It is unfortunate, but a fact of life. Computers, computer-related products and process control equipment used in data communications can be damaged by high-voltage surges and spikes, and are susceptible to noise induced by ground-loop currents.

Such power surges and spikes are most often caused by lightning strikes. However, there are occasions when the surges and spikes result from any one of a variety of other causes. These may include;

  • Static from human equipment users.
  • Potential differences between grounds to which different equipments are connected.
  • Noise on interface cables.
  • Direct contact with power/lightning circuits.
  • Static build up on cables and components.
  • High-energy transients coupled into equipment from cables in close proximity.
  • Miswired systems.

Human equipment users who have accumulated large static electricity charge build-up on their clothing can cause problems for computer equipment. In fact, electrostatic discharges from a person can produce peak voltages up to 15 kV with currents of tens of Ampers in less than 10 microseconds.

Data-interface lines that have different potentials relative to earth-ground connections can also cause problems. They can generate severe ground current noise when connecting a computer with terminals in remote buildings or different areas of one building. A few volts of potential difference can interrupt communications and damage equipment.

Noise on the interface cable can also disrupt sensitive analogue circuits. Acting as an antenna, the cable couples high-frequency noise through the interface device, then through the power supply and into the analogue circuits. Isolation eliminates this problem and other data-interface problems.

Optically isolated communication adapters provide an electrical barrier between physically connected devices. The serial data is passed though optical couplers which electrically separate the equipment. Adapters with isolation voltage ratings of 500V to 3000V are available. Surge protection is designed to eliminate short high voltage transients that can be generated in industrial environments.

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