Capacitor Symbol
Definition: The Capacitor symbol represents a passive two-terminal component that stores electrical energy in an electric field, drawn as two parallel lines (non-polarised) or one straight line and one curved line (polarised/electrolytic) per IEC 60617-04 and ANSI Y32.2 / IEEE 315-1975, with capacitance measured in farads (F); it is assigned the schematic designator C.
Also known as: capacitor symbol, cap symbol schematic, condenser symbol, C symbol circuit diagram, electrolytic capacitor symbol, polarised capacitor symbol.
What the Capacitor symbol means
The capacitor symbol denotes a component that accumulates and releases electric charge, blocking direct current (DC) while allowing alternating current (AC) to pass — a property exploited in filtering, coupling, and timing circuits. The two plates of the symbol represent the two conductive electrodes separated by an insulating dielectric, which is the physical structure that stores energy as charge (Q = C × V).
In a schematic, the capacitor symbol communicates both the presence of energy storage and, by its variant form, whether the component has polarity. A flat-plate symbol signals a non-polarised ceramic or film capacitor that can be connected in either orientation; a curved-plate or '+' marked symbol signals a polarised electrolytic or tantalum capacitor that must be connected with the positive terminal (pin '+', id 'pos') toward the higher potential, and the negative terminal (pin '-', id 'neg') toward the lower. Reversing a polarised capacitor can cause it to fail, vent, or rupture.
How to identify the Capacitor symbol
The standard non-polarised capacitor symbol consists of two short parallel lines (representing the two capacitor plates) positioned perpendicular to and centred on the connecting lead lines — giving the appearance of a gap between two parallel bars. In IEC 60617-04, both lines are straight and equal. In ANSI Y32.2 / IEEE 315-1975, the same two-parallel-lines form is used for non-polarised types; the polarised (electrolytic) variant has one plate drawn as an arc or curved line (the negative plate) facing away from the positive plate. A '+' sign is often added beside the positive plate to mark polarity. The overall symbol is small and symmetrical about the lead axis, making it instantly distinguishable from the resistor rectangle or the coil loops of an inductor.
Function in a circuit
A capacitor stores energy in the electric field between two conductive plates separated by a dielectric insulator. When a voltage is applied, charge accumulates on the plates (Q = C × V); when the source is removed, the capacitor discharges that stored energy back into the circuit. Capacitors block DC (once fully charged, no DC current flows) while passing AC signals, making them essential for power-supply filtering to smooth ripple voltage, signal coupling between amplifier stages without transferring DC bias, frequency-selective filtering in RC and LC circuits, and timing in oscillator and delay circuits.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617-04 defines the non-polarised capacitor as two parallel straight lines with connecting leads perpendicular to the plates; the polarised (electrolytic) capacitor is shown with one plate as a straight line marked '+' and the other as a straight line (some regional interpretations use a curved line for the negative plate, but IEC 60617 itself uses straight lines with a '+' mark). |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2-1975 / IEEE 315-1975 defines the non-polarised capacitor identically to IEC (two parallel lines). The polarised electrolytic capacitor in ANSI / IEEE 315 is traditionally shown with one plate curved (the negative plate) and one straight (the positive plate), with a '+' marker on the positive side. |
| Key difference | For non-polarised capacitors, IEC 60617 and ANSI Y32.2 / IEEE 315 symbols are effectively identical (two parallel lines). For polarised (electrolytic) capacitors, ANSI / IEEE schematics commonly use a curved negative plate; IEC schematics use two straight lines with a '+' polarity marker. In practice many CAD tools blend both conventions, so the '+' marker is the most reliable polarity indicator regardless of standard. |
Terminals / pins
| Pin | Name |
|---|---|
| pos | + |
| neg | - |
Typical values
Capacitance is measured in farads (F); practical components range from picofarads (pF, 10⁻¹² F) for small ceramic capacitors used in RF circuits, through nanofarads (nF, 10⁻⁹ F) for film and ceramic types used in timing and filtering, to microfarads (µF, 10⁻⁶ F) for electrolytic capacitors used in power-supply filtering, up to farads (F) for supercapacitors / ultracapacitors used in energy storage. Common working voltage ratings are 6.3 V, 10 V, 16 V, 25 V, 35 V, 50 V, 63 V, 100 V, 250 V, and 450 V for electrolytic types. Tolerance classes include ±5 %, ±10 %, ±20 %, and for precision film types ±1 % or ±2 %.
