Transient Sources - Internal

Most transients are generated inside a facility. The three main internal causes are - device switching, electrostatic discharge, and arcing. Only lightning remains a wholly external, environmental transient source.

The switching of large inductive loads such as oil burners, air conditioners or other large motors can induce large transient voltages. Static electricity can generate up to 40,000 volts, with 25,000 volts being realistic in actual daily environments. Touching a computer keyboard, when this type of potential exists, may get your immediate attention as well as do serious damage to your computer. Humidity greatly affects the hazard of static electricity. Fifty percent Relative Humidity (50% RH) is really no problem, but is disastrous at 20% RH; the lower the humidity, the greater the static hazard.

Arcing can originate in poor or loose electrical connections, or it can result from dirty brushes on older motors. Voltage jumps across a gap not unlike a static discharge. When an arc occurs, high frequency voltage spikes result and spread throughout the facility wiring system. You'll probably see sparks and hear a zap or even smell the burnt insulation.