Varistor (MOV) Symbol
Definition: The Varistor (MOV) symbol represents a voltage-dependent, nonlinear resistor — most commonly a Metal Oxide Varistor (MOV) — defined in IEC 60617 and recognised in ANSI Y32.2 / IEEE 315 as a two-terminal passive protection device whose resistance decreases sharply when the applied voltage exceeds its clamping voltage, diverting transient surge energy away from sensitive circuit components.
Also known as: MOV, Metal Oxide Varistor, voltage-dependent resistor, VDR, surge suppressor, transient voltage suppressor (TVS varistor).
What the Varistor (MOV) symbol means
The Varistor symbol denotes a two-terminal, bidirectional, nonlinear resistive device that exhibits a high impedance under normal operating voltages and a low impedance (clamping) condition when the voltage across it exceeds the device's varistor voltage (V_N). The transition is governed by the exponential V-I characteristic of the zinc oxide (ZnO) granule matrix used in Metal Oxide Varistors, giving the device a nonlinear resistance that falls from megaohms at normal voltage to a few ohms during a surge event.
In schematics, the Varistor symbol appears in parallel with the circuit or component being protected — across power supply rails, at AC mains inputs, and on signal lines subject to electrostatic discharge or lightning-induced transients. The device clamps transient voltages to a safe level by absorbing surge energy as heat, protecting downstream components from overvoltage damage. The reference designator RV (for a varistor) or MOV is printed next to the symbol.
How to identify the Varistor (MOV) symbol
The Varistor symbol is drawn as a resistor rectangle (IEC style) or zigzag resistor (ANSI style) with a diagonal arrow or slash drawn through the body, indicating the variable (nonlinear) resistance characteristic. In IEC 60617, the varistor uses the general variable-resistor symbol modified with a 'U' or arc overlay to indicate voltage-dependent operation; a letter 'V' inside or adjacent to the symbol is sometimes used. Some standards show a small 'U' shape inside the resistor rectangle to denote the nonlinear characteristic. The symbol is non-polarised — the two terminals A and B are interchangeable.
Function in a circuit
In a circuit, the Varistor (MOV) functions as a transient overvoltage clamp connected in parallel with the protected load or supply rail. Under normal operating conditions the varistor presents a very high impedance (typically >1 MΩ) and draws negligible current, behaving as an open circuit. When a voltage surge or spike exceeds the clamping voltage (e.g. 275 V for a 130 V_AC-rated MOV), the varistor resistance drops dramatically, diverting the surge current through itself and limiting the voltage across the protected circuit to the clamping voltage level. The varistor absorbs the surge energy (rated in joules) and returns to its high-impedance state after the transient subsides.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617-04 (passive components) defines the varistor symbol as a resistor rectangle with a modifier indicating nonlinear voltage-dependent resistance. IEC 61051 specifically covers varistors for use in electronics, defining electrical characteristics and test methods. |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2-1975 / IEEE 315-1975 represents the varistor using the zigzag resistor glyph with a diagonal arrow through it (the same modifier used for a variable resistor), with 'V' indicating the voltage-dependent characteristic. The reference designator RV is specified for varistors. |
| Key difference | IEC uses a filled rectangle as the base resistor body; ANSI uses a zigzag line. Both standards then apply the same diagonal arrow modifier to indicate the variable nonlinear resistance. The functional meaning is identical. |
Terminals / pins
| Pin | Name |
|---|---|
| a | A |
| b | B |
Typical values
Varistor voltage V_N (at 1 mA): 11 V to 1000 V. Maximum continuous operating voltage V_AC: 11 V to 750 V RMS. Energy absorption (single pulse, 2 ms): 0.1 J to 6000 J. Peak surge current (8/20 µs pulse): 100 A to 70,000 A. Clamping voltage at peak surge: 1.5 × to 3 × V_N typical. Capacitance: 10 pF to 20,000 pF.
