" the mat to a multi outlet strip housing. I opened the strip and there is no connection to the housing.After fixing the ps3's and laptop I decided to do some soldering on a old tube amplifier and then test it out.I was about to plug it in on top of my new shinny mat and then I got to thinking... maybe not such a good idea.I mean hey, working on powered electronics on top of a rubber mat seems fine, but ain't these mats conductive?I measured the ohms between snaps on either end of the mat and it reads 50K ohms. with the wrist plug in thing attached to one of the snaps it reads 1M ohmsSo I assume that working on powered devices on a esd mat isnt a good thing.Also I have a hot air rework/solder station and noticed that my solder tip is tied to the grounding pin of the plug. being I dont have a grounded outlet should I plug this station into one of my outlets that is grounded to a rod outside?Any thoughts?Thanks

author: Rog520
author_rank: Regular Contributor
timestamp: March 28, 2015, 05:16:35 pm
content: I would set up a properly grounded electrical distribution, not only for ESD purposes, but also for your safety. 50kohms seems awfully low. Mohms seems more typical. With a resistance of megohms they are perfectly safe to work on.

author: edpalmer42
author_rank: Super Contributor
timestamp: March 28, 2015, 05:36:08 pm
content: The measurement between the snaps is misleading. Note that the description says that the mat is made up of a blue static dissipative layer and a black conductive layer. The dissipative layer has a resistance so high it's very hard to measure. That's what you're putting your equipment on so it should be fine. The black layer on the bottom is giving you the 50K reading.You, the mat, and the soldering station should be connected to the outlet that's grounded to the rod outside. An ungrounded soldering iron tip can build up enough charge to damage or kill a sensitive device. The wrist strap and the mat should have a 1 Mohm resistor in series with the ground lead so that if you touch a live circuit, the current through you will be limited to a safe value while still providing a path to bleed off the static charge. That's why the mat has two snaps - one for the mat's ground lead and one for your wrist strap. That gives you 2 Mohms from your wrist strap to ground, but that doesn't matter.Ed

author: slim
author_rank: Contributor
timestamp: March 28, 2015, 05:50:58 pm
content: Quote from: Rog520 on March 28, 2015, 05:16:35 pmThanks for the reply,My house was built in the 60's so there is two wire through out the house. in the converted room I use for this stuff I have a few outlets that I have box grounded to a few 10' rods outside.its the best I can do at this time. I have my oscilloscope hooked to one and my ham stuff to another.As far as the mat goes, it has a black part that snaps onto one of the snaps of the mat. this has banana jacks to hook a wrist strap into and a wire to hook to the ground of a outlet.being I dont have any grounded plug at that location I hooked it to the outside of a metal 4' 10 outlet bar at the bench.If i remove the black thing from the snap and measure ohms between the snaps I get around 51K ohms if I resnap the black part to the mat and measure between the other snap and on of the jacks that a wrist strap plugs into I get 1M ohms. I assume there is a one meg resistor in the black housing.The mat is two sided, a black bottom layer and a blue top layer. the metal snaps go thru both layers.So Is the mat defective as it reads low ohms? or is it because the snaps short both layers?

author: slim
author_rank: Contributor
timestamp: March 28, 2015, 05:53:09 pm
content: Quote from: edpalmer42 on March 28, 2015, 05:36:08 pmThanks for the replyI get it now.And just for the record, when I am working on the live chassis's I dont want to be grounded so I dont wear a wrist strap, I just wanted to be sure it was a good idea to have the grounded black part connected when doing live voltage stuff on the mat. I want to try to keep the chassis floating if you know what I mean.Thanks again

author: slim
author_rank: Contributor
timestamp: March 28, 2015, 06:15:08 pm
content: Well I have spooked myself now.I guess I will use the mat for esd stuff and then roll it up and just work on the wooden tabletop when working on the live stuff.

author: helius
author_rank: Super Contributor
timestamp: March 28, 2015, 06:24:25 pm
content: The chassis is either live or floating, pick one.

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: March 28, 2015, 10:17:22 pm
content: Quote from: slim on March 28, 2015, 06:15:08 pmIn my experience the wrist strap is far more effective and critical in avoiding ESD than the mat. I didn't like wearing it at first but you get accustomed to it after time.With a dissipative resister of course.

author: edpalmer42
author_rank: Super Contributor
timestamp: March 29, 2015, 04:59:49 am
content: Wear the grounded wrist strap all the time. Use the grounded mat all the time. The 1 Mohm resistors make it perfectly safe to use them on live equipment. Also, the blue static dissipative layer means that the live equipment won't know or care about the black conductive layer underneath.If you don't wear the wrist strap you can zap equipment that's turned on just like you can zap equipment that's turned off.Ed

author: Chipmunk
author_rank: Contributor
timestamp: March 31, 2015, 09:26:58 am
content: I'd have a look at your main panel, even back in the 60s the neutral SHOULD be grounded at the service entrance (your profile flag shows you to be from the US)Your solution of ground rods outside seems to be a pretty good one from the ESD point of view. I'd install GFCI outlets too (or get an electrician to do so!). They're quite happy to work without the ground wire present and will provide you a little more safety

author: jlmoon
author_rank: Unknown
timestamp: March 31, 2015, 02:21:30 pm
content: Quote from: Rog520 on March 28, 2015, 05:16:35 pmSafe to work?, depends on how many millions of volts you're working with..

author: Bassman59
author_rank: Super Contributor
timestamp: March 31, 2015, 07:05:20 pm
content: Quote from: slim on March 28, 2015, 05:50:58 pmThat's not good enough -- those rods need to be connected to the neutral back at the service entrance.QuoteThe outlet ground may be floating many volts away from the neutral, so it's not safe. See above.

author: nanofrog
author_rank: Super Contributor
timestamp: March 31, 2015, 08:33:40 pm
content: Quote from: slim on March 28, 2015, 05:50:58 pmThe plugs used back then would have been 2 wire, but the metal box in the wall should be grounded (and bonded to neutral back in the breaker panel), assuming it was constructed to code (NEC). Cut the power, open the outlet, and look to see if the ground wire is screwed to the back of the box as it's supposed to (per NEC as of Oct. 1959). Easy enough to install a 3 prong outlet properly in this case.If that's not there, and you're correct on the construction date, then I'd suspect a DIY special or unlicensed contractor (i.e. no permits pulled and/or enforcement via inspection).Quote from: slim on March 28, 2015, 05:50:58 pmAssuming this is the only ground wire in those boxes, definitely check to see if neutral is bonded in your panel, and fix if necessary. Then I'd recommend installing GFCI's.