Getting Rid of Charges Part 4: Grounding the Charge

by Andy on February 20, 2012

While it is important to know how to keep yourself and your workstation grounded, it can be interesting to understand where your charge goes. Most ESD-safe products seem to whisk your charges away to a nebulous “ground”, but it is not always clear what that means. Typically grounding hardware connects to the earth, using its large neutral charge to negate any built up static on objects.

While talking about ionizers last week, we noted that opposite charges attract. This is what allows the ions to neutralize charges as they fall across a workbench. There is also a corollary rule: similar charges repel. If you have a build up on charges on objects (say too many electrons producing a negative charge) they naturally want to move away from each other. The problem is that they often have no place to go, until they come in contact with another device.

Wrist Ground By grounding yourself to the earth, you give the electrons a path to leave safely. Because the earth is so large, you will discharge fully whenever you are properly grounded to it. If you try to discharge to a small object then you may get rid of some of your charge, but probably not all of it, leaving both you and the object with enough of a charge to damage ESD sensitive devices. The earth, however, can easily support any charge that a device or human in a work area can normally generate, so it serves as a practically infinite container for any extra charge you may gain.

What makes the earth such a good ground? At first it may seem odd that the earth is used to neutralize charges in this way, especially as dry soil can be a very good insulator. The main reason it works so well is the moisture in the ground. Just as lightning can hit trees and travel to the ground through the rain on them (as wood is another great insulator), the moisture in the ground can serve as a great conductor for errant static electricity.

It is important to measure the soil resistivity wherever you are placing your ground, as you want it to be as low as possible. The lower the soil resistivity, the better your grounding system will work. Most times when you are grounding in a building you can use metal beams that are part of the framework, as long as they are driven into the earth and are suitably set up for this use. This can be a great method as these beams tend to be driven very deep in the earth, and the deeper they are set, the lower their resistance. If you do not have access to this framework, you can also connect to a metal rod set into the ground. With this method you need to test various areas to make sure you place the rod in the place with the least resistance, ensuring that the charge can easily make its way into the ground.

That ends our series on grounding. Make sure to check in next Monday for a new series of articles!

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