This article was automatically translated from the original Turkish version.
An electric circuit is a system formed by connecting various circuit elements—such as resistors, capacitors, inductors, transistors, diodes, and integrated circuits—in a specific arrangement to ensure that electric current follows a defined path in a controlled manner. These systems enable the transmission, conversion, and, when necessary, control of electrical energy from a source to a target point. Fundamentally, an electric circuit involves the regulation of the phenomenon of electricity, which arises from the movement of charged particles—particularly free electrons—along a conductive path.
All electrical devices obtain the energy they require to operate through an electric circuit. A circuit is designed to draw energy from a source—such as a battery, generator, or utility grid—and deliver it to a load—such as a light bulb, motor, or heater—to perform work. This process is based on fundamental principles that enable the transmission and utilization of electrical energy. The structure of circuits varies depending on the type of components used, their connection configuration, and the intended function of the circuit. Current management encompasses the techniques, control methods, and protective mechanisms employed to ensure that energy flows safely, efficiently, and controllably within the circuit. In this context, fuses, circuit breakers, voltage regulators, and current limiters play vital roles.
To understand the operating principle of an electric circuit, certain fundamental concepts must be known. These concepts explain how energy flows within a circuit and how circuit elements behave.
Voltage (Potential Difference): It represents the electrical potential difference between two points. This driving force that causes electrons to move along a conductor is measured in volts (V). Voltage is the essential condition for current to flow; without voltage, no current exists. Sources such as batteries, generators, transformers, or adapters can provide voltage. The magnitude of voltage directly affects the current potential along the same conductor.
Current: It is the amount of electric charge passing through a conductor over a specific period and is measured in amperes (A). The direction and magnitude of current depend on the voltage in the circuit and the electrical properties of the circuit elements. In direct current (DC) systems, current flows in one direction only; in alternating current (AC) systems, its direction changes periodically.
Resistance and Impedance: Resistance is the constant opposition a material offers to the flow of electric current and is measured in ohms (Ω). According to Ohm’s Law, current is directly proportional to voltage and inversely proportional to resistance. In AC circuits, in addition to resistance, reactive components such as capacitors and inductors introduce frequency-dependent oppositions. This combined effect is called impedance (Z). Impedance includes both resistance and reactive components (capacitive and inductive reactance) and is one of the fundamental parameters in AC circuit analysis.
Conductive and Insulating Materials: Materials that conduct electricity well—that is, those with a high density of free electrons—are called conductors (for example, copper, silver, aluminum). Materials that exhibit high resistance to electric current flow and contain no free electrons are classified as insulators (for example, plastic, rubber, glass). Conductors are used in circuits to carry current, while insulators are used to ensure safety and prevent energy loss.
These fundamental concepts are essential for understanding the operating logic of electric circuits and applying current management techniques. In modern electrical and electronic systems, proper current management is critical for increasing efficiency, preventing overloads, maintaining energy quality, and extending device lifespan.
Electric circuits consist of various interconnected elements designed to perform specific functions. These elements enable the transmission of energy, processing of signals, and execution of specific electrical functions. Generally, they are classified into four main categories based on their electrical behavior: active or passive, and linear or nonlinear.
Active elements are components that can supply energy to a circuit or amplify an existing signal. These elements either generate electrical energy directly or control signals to enable specific functions. Examples include generators, batteries, operational amplifiers (Op-Amps), and transistors.
Power Sources: Components such as batteries, generators, and adapters supply the necessary energy to the circuit.
Operational Amplifiers (Op-Amp): These are high-gain integrated circuits with inverting and non-inverting inputs. They are widely used in analog signal processing, filters, summing circuits, and differentiation circuits.
Passive elements cannot generate energy; instead, they consume, store, or distribute energy in a specific manner. Resistors, capacitors, and inductors are the fundamental passive circuit elements. Passive elements regulate the current-voltage relationships in a circuit to ensure system stability and functionality.
Resistors: Used to limit the magnitude of electric current, divide voltage, or create a specific load. They dissipate energy as heat and are measured in ohms (Ω).
Capacitors: Consist of two conductive plates separated by an insulating material. They store electrical energy in an electric field. In alternating current (AC) circuits, they create a phase difference between current and voltage, and their impedance is inversely proportional to frequency.
Inductors (Coils): Formed by winding a conductive wire into a spiral. They store electrical energy in a magnetic field and oppose changes in current. Their impedance is directly proportional to frequency.
Circuit elements can be classified as linear or nonlinear based on their electrical behavior.
The foundation of modern electronic technology lies in semiconductor elements. These components are typically used for switching, signal amplification, or rectification functions.
Diodes: Two-terminal devices (anode and cathode) that allow current to flow in only one direction. They conduct under forward bias and block current under reverse bias. The typical threshold voltage for silicon diodes is approximately 0.7 V. Special types include:
Transistors: Three-terminal semiconductor devices that can control a larger output current using a small input current or voltage.
Electric circuits are classified according to the type of current used and the configuration of circuit elements. This classification is fundamental to determining the operating principles and analysis methods of circuits.
Direct Current (DC) circuits are systems in which the direction of current does not change over time. In these circuits, the current flowing through the load is unidirectional and is typically supplied by sources such as batteries, accumulators, or DC generators. Examples include electronic devices, LED lighting systems, and low-voltage control circuits.
