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Topic: grounding for anti esd (Read 356 times) previous topic - next topic

secretreeve

bit random and my head it works, just want to confirm it,

if you take a 3pin plug with metal earth pin, attatch a wire from the earth pin to your mat and wrist strap, that will be fine for grounding esd and saving your circuitry from it right?

obviously i dont generally recommend tethering yourself to the household mains as if theres a short somewhere else you'll get zapped but i need a short term solution as keep killing mosfets from static as i move around as my workstation is a standing one not a seating one (too high for a chair and need to buy a stool)

groundFungus

#1
Nov 14, 2019, 03:45 pm Last Edit: Nov 14, 2019, 03:46 pm by groundFungus
An anti static wrist stat does not connect straight to ground.  The ones that Ihave  used* have 1 Meg Ohm resistance in line.  That is so the charge "bleeds" off so sparks are not generated.

*Working with electrically initiated explosive devices.

PerryBebbington

bit random and my head it works, just want to confirm it,

if you take a 3pin plug with metal earth pin, attatch a wire from the earth pin to your mat and wrist strap, that will be fine for grounding esd and saving your circuitry from it right?

obviously i dont generally recommend tethering yourself to the household mains as if theres a short somewhere else you'll get zapped but i need a short term solution as keep killing mosfets from static as i move around as my workstation is a standing one not a seating one (too high for a chair and need to buy a stool)
Yes, that's fine. The household earth is 'supposed' to be safe, that's what it's for. Your water and gas pipes should be connected to it, and you don't worry about touch a tap or radiator. However, if in any doubt at all get a qualified electrician to test your house wiring and recommend and upgrades needed.

srnet

The resistor prevents excessive current running through your body (and across your chest) from the working hand to the 'grounded' hand.

If you grab a 'safely earthed' copper pipe with one hand, then imagine what might happen if you touch something live with the other hand.

http://www.50dollarsat.info/
http://www.loratracker.uk/

srnet

#4
Nov 14, 2019, 09:41 pm Last Edit: Nov 14, 2019, 09:42 pm by srnet
bit random and my head it works, just want to confirm it,

if you take a 3pin plug with metal earth pin, attatch a wire from the earth pin to your mat and wrist strap, that will be fine for grounding esd and saving your circuitry from it right?

obviously i dont generally recommend tethering yourself to the household mains as if theres a short somewhere else you'll get zapped but i need a short term solution as keep killing mosfets from static as i move around as my workstation is a standing one not a seating one (too high for a chair and need to buy a stool)
The short term solution is to use a proper anti static wrist strap, the type includes a high value resistor, so that you dont increase the risk of killing yourself.  
http://www.50dollarsat.info/
http://www.loratracker.uk/

gilshultz

You are working with the most important tool on your bench. It will save you a lot of time and trouble over the years tracing problems that are ESD damage. Test it regularly, I do it every day. According to the NEC if it is properly wired the ground pin is connected directly to earth ground, It is not to be used to conduct current except during a fault which should trip the breaker and must be sized to accomplish this.  Typically the single ground is connected to the neutral at the entrance at one point only and no where else.  This is typically accomplished with a bonding screw. This can be tested with a tester costing a few bucks. Currently it is no longer required to bond to the gas pipes however this depends on which version of code your area is using. Our water pipes are plastic. The code changes every three years and is re issued. If it is properly installed a short in another part of the system will not effect you by more then a few hundred millivolts depending on the magnitude and type of fault that is why it is there. If you are in the US your entrance in our area needs 4 wires in total: 2 phases, 1 neutral and 1 ground which should be a continuous wire from the main panel to the water pipes etc, it it not to be spliced but can be welded. As far as resistors in the ground strap and ground mat it is part of the unit when you purchase it.  Mine are  metal expansion (watch band style) with a coiled cable.  The resistor is the coiled cable there is no other resistor.  Purchase a NEC code book it can keep you reading for a long time.
Good Luck & Have Fun!
Gil





Paul__B

If you grab a 'safely earthed' copper pipe with one hand, then imagine what might happen if you touch something live with the other hand.
And that's the point.  If you are working with mains or anything like it, you really do not want to be grounded, and who knows what is sitting on your workbench!  :smiley-eek:

If - and only if - everything is correctly wired, then your outlet ground pin will be ground so that your toaster, washing machine etc. will indeed be grounded as they must be.