Where the Capacitor symbol is used
- Power-supply decoupling: 100 nF ceramic capacitors placed close to every IC power pin to suppress high-frequency switching noise
- Bulk filtering: 100 µF – 4700 µF electrolytic capacitors across power-supply rails to smooth rectified DC voltage ripple
- AC coupling (blocking capacitors): series capacitors between amplifier stages to pass AC signals while blocking DC bias offsets
- RC timing circuits: a capacitor charging through a resistor sets the time constant τ = RC in oscillators, timers (e.g. 555 timer), and delay circuits
- Resonant LC filters and tuning circuits in radio-frequency (RF) and audio applications
- Motor start / run capacitors in single-phase AC induction motors to create a phase-shifted starting torque
Example
In a 5 V USB-powered microcontroller circuit, a 100 nF ceramic capacitor (C1) and a 10 µF electrolytic capacitor (C2) are placed in parallel directly across the VCC and GND pins of the MCU. The non-polarised capacitor symbol for C1 (two parallel straight lines) and the polarised symbol for C2 (one straight line marked '+' connected to VCC, one curved line to GND) appear side by side on the schematic. Together they filter both high-frequency digital switching noise and lower-frequency power-supply fluctuations, preventing voltage glitches that would cause the microcontroller to reset.
Key facts
- The capacitor symbol is two parallel lines in IEC 60617-04 and ANSI Y32.2 / IEEE 315-1975; the polarised (electrolytic) variant adds a '+' marker or curves the negative plate to indicate polarity.
- The schematic designator for a capacitor is C; individual capacitors are labelled C1, C2, C3 … in sequence, as defined in IEEE 315-1975.
- Capacitance is measured in farads (F); practical values range from picofarads (pF) in RF circuits to farads (F) in supercapacitors, with microfarads (µF) the most common unit in general electronics.
- A capacitor has two terminals: positive (pin id 'pos', marked '+') and negative (pin id 'neg', marked '-'); polarised types — electrolytic and tantalum — must be connected with the positive terminal at the higher potential or they risk failure.
- A capacitor blocks direct current (DC) once fully charged and passes alternating current (AC), making it the fundamental component for decoupling, filtering, and AC signal coupling in circuits.
- The energy stored in a capacitor is E = ½ × C × V² (joules), where C is capacitance in farads and V is voltage across the plates.
- Non-polarised capacitors (ceramic, film, mica) can be connected in either orientation; polarised capacitors (electrolytic, tantalum) have a defined positive and negative terminal and will be damaged or destroyed if reverse-biased.
- IEC 60617-04 is the international standard defining the capacitor symbol; ANSI Y32.2-1975 / IEEE 315-1975 is the North American equivalent.
Diagrams that use this symbol
- electrical line diagram
- bridge rectifier circuit diagram
- fan connection with capacitor
- electric motor diagram
- simple motor diagram
- single phase motor wiring diagram
- single phase motor connection diagram
- 1 phase motor connection
Frequently asked questions
What does the capacitor symbol look like?
The standard (non-polarised) capacitor symbol looks like two short parallel lines perpendicular to the connecting wire — like a narrow gap between two bars. The polarised electrolytic capacitor symbol has one straight plate marked '+' and one curved plate (in ANSI / IEEE schematics) or two straight plates with a '+' marker (in IEC schematics). Both versions clearly show the two-plate structure of the physical component.
What does the capacitor symbol mean in a circuit diagram?
The capacitor symbol means that a component at that location stores electric charge and blocks DC while passing AC. The value beside the symbol (e.g. '100 µF') gives the capacitance; a voltage rating (e.g. '25 V') may also be shown. The symbol tells the reader that this node participates in filtering, timing, coupling, or energy-storage functions depending on circuit context.
What is the difference between the IEC and ANSI capacitor symbols?
For non-polarised capacitors, the IEC 60617 and ANSI Y32.2 / IEEE 315 symbols are identical — two parallel straight lines. For polarised electrolytic capacitors, ANSI / IEEE 315 schematics traditionally show one curved plate (negative side) and one straight plate (positive side), while IEC 60617 uses two straight lines with a '+' polarity marker. The '+' marker is the safest way to identify the positive terminal in any standard.
How do I identify the positive and negative terminals on the capacitor symbol?
On the capacitor symbol, the positive terminal (pin id 'pos') is marked with a '+' sign adjacent to the corresponding plate line. The negative terminal (pin id 'neg') is the other plate, sometimes drawn as a curved line in ANSI-style schematics. On physical electrolytic capacitors, the negative lead is marked with a stripe and is typically the shorter lead on new components.
What letter designates a capacitor on a schematic?
The designator letter for a capacitor is C, as defined in IEEE 315-1975 and IEC 60617-04. Capacitors are numbered sequentially on a schematic: C1, C2, C3. The designator appears next to the symbol and in the bill of materials.
What unit is capacitance measured in?
Capacitance is measured in farads (F), an SI unit named after physicist Michael Faraday. Practical capacitor values are expressed in microfarads (µF = 10⁻⁶ F), nanofarads (nF = 10⁻⁹ F), or picofarads (pF = 10⁻¹² F). A '100µF 25V' annotation on the capacitor symbol means 100 microfarads capacitance with a 25-volt maximum working voltage.
What is the difference between a polarised and non-polarised capacitor symbol?
A non-polarised capacitor symbol has two identical parallel lines and no polarity markers — the component can be connected in either direction. A polarised capacitor symbol adds a '+' sign to one plate (the anode) or draws one plate as a curved line; this type — typically aluminium electrolytic or tantalum — must be installed with the '+' terminal connected to the higher-voltage net, or it will fail.
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