FAQs - Power Protection Glossary

A selection of power protection related frequently asked questions including industry term definitions.

Over voltage are: any higher voltage than that agreed as a regulated voltage in a circuit.

Radio Frequency Interference (RFI) are radio waves of sufficient intensity to be absorbed by a circuit and to cause a circuit malfunction.

RoHS stands for Restriction of Hazardous Substances, Directive 2002/95/EC.

WEEE stands for Waste Electrical and Electronic Equipment, Directive 2002/96/EC.

A Waveform is a graphical representation of the shape of a wave on a measure device like an oscilloscope.

Volt (V or kV or MV) is a measure of electrical force or pressure, which can be expressed as Vac or Vdc.

Triplens (Triple-N) are a multiple of the third harmonic in a waveform.

Total Harmonic Distortion (THDi) is a measure of all the harmonics induced in a system compared to a normal sinewave.

Transients are high energy burst voltage disturbances, with a short duration, superimposed onto the normal supply.

Under voltages are a voltage below the set regulated voltage for an extended period.

Transfer Time is the time it takes to transfer a load between ac supply sources such as a mains power supply, two mains power supplies or a combination of a mains power supply and UPS output. In a UPS system, transfer time can refer to the time it takes to  transfer the load to the inverter in an off-line or line interactive UPS. Also known as Switching Time.

A Transient Voltage Surge Suppressor (TVSS) is a device using MOVs, SAD/MOVs or GDTs to attenuate a transient or spike.

Brownouts are long duration decreases below nominal (the normal mains power supply voltage), which can last for many cycles or longer.

Direct Current (dc) is electric current the electrons of which are flowing in one direction only.

A Gas Discharge Tube (GDT) is an arrangement of electrodes in a gas within an insulating, temperature-resistant ceramic or glass case which switches to a low-impedance when subjected to a spike or transient voltage.

An Harmonic is a variation of a mains power supply sinewave above the fundamental (50 or 60Hz).

High Voltage (HV) is an alternating current (AC) supply in excess of 1000V. In the UK the majority of HV sites are supplied 11,000V (11kV).

An Harmonic Filter is a device to reduce the harmonic distortion generated by a device and enable it to provide a high power factor to its alternating current (AC) source.

Blackouts is a term used to describe a mains power supply failure, also referred to as an Outage.

A Clamping level is  the level at which a spike or transient protection device clamps the voltage down to a lower level.

Common Mode Noise is a form of high-frequency electrical noise which results from disturbances between the supply lines and earth (phase-to-earth or neutral-to-earth).

Dynamic Stability is the ability of a device to respond to a load-step change and deliver a stable output voltage waveform.

Electrical Noise is a high frequency noise on a sinewave and may be either Common Mode or Normal Mode.

Electro-Magnetic Compatibility (EMC) is the extent to which an electronic or electrical device will tolerate and generate Electro-Magnetic Interference (EMI).

Electro-Magnetic Induction is the production of an electrical potential difference (or voltage) across a conductor, situated in a changing magnetic flux.

Electro-Magnetic Interference (EMI) is a type of electrical noise that causes an electro-magnetic disturbance.

A Metal Oxide Varistor (MOV) is a device capable of absorbing very high surge currents without damage to itself.

Normal Mode Noise is a form of high-frequency electrical noise, that occurs between phase and neutral.

A Linear Load is a load in which the relationship between voltage and current is constant, based on a relatively constant load impedance.

Power Outages is an American term used to describe a mains power supply failure, also referred to as a Blackout.

Resilience is the capacity of a power protection system potentially exposed to hazards to adapt, by resisting or changing in order to reach and maintain an acceptable operational level.

An Ingress Protection (IP) Rating is a number used when specifying the environmental protection offered by enclosures around electronic equipment. The first number refers to the protection against solid objects and the second against liquids.

KVM stands for Keyboard Video and Mouse, and is an IT hardware device that allows control of more than one server or computer over a network using a single configuration of Keyboard, Video Monitor (screen) and Mouse.

Sags or Dips are short duration decreases, below the nominal mains power supply voltage, lasting several cycles.

Non-linear loads are loads in which the relationship between voltage and current fluctuates based on an alternating load impedance.

Noise Level is normally measured in decibels (dB) or (dBA). Noise may also be referred to as electrical noise in a circuit.

Crash Kits are spares kits held on-site to enable a fast emergency response to a system failure.

Recovery Time is the time incurred to obtain a fully regulated voltage after switching loads onto a standby generating set.

A Fixed Cellular Terminal (FCT) is a communications device that can receive and route telephone calls through a built-in mobile phone capability.

Surges are short duration increases in voltage above the mains power supply nominal, which generally last for several cycles.

Switching Time is the time it takes to transfer a load between ac supply sources. Also known as Transfer Time.

A Switched Mode Power Supply (SMPS) is a type of PSU with a non-linear current draw, most commonly found within computer, telecommunications and electronic devices.

Static Stability is the ability of a device to deliver a stable output voltage waveform under stable load conditions.

Low Voltage (LV) is an alternating current (AC) less than 1000V. An LV supply in the UK from a DNO is 400Vac three phase or 230Vac single phase +10/-6%.

Form Factor in a data centre is the size, configuration, or physical arrangement of a computer hardware object. In electric motor terms, form factor is the amount of rectified current emitted from a direct current (DC) power source and is expressed as a ratio of the root-mean square (rms) value of the current to the average (av) current or Irms/lav.

In stands for nominal current.

Spikes are large voltage disturbances superimposed onto the normal ac supply with a short duration.

A Slew Rate is the rate at which a UPS can adjust its output frequency in order to synchronise to the frequency of, for example, a standby ac source such as a generator.

A Silicon Avalanche Diode (SAD) a device capable of responding quickly to a high-energy surge or transient and reducing its initial surge current.

Ripple is an AC (alternating current) element superimposed onto the DC (direct current) waveform powering a device.

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