Glossary of Electrical Terms (J - R)

Electrical Terms J - R

Published: Friday, 08 March 2024

Following on from our previous article, covering electrical terms A – I, we will be covering the electrical terms J – R.

This article is not intended to offer electrical installation advice. For any electrical problems or concerns, it is always advisable to seek independent professional assistance from a certified and qualified electrician.


Junction Rectifier

A solid-state device with no moving parts that uses a semiconductor junction to convert alternating current to direct current.



A measurement of power; one kW = 100 Watts.

Kilowatts - hour

A term used to state a unit of electricity utilised during a period of one hour: (kWh)

Light-emitting Diode (LED)

A solid-state device featuring a p-n junction that can produce light when a modest current is applied to it.


An atmospheric electric discharge in the form of a spark or flash; if there is a risk of property damage, the building can be equipped with lightning conductors that safely allow the atmospheric discharge to dissipate to earth. 


A complete lighting unit containing all of the necessary components for installing, housing, connecting, and distributing a light source, such as a bulb or lamp.



A ferromagnetic substance that can maintain a magnetic field around itself. Loadstone is a naturally occurring rock with magnetic properties that can be transmitted to iron and steel. Commercial magnets, on the other hand, are manufactured by placing a suitable metal inside a wire coil that conducts a direct current. 

Mineral-insulated copper cable (MICC) 

A narrow copper tube holding one or more bare copper conductors isolated from one another and the tube carrying them by compressed magnesium oxide, a white powder capable of reaching 10000 degrees Celsius and providing good insulating characteristics when dry.


The smallest part of a substance that can exist without altering shape or form; all matter is composed of molecules, whether solid, liquid, or gas. 


An electro-mechanical mechanism that converts electrical energy into mechanical energy. It typically provides rotational energy to drive a load. 

Mutual Induction

When two coils are near together and an alternating current is passed through one of them, the alternating magnetic field generated by the first coil induces an alternating voltage in the second coil. This effect can be improved by placing the coils on a laminated steel core.


A terminal opposite a positive terminal on a battery or other direct current system to which conventional current flows when a circuit is formed between the battery's positive and negative terminals or another source. Note that electron current flow, or actual current flow in a circuit, is negative to positive. 


In electrical distribution networks, a zero value is referred to as ground. A common point connected to ground via a conductor. 


A word that refers to the core of an atom.


Ohms Law states that when a potential difference of 1 volt is placed across a resistance of 1 ohm in an electrical circuit or component, a current of 1 ampere will flow at a constant temperature. 


An overcurrent is an electric current that exceeds the predicted value in a circuit; it can be caused by an overload, low resistance, or a short circuit.


Parallel paths (PATHS) 

Running side by side; in the event of an electrical ground fault, current may travel from the fault to the supply transformer via two or more paths. The earth connection of the supply system may give one path, while other metallic parts connected to the earth may provide additional paths. 


The phrase used to refer to any live conductor in an alternating current system. The word is commonly used to refer to either single or three phases.

Protective Multiple Earthing (PME)

This is an earthing layout in which the supply system's neutral serves as the primary earth point, ensuring a return path to the distribution supply transformer for any fault current flowing to earth in the installation being supplied. 


The designation of terminals, such as battery-specific conductors in a circuit, or the requirement that single-pole switching devices be situated solely in the line conductor of a single-phase lighting circuit. 


The rate of work is measured in Watts or kilowatts (kW). In a resistive circuit, such as an electric heater, the heater's power rating is proportional to the voltage supplied and the current flowing through it, therefore P = V x I. 

Power Factor (PF) 

In alternating current (ac) inductive or capacitive circuits, the power factor is the ratio of true power to apparent power. 

pf = W/VA or pf = kW/kVA

Protective Multiple Earth (PME)

An earthing system in which many earth points are directly connected to the central neutral point.

Protective Neutral Bonding (PNB)

The intentional connecting of a protective earth conductor and a neutral conductor in an installation. 


In atomic physics, this is a positively charged particle found in an atom's nucleus.


Polyvinyl chloride is a polymer that is commonly used to insulate electrical lines. 

Trainee Electricians


Quantity of Electricity

 The amount of electrical energy flowing across a circuit, which is determined by the current and the time it flows.



A phrase used to describe a circuit that starts at one point but does not return there. A classic example is the (A2) radial socket circuit, in which the conductors end at the final socket outlet. 


A device for converting alternating current (AC) to direct current (DC). The device is made up of one or more diodes that work together to achieve half- or full-wave rectification.

Residual Current Circuit Breaker (RCCB)

This circuit protection device combines the functions of a micro circuit breaker and a residual current circuit breaker into a single small item. RCCBs are typically found in a distribution board or consumer control unit.

Residual Current Device (RCD)

This is a circuit breaker that detects earth leakage by continuously monitoring the flow of electricity into and out of a circuit through the line and neutral. An in-balance of current happens when an earth fault develops or when a person comes into contact with a live conductor in the circuit, and the RCD opens-circuits.


Resistance in a circuit is defined as the opposition to current flow in Ohms (Ω). It can be caused by a purpose-built unit like a heating element or a problem like a loose termination or an underrated wire.


Refers to the rotating portion of an electric motor. The rotor can have a 'cage' design, known as a 'cage rotor', or it can be wound with conductors, known as a 'wound rotor’.

In our next and final article, we will be covering letters S – Z.

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