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Electrostatic Discharge Precautions

📄 Contents

  1. Identifying and Avoiding Electrostatic Discharge
  2. MOS-Handling Techniques
  3. Understanding Grounds
  4. About This Article
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If you're a hardware service technician preparing for the Core Hardware module of the A+ Certification examination, let Charles J. Brooks, author of A+ Certification Training Guide, Third Edition, help you by explaining how to upgrade and optimize system performance. He offers clear guidelines and helpful test tips so you can pinpoint areas that need more study and concepts you need to master to pass the exam.
This article is adapted from A+ Certification Training Guide, Third Edition, by Charles J. Brooks (2001 Charles J. Brooks and Marcraft International Corporation, ISBN 0-7357-1088-0), part of New Riders Publishing's Training Guide Series.

Electrostatic Discharge Precautions

This article addresses the following objective in the "Domain 3.0: Preventive Maintenance" section of the A+ Certification exam:

  • 3.2: Identify ESD (electrostatic discharge) precautions and procedures, including the use of ESD protection devices.

The first way to avoid electrostatic discharge (ESD) is to be able to identify when and why it occurs.

Identifying and Avoiding Electrostatic Discharge

What Is ESD?

Electrostatic discharges are the most severe form of electromagnet interference (EMI). The human body can build up static charges that range up to 25,000 volts. These buildups can discharge rapidly into an electrically grounded body or device. Placing a 25,000V surge through any electronic device is potentially damaging to it.

Static can easily discharge through digital computer equipment. The electronic devices used to construct digital equipment are particularly susceptible to damage from ESD. As a matter of fact, ESD is the most damaging form of electrical interference associated with digital equipment.

Test Tip

Remember what the acronym ESD stands for.

The following are the most common causes of ESD:

  • Moving people

  • Low humidity (hot and dry conditions)

  • Improper grounding

  • Unshielded cables

  • Poor connections

  • Moving machines

Test Tip

Memorize the conditions and actions that make ESD more likely to occur.

When people move, the clothes they are wearing rub together and can produce large amounts of electrostatic charge on their bodies. Walking across carpeting can create charges in excess of 1,000 volts. Motors in electrical devices, such as vacuum cleaners and refrigerators, generate high levels of ESD.

Test Tip

Compressed air can be used to blow dust out of components and it does not create ESD.

ESD is most likely to occur during periods of low humidity. If the relative humidity is below 50%, static charges can accumulate easily. ESD generally does not occur when the humidity is above 50%. Any time the charge reaches around 10,000 volts, it is likely to discharge to grounded metal parts.

Although ESD will not hurt humans, it will destroy certain electronic devices. The high-voltage pulse can burn out the inputs of many integrated circuit (IC) devices. This damage might not appear instantly, but it can build up over time and cause the device to fail. Electronic logic devices, constructed from metal-oxide semiconductor (MOS) materials, are particularly susceptible to ESD. The following section describes special handling techniques to observe when working with equipment containing MOS devices.

High Voltage, Low Risk to Humans

You might be a little confused by the warning about the lethal 25,000 volts inside the monitor and the statement that 10,000 to 25,000 volts of ESD are not harmful to humans. The reason for this is the difference in current-delivering capabilities created by the voltage. For example, the circuitry in the monitor and the power supply is capable of delivering amps of current, whereas ESD's current-producing capabilities are less than a thousandth of that. Therefore, the 120V AC, 1-amp current produced by the power-supply unit is lethal, but the 25,000V DC, microamp current produced by ESD is not.

Test Tip

Remember that the current capabilities of electrical devices establish the potential danger levels associated with working around them.

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