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The type of electrical power supplied by the power utility. This electrical current reverses direction at regular intervals.

A measurement of the flow of electrical current.

The magnitude of alternating voltage/current measured from 0 during one oscillation wave cycle.

Total loss of electrical power.

Any variation in AC voltage that is below normal established limits for longer than 2.5 seconds. Causes erratic operation of equipment, power shutdown, output errors, and motors run "hot".

The voltage at which MOV (metal oxide varistor) will begin clamping at minimal current.

The movement or flow of electricity. The flow of current is measured in amperes.

The type of electrical power stored in batteries and generated by solar electric devices. The electrical current flows in a single direction.

Electrical disturbances, a form of distorted electrical power, come in many shapes and sizes. Electricity as it comes from the generator is smoothly flowing and shaped like successive waves cycling up and down 60 times per second.

Over voltage

Over voltage conditions are steady-state RMS voltage variations above limits (say plus 10 percent of nominal equipment voltage) for longer than 2.5 seconds. Over voltage conditions cause electronic component heating with the potential for immediate or future component failure through overstressing. If this heating effect causes enclosure temperature to rise above the safe limit the system may shut down.

Under voltage

Steady-state RMS voltage variations below established limits (say minus 10 percent of nominal equipment voltage) for longer than 2.5 seconds. Under voltage conditions can cause erratic equipment operation and possibly system shutdown, as well as output errors.

Harmonics

Periodic wave distortion and multiple frequencies causing over heating, component damage, erratic operation, poor control, and telecommunication disruption.

EMI (Electromagnetic Interference)

Unwanted disturbance or noise caused by another electrical circuit or equipment. The disturbance may interrupt, obstruct, or otherwise limit the effective performance of the circuit.

Momentary Outage

Also called a "momentary" this type of power outage is generally caused by utility protective equipment operation when trees, animals, vehicles, lightning or other contact utility wires or striking the utility pole.

RFI (Radio Frequency Interference)

Undesirable noise produced by a power supply or other electrical or electronic device during its operation. RFI, in power supply technology, is usually taken to mean the same thing as Electro-Magnetic Inference.

Transient

An erratic power disturbance to include surges, spikes, glitches, and even sags. However, the most troublesome and destructive are the irregular over voltage fluctuations…sudden, extreme increases in voltage.

Sags/Dip

Short-term RMS voltage variations below established limits for less than 2.5 seconds. Sags can cause computer memory loss, bit errors in data transmission, power supply damage, and erratic telephone switching system performance. Equipment shutdown can easily occur if a system confuses large sag with a power failure.

Swell

A brief increase in the normal voltage level. Most swells are caused when a motor stops. Although not generally a problem, swells have been known to cause failure of marginal components in electronic equipment.

See Electrical Disturbances

An electronic device that blocks out specific frequencies, which could compromise power output.

Normally occurs with transformer-based UPS units that overload in current.

A loss or break in frequency for duration less than one cycle where the frequency is reestablished out of its original pattern. Standby "Switching" UPS systems can be the cause of this event.

A variation of AC line frequency above or below 60Hz.

When used in reference to utility power, it refers to a system of electrical transmission and distribution lines.

See Electrical Disturbances

Unit of measurement of frequency (number of cycles per second). Measures the rate at which AC electricity reverses itself.

Short-term, high-magnitude transients, which severely distort the shape of the waveform. Voltages can rise to hundreds or even thousands of volts for time periods varying from a fractions of a microsecond to a few milliseconds. Transients are the most insidious type of disturbance since they can occur without any indication to system operators. Their effects are far reaching through such problems as semiconductor degradation, bit errors in memory and data transmission, and erratic system performance.

A device that converts DC power to AC power.

The electrical separation of the input and output via the transformer.

The maximum amount of energy the device can absorb. This term has implications as the life and let-through voltage in absorptive types of surge suppressors. A 6000 volt 3000 ampere 8 x 20 microsecond surge (IEEE 587 B spec) can deliver about 33 joules to an absorptive suppressor (Metal Oxide Varistor - assuming MOV voltage of 550 volts at 3000 amperes). This means that a commonly used 38 joule (144mm) MOV might fail after a few major surges.

One thousand watts of electricity. Ten 100-watt light bulbs use on kilowatt of electrical power.

See Electrical Disturbances

Signals that are embedded or overlaid onto incoming power. These signals take the appearance of fuzz or scribble on a power waveform. Fuzz or scribble can be interpreted as data when it passes through a processor of electronic equipment causing contamination of instructions. In most cases noise will not cause physical damage to equipment. However, noise can cause equipment to malfunction and result in a loss of data. A few categories of noise are:

• High Frequency Noise
• Low Frequency Noise
• Harmonics
• EMI/RFI Interference

See Electrical Disturbances

A control circuit which shuts down the power supply in the event of an over voltage condition.

The ratio between the true power (Watts) and apparent power (Volt Amps) a power factor of 1.00 is unity.

Used to describe how quickly tile surge protective circuitry will begin to clamp or suppress the surge. Be aware that all ratings are "component ratings" even though the manufacturer does not state such.

See Electrical Disturbances

A measurement of effective power

See Electrical Disturbances

A "sinusoidal" or "sine wave form" represents AC power graphically -called sine wave for short. It is the optimal output wave form of alternating current (AC). A sine wave, normally changes (cycles) 60 times every second in North America and 50 times every second internationally.

Pictured at the right is a perfect or pure sine wave, which is required for correct functioning of today's sensitive electronic equipment.

Power coming from the utility is seldom a pure sine wave. Surges, spikes, brownouts, sags/dips, noise (signals that are embedded or overlaid onto incoming power), harmonics (periodic wave distortions and multiple frequencies), frequency variations and shifts - and other power abnormalities adversely affect incoming power. Systems protecting power must be able to handle all of these abnormalities and provide a pure sine wave to equipment.

An impulse, high-magnitude, short-duration power disturbance. Spikes can damage equipment, reduce service life, and lose or alter data.

A square wave is an instantaneous voltage rise and fall, generated by minimal switching of positive and negative voltage sources. Such waveforms cause induced harmonics and damaging current inrush to equipment. Square wave outputs are inexpensive to produce. Some UPS manufacturer will market and label a "Square wave" as a "Modified Sine wave".

Beware of systems which produce square wave outputs. They are inexpensive to produce and purchase, but are damaging. Some UPS manufacturers will try to deceptively promote them as a sine wave equivalent.

Protection which covers a broad time and joule spectrum. In most cases multistage protection is obtained by using different types of devices with varying characteristics of speed and joule rating.

Short-term RMS voltages of low-magnitude that exceed limits for less than 2.5 seconds. Surges can cause computer memory loss, bit errors in data transmission, power supply damage, and erratic telephone switching system performance.

See Electrical Disturbances

See Electrical Disturbances

The difference in electrical potential between two points of an electrical or electronic circuit, expressed in volts (V).

A measure of the "apparent" power equivalent to the true power (watts) in resistive loads, but exceeding watts in non-resistive loads. VA is calculate by multiplying volts times amps without using power factor.

A quantitative measurement of electrical power (1 Joule = 1 watt-second)