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Zapping Things With ESD Ė Just One More Service I Offer

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MeasurementBlues
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What ground is actually good for.
MeasurementBlues   8/13/2014 5:01:27 PM
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MeasurementBlues
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Ground? What ground?
MeasurementBlues   8/13/2014 4:58:10 PM
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Having just returned from the EMC Symposium, I'm reminded that there is, as Bruce Archambeault will tell you, there's no such thing as ground except perhaps in this case, for safety.

Too often, we use the term "ground" when we really mean "return" as in current returning to its source. Ground is a reference voltage. Current shuld not flow through a ground wire at all. When it does, you have samety and EMC problems.

Read what Dr. Todd Hubing said last week about "ground" at an EMC fundamentals tutorial.

 

Wnderer
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power strip and ground plug adapter
Wnderer   8/13/2014 4:07:48 PM
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Get a powerstrip and one of these $7 ground plug adapters. With a power strip you'll have a circuit breaker and switch to help shut down things quickly if there's trouble.



ninja'd by elizabeth

elizabethsimon
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Re: Maybe...
elizabethsimon   8/13/2014 4:04:07 PM
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I did something similar when I had to set up on a table that was inconvineiently far from a wall socket. Since I needed a multi lead outlet strip with a long cord to power the equipment, I attached the cable from the antistatic mat to a ground on the outlet strip (which was located on the far side of the table). I then attached the lead from the wrist strap to a banana jack at the grounding point on the antistatic mat (which was on the edge near the front of the table). This minimized the stretching of the wrist strap cord and the whole thing could be moved fairly easily by unplugging the outlet strip from the wall and rolling it (and the cables) inside the antistatic mat.

 

Max The Magnificent
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Re: Maybe...
Max The Magnificent   8/13/2014 3:55:44 PM
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@mhrackin: ...and i noticed that they have a TWO-WIRE UNGROUNDED (and unpolarized) AC plug.

1,000 curses-- you are of course 100% correct -- in fact Ivan came bouncing into my office about 30 minutes ago saying the same thing -- and as soon as he said it I remembered that my notepad also has a 2-pin power plug.


Bummer ... watch this space...

mhrackin
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Re: Maybe...
mhrackin   8/13/2014 3:55:43 PM
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Max, the use of the USB and the use of the power strip are NOT mutually exclusive!  It would make sense to use the power strip regardless, just to reduce the excess bending over (although perhaps the exercise is beneficial!). I'd still vote for plugging directly into the U-ground hole rather than depending on the combined continuity of the series chain of alligator clip to USB shield wire to PC USB connector through PC internals to DC ground of power jack to power supply, thence (maybe) to the U-ground of the power cord into the AC outlet!  Far too many points of failure there (and of the most unreliable system element: interconnections!).

mhrackin
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Re: Maybe...
mhrackin   8/13/2014 3:45:57 PM
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I don't know what flavor notepad you are using, but I have a number of Lenovo Thinkpad power supplies on my desk right now, and i noticed that they have a TWO-WIRE UNGROUNDED (and unpolarized) AC plug.  I also have some ancient Dell ones with 3-wire cords.  Obviously, there's no point in ohming out the Thinkpad ones as there is NO input ground.  The Dells do have the ground continuous (1.2 ohms) to the shell of the DC power plug.  However, these are REALLY old (from XP PCs) so your results may differ.

Max The Magnificent
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Re: consumer versus industrial
Max The Magnificent   8/13/2014 2:41:38 PM
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@dt_hayden: If you grab the "ground" to make your connection, you could potentially make a direct discharge at that point.

Good point

Max The Magnificent
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Re: Notebook??
Max The Magnificent   8/13/2014 2:39:47 PM
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@Antedeluvian: I hope I am not alone in noticing that a notebook can run on batteries, in which case you have no ground at all.

True, but I never use it that way -- I always have it plugged in when I'm working on a hobby project.

dt_hayden
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consumer versus industrial
dt_hayden   8/13/2014 2:37:02 PM
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In general, grounding yourself through a piece of (consumer grade) electronic equipment for ESD control seems like a not so good idea.  You are making assumptions about the goodness of that ground and assuming the equipment can withstand discharges into that point.  If you are sure only the wriststrap connection touches the "ground" point, then currents are limited by the resistor in the strap anyway and less of a worry.  If you grab the "ground" to make your connection, you could potentially make a direct discharge at that point. 

Having said that, Tek scopes I have used in the past had a "grounded" banana jack on the front panel which I plugged into for ESD management.  My thinking was since it was industrial gear, Tek designs robust equipment, and the point was probably put there for that purpose, it was fine. 

If you are only dealing with isolated portable gear, I think it is more important to equalize potential to the gear, rather than to ground.  .I have clipped onto grounds of gear in these cases.  In this case, some (all?) soldering ground tips are grounded, so beware when soldering.

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