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E.S.D earth point
- Thread starter bluc
- Start date
Just setup a esd earth point which runs straight out to a earth stake. Is there someway I cant test it to make sure it works properly?
One way is to grab a DMM or similar and compare the potential between your earth point and an outlet, assuming it works the same as here in Europe (one DMM lead in outlet, other on earth point, should be 240VAC here, ~120VAC in other places). If it's significantly lower, there's some resistance along your path to ground and thus unsuitable as-is.
If it's significantly higher, you may have other issues
One way is to grab a DMM or similar and compare the potential between your earth point and an outlet, assuming it works the same as here in Europe (one DMM lead in outlet, other on earth point, should be 240VAC here, ~120VAC in other places). If it's significantly lower, there's some resistance along your path to ground and thus unsuitable as-is.
If it's significantly higher, you may have other issues
This method will not work to measure the resistance to ground. A DMM ideally can be modeled as an infinite resistance (same as open circuit). It is measuring the potential difference between your two points.
He is suggesting you measure the voltage to your ground wire from an outlet. The problem here is that no current should be flowing through your ground wire and by ohm's law: voltage = current * resistance. Therefore, if your current is 0 you can still have resistance and still have zero voltage at the other end.
However, there is another point here. While you should have good conduction to ground, normally ESD mats actually have quite a bit of resistance. If you were to shock yourself you wouldn't want to be connected directly to ground. And given what I just explained earlier if there is no current flowing through the mat as long as it is connected to ground even with a high resistance it will still have no potential for ESD. Static is usually high voltage but only a few electrons. This is why it can be grounded to an ESD mat through a high resistance and still be effective at dissipating the charge because it is not capable of supplying current to build that potential difference.
I know the words here may not have been perfect but I believe it should give you the right idea. You may want to ensure your ESD wrist band actually has a safety feature that gives it a high resistance to your ground strap (I think it is even a megaohm.. but I'm not sure). Also I believe a high resistance on your wrist strap or mat will slowly dissipate the charge rather then a quick spark which could damage electronics more easily. At work we sometimes can demonstrate this... we can build up static and see a spark if we carefully touch the edge of the mat near the bottom side with a fingernail rather than the top of the mat. I believe this is because the bottom of the mat is actually much more conductive while the top of the mat is resistive.
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You are precisely correct. The point of the anti-static wrist strap is two fold: to keep you grounded (and thus prevent static build-up in the first place), and to ensure that any built-up charge is dissipated nice and gradually.