ESD Facts

Static electricity is the accumulation of an electric charge (produced by friction) on a non-grounded object. The static charge on the surface of a non-grounded object can jump when it contacts the surface of any grounded object. This electric discharge is known as electrostatic discharge (ESD). ESD can be very destructive to a computer.

The threat of ESD begins when the fragile components (including the processor, hard drives, memory, motherboard, and expansion cards) inside the computer are exposed. Damage can occur simply by placing a fingertip too close to a component inside an open computer case. ESD charges can travel through wires and into components, where the wires can explode or fuse together, causing the components to fail. There are two types of failure caused by ESD:

  • Catastrophic failures cause components to fail. The only solution for a failed component is to replace it.
  • Upset failures degrade components, leading to ongoing or intermittent problems or eventual failure. With these types of failures, it is difficult to identify the source of the intermittent problem or even know if damage has occurred.

The table below illustrates just how serious a threat ESD can be to an electrical component.

Event / Charge Created (Volts)
Average computer component's operational power / 3 to 5
Destroy a computer component's circuit / 100 (or less, especially with low relative humidity)
Physically feel a shock / 3,000
Visually detect a spark / 8,000

The effects of ESD can be magnified by air temperature and humidity. Cool air is generally less humid than warm air. Therefore, ESD is more likely in the cool, dry air that is common during the winter months. Use the chart below to examine how low and high humidity levels affect ESD generation.

Activity / Charge Created (Volts)
High Relative Humidity (Humid Air) / Low Relative Humidity (Dry Air)
Walking over a vinyl floor / 250 / 12,000
Moving a plastic bag / 1,200 / 20,000
Walking across a carpet / 1,500 / 35,000

Precautions against ESD include:

  • Use antistatic mats under the PC and on the floor.
  • Discharge yourself before touching any computer component.
  • When touching anything inside the computer, wear an antistatic wrist strap that is attached with an alligator clip to the metal PC chassis.
  • Ground both yourself and the computer to the same ground. This provides a single path for the flow of electrical potential.
  • Use static resistant materials to handle computer components.
  • Never touch the metal connectors on a circuit board.
  • Avoid dry air in the computer repair location.
  • Keep computer repair location free of materials that accumulate electric charges (for example, plastic or Styrofoam).
  • Store sensitive components in static-shielded bags (also called anti-static bags; they are usually tinted gray). Static resistant bags are not near as effective (usually tinted pink or blue).
  • If a wrist strap is unavailable, keep your body in constant contact with the metal frame when working inside the computer.
  • Keep the relative humidity high (over 70%).

Note: Unplug the system before working on internal components. Do not rely on the power cord for an electrical ground.