Electrical Schematic Symbols With Explanation at a Glance

An effective way of understanding the electrical systems or connections among the diverse equipment utilizes the standard schematic symbols. Single line or online electrical diagrams uses these schematic symbols to indicate the paths and components of an electrical circuit.  A single line diagram shows the distribution path from main incoming source to the downstream load by indicating equipment and devices with standard symbols.

There are several national and international standard associations for schematic symbols like International Electro-technical Commission (IEC), Institute of Electrical and Electronics Engineers (IEEE), National Electrical Manufacturers Association (NEEMA), etc. Symbols for the corresponding device will vary depend on the standardized association.

Some of those symbols used in the fields like wiring, metering, exciting sources etc are discussed below:-

1. Electrical wiring

Terminal marking and wiring connection diagrams are helpful mainly in troubleshooting process while tracing the wires and making connection to the devices. Some of the wiring symbols are given below which are used for showing the electrical connection between the diverse devices or machines in an electric circuit.

Bold line indicates the power connection to various powered devices while thin line indicates the control connections which are of low power or signal level connectors. Junction or small dot between the several connections shows the connection active state. Fuse, distribution board and other symbols comes under the schematic wiring symbols.

2. Metering Equipment

Indicating meters are used to display the parameter like voltage, current, power, frequency, etc. and while drawing the wiring connection, these schematic symbols resembles the physical connection of the indicating meters.

These meters include AC, DC meters , Frequency meters for the frequency, tachometers to indicate the speed of the motors, energy or watt-hour meter to indicate the energy consumed, synchro scope to indicate the phase sequence and VAR meter to indicate the reactive power.

3. Different Sources

There are two types of sources, AC and DC. Again AC supply might be single phase or three phase supply. DC source is indicated by the battery or some signal level sources like Vcc, Vdd and those symbols are listed below. Voltage sources include exponential, triangular and bipolar voltages sources and so are the current sources. These schematic symbols are mainly used to indicate the source which excites the corresponding circuit. Due to this schematic way of representation, one can easily understand the nature of the supply given to the circuit.

Along with the sources, grounding to the circuit provides the return path for the supply and also provides the safety to the equipments used in case of the faults that occur in the electrical system. Analog and circuit ground symbols are given below, indicating the earth terminal. Similarly chassis ground indicates the equipment earthing against fault conditions.

4. Switches

Switches are mainly used to make or break electrical circuits under normal and abnormal conditions. These might be automatic or manual. Differentiation of these switches depends on several factors like number of poles used, operating conditions and time required to switch the circuit, etc.

Some of these are given below.

These includes single pole single throw switch (SPST), double pole double throw switch (DPDT) which are based on the number of circuits to be switched ON at a time. Schematic symbols for limit switch, proximity switch, fuse, spring based switch and etc are shown below.

5. Electromechanical Devices

Electromechanical devices include generators, motors, turbines, etc. Transformers come under electrostatic devices that can be single phase, three phase, variable type, star/delta, current or auto transformers used for changing the level of the voltage or current.

Appropriate schematic symbols as given below:

Type of generator (motor) depends on the nature of voltage supplied by the device (voltage supplied to). In generator mechanical energy is converted to electrical. It can be DC or AC depending on the type of generator. Similarly motor can also be DC or AC. Symbols for different motors, generators, type of winding and turbine are shown above.

6. Different Components

These are also called passive components. Many of the electrical and electronic circuits comprise these basic components. These are resistors, inductors and capacitors.

Resistors:

A resistor offers the resistance to the current flow. These are used for current limiting operations. The resistance value of the resistor may be fixed or variable or light dependent types.

Inductors:

Inductor opposes the change in the current flow and stores the energy in form of the magnetic field. Type of inductor depends on several factors like core used, variable or fixed value, etc. Some of the symbols for this passive component is shown below.

Capacitors:

Capacitor blocks DC and allows AC and does the functions like filtration, storing of the energy, etc. These are of types like polarized, non polarized and variable.

7. Indicators

Schematic symbols for some of the indicators or output devices like pilot lamps, loud speakers, buzzer and bells are given below which are used for producing alarms in the electrical circuits.

Hope that you have observed the schematic symbols for some of the devices. We know the importance of single line or online diagrams for the different electrical connection especially at the time of trouble shooting and learning as newly placed person.

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Photo Credit:

• Switches1 by edrawsoft
• Switches2 by edrawsoft
• Various inductors by g3npf
• Different Capacitors by eng.cam