Surges and spikes are an increase in "normal" electrical line voltage that can cause serious damage to equipment. A surge measures less than 500 Volts and lasts less than 2 seconds.

Spikes are much shorter in duration, typically less than onethousandth of a second, but they can measure into the thousands of Volts.

• Lightning - a direct hit is usually catastrophic.
• Proximity Strikes - lightning strikes several miles away causing large voltage spikes along transmission lines.
• Brownouts / Blackouts - under-voltage or sag that is immediately followed by an unusually high voltage transient.
• Utility Grid Switching - utility companies switching transmission lines from one supply system to another.
• Inductive Loads - the switching on and off of electric motors inside or outside a facility (such as air conditioners or heavy machinery).