Last edited 12 Dec 2017

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Glossary of electrical terms


Ampere is a unit of electric current equal to the flow of one coulomb per second.

Approved document R:

Physical infrastructure for high-speed electronic communication networks.

Big Data:

Big Data is both a general term for the expected explosion in data as more interactions take place over the Internet and a more specific term in the information and communications technology (ICT) sector referring to data sets that are too large or too complex to be handled by commonly available software tools.

Central storage:

This is electricity storage, typically consisting of batteries, located centrally on the domestic network normally near the Consumer Unit or included with other centrally located equipment or plant, for example a photovoltaic (PV) inverter.

Centralised inverter:

The term centralised inverter refers to a now outdated practice of connecting more than one PV string in parallel to an inverter. Doing this makes it difficult to optimise the performance of each string and for this reason string inverters (one inverter per string) has become common.

Clean AC (colloquialism):

clean AC is a term referring to a pure sinusoidal waveform. Many power conversion processes typically rely on rapid switching (Pulse Width Modulation) of the electricity which can produce voltage spikes, harmonics and other irregularities. If these are not adequately catered for in the circuit design or device screening it can interfere with radio and TV transmissions or other equipment.

Closed loop:

a closed loop system (simple or complex) is one where the output of a system is sensed and fed back, often as an error signal relative to the input stimuli, to ensure a desired set point (outcome) is achieved.

Consumer Unit:

a piece of equipment located where the incoming mains supply is fed to the individual domestic circuits. It typically includes protection and isolation hardware.

Control scenario:

a control scenario is a set of rules or instructions that guide the system variables to deliver the required outcomes.

Current density:

this is the current density in an electrical conductor measured in A/cm2.


the flow of electricity through a conductor measured in Amps.


this is a general term referring to everything that consumes electricity.


an item that consumes electricity which is primarily electronic in nature (mobile phone, computer, TV etc.) as opposed to an electrical appliance (washing machine, fridge etc.). As more traditional appliances become smart and Internet enabled they too will, in terms of their controllability and system performance, become more like modern electronic devices.

Distributed storage:

this refers to electrical storage, typically consisting of batteries, distributed throughout the domestic network for example, in laptop computers and mobile phones.


light output measured in lumens per watt (lm/W).

Electro-migration (in integrated circuits):

this refers to a phenomenon where the current density in a conductor gets so high that it transports the metal ions along the path of current flow and forms voids at the grain boundaries. When this happens in excess the conductor essentially breaks and the integrated circuit fails. Typically the current density in domestic wiring for example, is several hundred A/cm2 but for integrated circuits it can be as high as 1,000,000 A/cm2 for aluminium interconnects or even higher for copper.

I2R losses:

this is the energy lost (dissipated) in a conductor as a result of Joule heating which increases proportionally to the resistance and as the square of the current flowing.

Information and Communications Technology (ICT):

a broader term than IT (Information Technology) and applies to a more integrated network of communication including computers, telecommunications and associated software.

Imaginary impedance:

in AC circuits a ‘real’ resistive component (found in DC and AC systems) has two other impeding mechanisms referred to as reactive or imaginary components. One is related to the changing magnetic field and self-inductance and the other to electrostatic storage and capacitance.

Inductive coupling:

inductive coupling is where an alternating electromagnetic field induces a current in an adjacent conductor.


a load is a general term for anything that consumes electricity.

LTE networks – LTE (Long Term Evolution):

a wireless broadband technology designed to support Internet roaming and is often referred to as 4G. It supports browsing, VoIP (Voice over Internet Protocol) and other IP based services.


machine-to-machine refers to communications between machines. As ‘things’ become smarter and Internet enabled they will communicate with each other without human intervention – it is closely aligned with the Internet-of-Things (IoT).

Network (the domestic network and the local distribution network (DNO managed)):

a domestic network refers to the cables, connectors and equipment that connect the electricity supply (the meter) to the end device or appliance (load). More recently the domestic network may also consider conversion processes as many of these are now external to the device itself. The local distribution network is that which is operated by the DNO up to and including the meter.

No-load consumption:

this typically refers to the electricity consumed by a power supply or converter when it is not providing any output. Parasitic consumption refers to when a device is on standby mode but is not actually being used, for example a TV. Other examples of hidden energy waste include leaving batteries on charge beyond when they are fully charged.


this refers to a domestic dwelling that is connected to the national 230 V AC supply grid supply.

Open loop:

an open loop system is one where an input stimuli is given to a system that with good design should achieve a certain set point or output. It does not have any error correcting feedback from output to input compensating for system variations.


a Piconet is a very local network between for example, a mobile phone and a computer, usually wireless.

Power Usage Effectiveness (PUE):

a measure of the power used by the computing equipment in a Data Centre compared to the total Data Centre demand. A PUE of 2 means that half of the total power supplied to the Data Centre (including cooling, lighting, fans etc.) is used by the computing equipment; ideally it should be 1.

Protected circuit.

An electrical circuit protected against fire.

Pulse Width Modulation (PWM):

the simplest way to think of this is the time a switch is on. If a switch is on for a long time current flows for the majority of the time. If it is only on for a very short period then little flows. Generally, in electrical circuits the switch is electronic and may operate at about 500 kHz or every several microseconds.

String (PV):

a string is where a number of PV panels are connected in series. For a typical domestic installation this is normally in the region of 8 to 16 panels.


a general term referring to everything related to the generation, transmission and distribution of electricity up to and including the domestic meter.


a system means a number of devices and appliances (loads) connected to an electricity supply (local or national) via a network.

System performance:

this refers to how the complete domestic electricity system works in harmony to deliver a final desired outcome at any moment in time.


a three-phase system is where three alternating currents are carried by three separate conductors each of which reach their instantaneous peak 120 degrees apart.

Unit of electricity:

electricity consumption is typically measured in kWh or multiples thereof and this is the unit normally used for domestic pricing.


an electromotive force or potential difference measured in Volts.


a Watt is a measure of power and is equivalent to one Joule per Second corresponding to the rate of consumption in a circuit where the potential difference is one Volt and a current of one Ampere flows.

This article was created by --BRE. It was taken from The future of electricity in domestic buildings, a review, by Andrew Williams, published in November 2014.