Power problems can occur in two forms:


problems or disturbances that occur with a mains supply. Here we are concerned with Power Quality issues.
when the mains supply completely fails. Here we are concerned with how to keep systems running and business continuity.
Power supply problems are caused by various sources, for example distribution network faults, system switching, weather and environmental conditions, heavy plant and equipment or simply just faulty hardware. Regardless of the cause of the problem, the result will include one or more of the following types of power problems:

Sags: are short duration decreases in the mains supply voltage which generally last for several cycles. They are one of the more common forms of disturbances. When sags occur sensitive equipment can lock or hang causing data loss and system resets.

Surges: are short duration increases in the mains supply voltage which generally last several cycles. When surges occur equipment can suffer from premature failure. The high voltage causes wear and tear and general component degradation. This may not be noticeable until failure, though heat out is a good sign.

Transients and Spikes: these are very fast high energy surges lasting only a few milliseconds. When transients or spikes occur equipment can lock or hang, crash and even suffer damage which inevitably causes data loss and corruption. Large transients can occur from local or worst case a direct lightning strike.

Electrical Noise: this is a high frequency noise either common or normal mode which can cause severe disruption and damage to circuits and equipment.

Brownouts: are long term sags in the mains supply voltage which can last up to several days. During a brownout equipment can reset or even shutdown.

Blackouts and Mains Failures: when the mains supply fails completely this is known as a total mains failure or blackout. A break in the mains supply of only several milliseconds is sufficient enough to crash, lock or reset many of the components that make up a typical data or voice processing IP network, such as PC, terminal, console, server, PBX, printer, modem, hub or router.

A survey can be used to identify the types, duration and magnitude of power problems experienced on a site.

Switched Mode Power Supply (SMPS)

Most IT equipment is connected to the mains supply via a built-in Switched Mode Power Supply (SMPS). The SMPS is used to convert the incoming alternating current (AC) into the various levels of direct current (DC); the direct current is required to supply power to the various internal circuits and components such as: motherboards, drives, communications or USB devices.

Switch mode power supplies are designed to work from a clean, stabilised and regulated sinewave supply. This is a perfect mains scenario with no sags, surges, transients and spikes, electrical noise and brownouts. Whilst the occurrence of some of these in the mains supply at low magnitude and duration may not present the switch mode power supply with operational problems they can cause component degradation and reduce overall reliability. Off course any break in the supply can lead to a complete crash.