Where the Varistor (MOV) symbol is used
- AC mains power supply surge protection — a 275 V_AC MOV placed across the live and neutral input terminals of power supplies and appliances
- Protecting relay coils and inductive loads from back-EMF voltage spikes when switched off
- Motor starter and industrial drive circuits to suppress transients on contactor switching
- Telephone and data line protection against lightning-induced transients (lower-voltage varistors on signal lines)
- Surge protection devices (SPDs) for electrical distribution panels (IEC 61643-11 / UL 1449)
- Protecting semiconductor components in power converter circuits from switch-node voltage overshoot
- Automotive electronics protection against load-dump transients on the 12 V vehicle bus
Example
In a household appliance power supply schematic, a 275 V_AC Metal Oxide Varistor (e.g. Bourns MOV-14D271K) appears in parallel with the AC mains input, between the live (L) and neutral (N) lines, upstream of the fuse and rectifier bridge. The varistor symbol is drawn across the L and N rails. During a lightning-coupled surge on the mains, the MOV clamps the transient to approximately 710 V peak, absorbing the surge energy and protecting the rectifier diodes and filter capacitors downstream.
Key facts
- A Varistor (MOV) is a voltage-dependent nonlinear resistor whose resistance decreases from megaohms to milliohms when the applied voltage exceeds its clamping voltage, absorbing transient surge energy to protect circuit components.
- The Varistor symbol is a resistor symbol (rectangle in IEC, zigzag in ANSI) with a diagonal arrow or slash through the body, indicating nonlinear variable resistance; it is non-polarised and bidirectional.
- The standard reference designator for a varistor is RV per IEEE 315-1975; MOV is also widely used as a part-type identifier in schematics.
- Metal Oxide Varistors (MOVs) are manufactured from compressed zinc oxide (ZnO) granules with small amounts of bismuth, cobalt, and other metal oxides; the grain boundary junctions create the nonlinear V-I characteristic.
- The varistor voltage V_N is defined at 1 mA DC; a 275 V_AC-rated MOV has a V_N of approximately 390–430 V DC, and a clamping voltage of approximately 710–750 V at an 8/20 µs surge pulse.
- Varistors degrade with repeated surge events — each surge permanently reduces the varistor's energy handling capacity; severely degraded MOVs can fail short-circuit, which is why a series fuse or thermal fuse is required in mains applications.
- IEC 60617-04 defines the varistor as a passive component symbol; IEC 61051-1 and IEC 61051-2 govern varistor specifications and test methods for use in electronics.
Frequently asked questions
What does the varistor symbol look like in a schematic?
The varistor symbol is drawn as a standard resistor shape — a filled rectangle in IEC style or a zigzag line in ANSI style — with a diagonal arrow or slash drawn through the body. This modifier indicates the voltage-dependent nonlinear resistance. The symbol is non-polarised, so either terminal can be connected to either circuit node.
What does the varistor (MOV) symbol mean in a circuit diagram?
The varistor symbol means a nonlinear overvoltage protection device is connected in parallel with the protected circuit. It indicates the presence of a component that clamps voltage transients by dramatically reducing its resistance when the applied voltage exceeds the clamping threshold, absorbing surge energy.
What is the difference between a varistor and a Zener diode in a schematic?
A Zener diode symbol shows a diode with bent cathode ends and is polarised (unidirectional clamping). A varistor symbol is a modified resistor and is non-polarised (bidirectional clamping). Varistors handle much larger surge energies (joules vs millijoules) and are preferred for mains-level surge protection; Zener diodes are used for precision low-voltage regulation.
What is the designator letter for a varistor?
The standard IEEE 315 reference designator for a varistor is RV. In practice, schematics also label varistors as MOV (Metal Oxide Varistor) or VDR (Voltage Dependent Resistor) adjacent to the symbol, depending on the schematic software and design convention used.
What standard defines the varistor schematic symbol?
The varistor symbol is defined in IEC 60617-04 (passive components) as a resistor symbol with a nonlinear modifier. ANSI Y32.2 / IEEE 315-1975 uses the same variable-resistor arrow modifier on a zigzag resistor body. IEC 61051 covers varistor product specifications and testing.
Is the varistor symbol polarised?
No. The varistor symbol has no polarity — both terminals are interchangeable. Metal Oxide Varistors are symmetrical, bidirectional devices that clamp positive and negative voltage transients equally. This is shown in the symbol by the absence of any arrow, dot, or + sign indicating a positive terminal.
What voltage rating do I look for when reading a varistor symbol?
The varistor is labelled with its maximum continuous working voltage (V_AC or V_DC), its varistor voltage V_N, and its energy rating in joules. For a typical 230 V AC mains application a 275 V_AC or 300 V_AC rated MOV is used. The label appears next to the RV designator in the schematic.
Place the Varistor (MOV) symbol on a wiring diagram or schematic in the free online circuit diagram maker — no download required.