To be really sure, your 1M resistor could be five 180k resistors in series, in a piece of plastic tubing.

krupski

bit random and my head it works, just want to confirm it,

if you take a 3pin plug with metal earth pin, attatch a wire from the earth pin to your mat and wrist strap, that will be fine for grounding esd and saving your circuitry from it right?
Everyone overthinks ESD protection. What can zap a device is a potential difference between your body and the part you are working on. Being "grounded" is irrelevant.

In reality, you don't need those fancy wrist straps, air ionizers or conductive mats. All you need is to make your body potential equal to what you are working on.

Example... inserting a card into a PC... just hold the card in one hand and touch the PC frame with the other hand. Any potential difference between you and the PC is eliminated. Now, install the card. No ESD gadgets required.

Example... filling your car gas tank... hold the gas nozzle in one hand, touch the car with the other hand. Any charge is eliminated and its now safe to insert the nozzle into the filler hole.

I never use wrist straps or grounding gadgets and I've never zapped a part with ESD.
Gentlemen may prefer Blondes, but Real Men prefer Redheads!

Grumpy_Mike

While I agree with kurpski  Have you seen this product, there are lots like it.

https://www.antistat.co.uk/product/earth-plug-1-x-10mm-stud-with-1meg-resistor/

gilshultz

I work on mains voltages a lot, the simplest solution is to isolate the mains, then I do not have to isolate all the test equipment.  There is a course at: https://www.automatedlearning.com/products/esd_index.html that might help.  "If you grab a 'safely earthed' copper pipe with one hand, then imagine what might happen if you touch something live with the other hand. " Actually any ground will do, even the neutral line! Food for thought: Why do all the semiconductor manufactures spend a lot of money fo have everything grounded, pans, tubs, people, tools, etc.
Good Luck & Have Fun!
Gil

MorganS

There is probably a piece of equipment on your workbench that has a 3-pin plug. A power supply, solder station or oscilloscope. If it has a metal case then that metal is grounded.

If it has screws in the case, you can easily put a wire under a screwhead and ground your ESD mat and wrist strap there. Much less scary-looking than a wire to the mains plug although it is electrically identical.
"The problem is in the code you didn't post."

PerryBebbington


Quote
Why do all the semiconductor manufactures spend a lot of money fo have everything grounded, pans, tubs, people, tools, etc.
As far as I know, and maybe there is someone reading this who works for a manufacturer who can correct me or confirm, so that there is no risk of static electricity build up, which would be disastrous in semiconductor manufacture.

secretreeve

i love this thread, its so interesting to see all the different replies and how they vary with the information yet is generally consistent. its informative and enjoyable to read through. annoyingly all my desk equipment at the moment has plastic cases so no metal frame to be grounded.

makes alot fo sense what people have been saying. but for smaller circuits its not so good to touch the circuit and the component i dont think. not to balance esd anyways

Paul_KD7HB

Yes, all the replies are very interesting and mostly right-on! However, no one has mentioned that ESD damage is CUMMULATIVE. That means the first or third or 4th jolt will not stop the device, but the 5th will kill it.

As a manufacturer of electronic circuit boards, my company is/was probably the first in line to cause ESD damage. So we are/were very careful not to be the first to cause an EDS discharge. In 20 years we have not had a product returned due to ESD damage.

And the company is now closed and all the equipment is up for auction sale.

Paul

Grumpy_Mike

When a chip fails in manufacturing it is a big deal especially at the start of a new product. Any unexpected new chip is particularly suspect, is it chip manufacture, is it a design error or is it a product assembly matter?

Often the chip is sent back and is decapuslated, or X-rayed to see what what the cause of the failure. This often proves to be ESD damage, which the chip manufacturers are keen to blame the product assembly, so to limit their liability, which can be great if this is a significant percentage, such as 5 to 10%.

This can trigger "Epidemic failure " clauses in contracts and can cost a great deal of money. ESD precautions in the factory are an attempt to mitigate this, and control everything that can be controlled.

While many engineers will never have seen an ESD failure they are only handling a very small number of components compare to an assembly line.

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