Using ground of power supply for anti static strap? - Page 1
Forum section: electronics / beginners

author: Rodast
author_rank: Contributor
timestamp: September 03, 2013, 01:01:35 pm
content: Hello all,I was just wondering if I still have to fiddle around with adapters or the ground of my wall outlets or if I could just use the ground connector of my lab power supply instead to connect my anti static matt to it.My understanding is that ground is connected through to the wall outlet and the power supply does not even to be powered up using it this way.Is this correct?GreetingsRodast

author: KJDS
author_rank: Super Contributor
timestamp: September 03, 2013, 01:37:56 pm
content: It's fine, so long as your power supply is plugged in, hasn't developed a fault that you can't see inside the case and that in the event of a fault happening that you can't see you don't care about your circuit developing annoying faults with no obvious reason that could well take hours and $$$$ to sort out.Alternatively you could spend a few minutes and a few cents sorting it out properly now.

author: madires
author_rank: Super Contributor
timestamp: September 03, 2013, 01:55:21 pm
content: Yep, but check that with a DMM to be sure. And please add a 1MOhm resistor to limit the current (between the PSU's ground/PE and the anti static matt). If you buy a dedicated cable for connecting both it might already got that resistor.

author: Rodast
author_rank: Contributor
timestamp: September 03, 2013, 02:09:45 pm
content: Quote from: madires on September 03, 2013, 01:55:21 pmI can clearly see that the 1MOhm resistor is already included into the matt connector for the wrist band which also holds the cable to connect to ground.So it seems that I am ready to go.Thank you very muchRodast

author: george graves
author_rank: Super Contributor
timestamp: September 03, 2013, 03:04:31 pm
content: Quote from: madires on September 03, 2013, 01:55:21 pmQuestion: What's the reasoning behind that?Won't a static discharge take the path of least resistance? So if you develop a charge while wearing a strap, won't it rather go through your circuit them them 1M resistor? THE PSU ground should be earth referenced.(I, like many others, never bother with ground straps. And have never had issues, ever. But I do ground myself before picking up something like a PC mother board, or intel chip - 1 second of my time is worth a few $100 bucks.)

author: Unknown
author_rank: Unknown
timestamp: September 03, 2013, 03:09:59 pm
content: If the mat, your hand and your board are at the same potential because they're all connected (through 1 Mohm resistors), then no current will flow and no discharge will take place. Connecting a wrist strap (especially) hard to ground will create a very nice conduction path if your other hand happens to touch a mains conductor. The path of least resistance between your arms might be through your chest and heart. I wouldn't be as worreid about the mat, since the mat itself has a fairly high resistance anyway.

author: KJDS
author_rank: Super Contributor
timestamp: September 03, 2013, 03:21:04 pm
content: The resistor is there as it is possible that what you touch is charged. Without the resistor, the current flowing directly to ground can damage the part.

author: Unknown
author_rank: Unknown
timestamp: September 03, 2013, 03:50:51 pm
content: Wouldn't the human skin resistance be sufficient for that? I can't imagine an ESD puncturing the skin. Of course it would be a problem with something like a metal surface, but I don't think it would be much of an issue with a wrist strap or anti-static mat.

author: Rodast
author_rank: Contributor
timestamp: September 03, 2013, 04:19:51 pm
content: Well the whole thing come as a set.It consists of the matt with a plug (the plug includes the 1MOhm resitor).One end of the plug has the cable used for earthing which is normally supposed to be connected to the earthed terminal of a wall outlet.To the other end of the plug you connect the wrist strap.Since I simply don't want to mess around with the wall outlet my idea was to not use that ground but the one provided by my lab power supply (which seemed to be much safer at first thought).Hope we can all agree on that.I guess the matt is only connected so that the cable is fixed to something on the table so you don't wear a 3+ meter long cable at your wrist which could be quite distracting.To give some more details this is the part I bought and want to use:http://www.lindy.co.uk/components-tools-c7/tools-tool-kits-c339/anti-static-service-kit-p4356

author: G7PSK
author_rank: Super Contributor
timestamp: September 03, 2013, 04:20:26 pm
content: A few kilo volts would easily penetrate the skin, I understood the 1M resistor was for current limiting, but this line brings up another point, most scopes have a ground socket on the front panel, has any one ever used this for any purpose, or is it just a hang over from the days of all banana sockets on scopes pre BNC days I have wondered about using it for my esd strap but to date have always used the special plug.

author: AG6QR
author_rank: Frequent Contributor
timestamp: September 03, 2013, 05:17:22 pm
content: There are two reasons for the megaohm resistor.One is ESD, to allow charges to equalize slowly instead of in a quick sparking zap. The other is human safety in case you touch energized mains or another energetic power source, either through a careless oversight on your part of through a malfunctioning power supply or something like that.As far as whether to ground through a scope, a power supply, another instrument, directly to the mains ground, or directly to a cold water pipe, any of the above will work, as long as the integrity of the path is good. Some of those choices make it a bit harder to verify the integrity of the ground path.Actually, as far as ESD is concerned, it doesn't matter much whether you're at ground potential or at some other potential, even kilovolts away from ground. What's important is that you and all the pins of every device you touch are always equalized at the same potential. Getting everything to ground is the simplest way to do this.