In Alternating Current (AC) circuits, both the direction and magnitude of current vary periodically. Mains electricity is usually supplied in AC form at frequencies of 50 Hz or 60 Hz. Analysis of AC circuits requires consideration of additional parameters such as frequency, phase angle, and harmonics. Therefore, AC systems are typically analyzed using phasors, complex numbers, and the concept of impedance.
In a series connection, circuit elements are connected end-to-end, sharing a single current path. The current through all elements is identical, and the total resistance or impedance equals the sum of the individual values. This configuration is preferred when current must pass through all elements.
In a parallel connection, elements are connected between the same two nodes, and the current through each element divides according to its electrical properties. The voltage across each parallel branch is equal, while the total current equals the sum of the branch currents. This configuration is used when independent operation of loads is desired.
Different analysis techniques have been developed to solve complex electric circuits.
Safe, efficient, and stable operation of electric circuits is possible through proper current management, rapid detection of abnormalities, and the application of appropriate protective measures against potential fault conditions.
A short circuit occurs when conductors that should not be in contact under normal operating conditions form a low-impedance connection. This may result from insulation failures, mechanical damage, incorrect connections, or excessive voltage. Such conditions cause extremely high-amplitude currents to develop in a very short time. Consequently, serious hazards such as excessive heating of conductors, insulation breakdown, mechanical deformation, fire, or explosion may occur.
In three-phase systems, short circuits can appear in different forms: symmetrical (all three phases short-circuited simultaneously), phase-to-phase, and phase-to-ground. Two key quantities are considered in protection design:
Circuit Breakers: Switching devices that automatically open the circuit under conditions of overcurrent, short circuit, or ground fault. In industrial facilities, Air Circuit Breakers (ACB) are frequently preferred due to their high current capacity and advanced protection functions. Arc-extinguishing chambers allow safe interruption of high currents. Two important technical parameters in circuit breakers are:
Contactors: Electromechanical switches used primarily for remote control of high-current loads (such as motors and large heaters). When the coil is energized, the resulting magnetic field closes the contacts. DC contactors are designed to reduce the risk of arcing in DC circuits and play a vital role in the safe management of high DC currents in energy storage systems, electric vehicles, and photovoltaic energy systems.
Earthing is the process of electrically connecting the conductive parts of electrical equipment to the earth to ensure safety, reduce the risk of electric shock, and eliminate hazardous voltages during fault conditions. In electrical engineering practice, earthing is not only critical for human safety but also for equipment protection, system stability, and reduction of electromagnetic interference.
The primary objective is to safely direct any voltage that may develop on conductive enclosures due to faulty operation or insulation failure, through a low-impedance path to the earth. This prevents leakage currents from passing through the human body, avoids excessive voltage buildup in system components, and ensures rapid triggering of protective devices (fuses, circuit breakers, RCDs).
In designing earthing systems, factors such as soil resistivity (Ω·m), dimensions and layout of earth electrodes, and connection methods are considered. Maintaining earthing resistance at the lowest possible level enhances protection effectiveness. IEC 60364 and national standards define acceptable maximum earthing resistance values. The main types of earthing are:
The connection of conductive enclosures of electrical devices to earth. The purpose is to prevent dangerous voltages from appearing on enclosures during insulation failure. Industrial machinery, distribution panels, metal-enclosed equipment, and household electrical appliances are connected to this type of earthing.
The connection of specific points of the electrical system—such as the neutral point of a generator or transformer—to earth, as required by operational conditions. This method ensures that the system’s voltage levels remain balanced with respect to a reference point.
A type of earthing used to improve the operational performance of electrical devices, reduce signal noise, or ensure electromagnetic compatibility. It is applied in communication systems, data centers, and measurement instruments to maintain signal integrity.
Residual Current Devices (RCDs) are safety devices that continuously monitor the current values in the phase and neutral conductors of an electric circuit. They detect any difference between these two values and automatically open the circuit if the difference exceeds a predetermined threshold.
The operating principle is based on the requirement that the sum of the phase and neutral currents passing through a differential current transformer connected in series with the circuit must be zero. A leakage current arises when a portion of the current returning from the load flows back through an earth path. This imbalance creates a magnetic imbalance in the transformer’s secondary winding, triggering the mechanism. Typical applications include:
RCDs are installed in designated areas in industrial facilities, office buildings, and residential premises according to standards. However, selecting the correct type (AC, A, F, B) is essential to prevent false tripping caused by motor loads, harmonic currents, or capacitive leakage currents.
Selectivity is the principle that, in the event of a fault in an electrical system, only the protective device located in the affected section should operate, while other sections continue to function. This approach is essential for maintaining energy continuity and minimizing the impact of faults on the rest of the system.
Selectivity is applied in three main ways:
Selectivity principles are mandatory in structures where energy continuity is critical, such as hospitals, data centers, and manufacturing plants. During implementation, manufacturers’ selectivity tables and coordination diagrams are taken into account.
Basic Electrical Concepts
Electrical Circuit Elements
Active Circuit Elements
Passive Circuit Elements
Linear and Nonlinear Elements
Semiconductor Circuit Elements
Circuit Types and Analysis
Direct Current (DC) and Alternating Current (AC) Circuits
Series and Parallel Connections
Circuit Analysis Methods
Current Management and Protection Mechanisms
Short Circuit and Overcurrent
Protection Devices
Earthing Systems in Electric Circuits
Protective Earthing (PE)
Operational Earthing
Functional Earthing
Residual Current Devices (RCD)
Principles of Selectivity