Ammeter Symbol
Definition: The Ammeter symbol represents a current-measuring instrument inserted in series with a circuit to indicate the magnitude of electric current flowing through that branch, shown in circuit diagrams as a circle containing the letter 'A', with two terminals (In and Out) denoting the series current path, as standardised in IEC 60617-08 and ANSI Y32.2 / IEEE 315-1975 for measuring instrument symbols.
Also known as: ammeter symbol, ampere meter, current meter symbol, amperemeter, amp meter, galvanometer (sensitive variant), milliammeter, microammeter.
What the Ammeter symbol means
The Ammeter symbol marks the point in a circuit where current magnitude is being measured. Because current is measured in series, the Ammeter symbol appears as an element inserted along a conductor path, not between two nodes in parallel. The 'A' inside the circle identifies the quantity being measured (current in amperes, A), and the two terminals (In and Out) carry the full circuit current through the instrument.
In practical schematics and wiring diagrams the Ammeter symbol represents any device that measures current — from a bench instrument (analog moving-coil or digital multimeter in current mode) to a fixed panel meter, clamp meter, or current transducer. In power and industrial diagrams the ammeter is commonly shown on the output of generators, motors, and transformers to provide operating current monitoring.
How to identify the Ammeter symbol
The Ammeter symbol is drawn as a circle with the capital letter 'A' printed inside. Two conductor lines enter and exit the circle at opposite sides (typically left and right, representing In and Out), indicating the series connection in the measured circuit. Some schematic styles show a small plus (+) sign at the In terminal to indicate the conventional current entry direction for polarity-sensitive (DC) instruments. In power system one-line diagrams, the ammeter symbol may be accompanied by a current transformer (CT) symbol indicating indirect measurement through a step-down CT.
Function in a circuit
An ammeter measures the electric current flowing through it by converting the current signal into a readable indication. In analog moving-coil instruments, the measured current passes through a low-resistance shunt; a small fraction of the current deflects a coil in a magnetic field, moving a pointer proportional to the current magnitude. Digital ammeters use a precision shunt resistor and measure the voltage drop (V = I × R_shunt) with an ADC. The internal resistance of an ideal ammeter is zero ohms; practical ammeters have very low resistance (milliohms to fractions of an ohm) to minimise the voltage burden (voltage drop) across the measurement point.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617-08 defines the measuring instrument symbol as a circle with the measured quantity abbreviation inside. The ammeter symbol is a circle with 'A' per IEC 60617-08 (instruments and signal sources). Ammeter performance standards are covered by IEC 61010-1 (safety) and IEC 61557 (electrical safety measurement instruments). |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2 / IEEE 315-1975 defines the ammeter symbol identically: a circle with 'A' inside, with two series connection points. The reference designator for an ammeter is typically 'A' (for instruments) or 'M' in some conventions. |
| Key difference | IEC 60617-08 and ANSI Y32.2 / IEEE 315-1975 define the same circle-with-letter ammeter symbol. The representations are identical in both standards; no visual difference exists. IEC adds specific qualifier symbols for instrument types (rectifier, thermal, electrodynamic) inside the circle when needed. |
Terminals / pins
| Pin | Name |
|---|---|
| in | In |
| out | Out |
Typical values
Panel meters: 0–1A, 0–5A, 0–10A, 0–100A ranges (direct connection); 0–5A secondary (with CT for higher currents up to thousands of amps). Accuracy classes: IEC 60051: Class 0.5, 1.0, 1.5, 2.5, 5. Digital multimeter ammeter mode: mA range (200mA with ~1Ω input resistance), A range (10A with ~0.1Ω shunt). Clamp meter: 0–1000A AC non-contact.
Where the Ammeter symbol is used
- Panel meters on generator and alternator outputs monitoring supply current in industrial and marine systems
- Motor control panel boards measuring running current to detect overload or phase loss conditions
- Battery charge/discharge monitoring in solar, EV, and UPS systems showing charge and load current
- Laboratory bench circuits during component testing and circuit debugging
- Power quality analysers monitoring branch circuit current for load balancing and billing
- Automotive electrical diagnostics measuring starter motor current and alternator output
- Educational electronics circuits demonstrating Ohm's law and Kirchhoff's current law
Example
In a three-phase motor control circuit, an Ammeter symbol is shown on the R-phase supply line between the main contactor and the motor terminals, connected via a current transformer (5A secondary) to keep panel meter wiring safe; the ammeter reads the motor running current to allow the operator to monitor for overload conditions before the thermal protection relay trips — the Ammeter symbol on the schematic immediately identifies the current monitoring point and the CT-indirect measurement method.
Key facts
- The Ammeter symbol is a circle containing the letter 'A', with two series terminals (In and Out), inserted along a conductor path to measure current in amperes (A, SI base unit, IEC 80000-6).
- An ammeter is always connected in series with the circuit being measured; connecting it in parallel causes a near-short-circuit due to the instrument's very low internal resistance.
- The ideal ammeter has zero internal resistance; practical ammeters have milliohm-level resistance to minimise voltage burden (voltage drop across the measurement point).
- For high currents (above 5A), ammeters are connected indirectly through a current transformer (CT) rated with a standard 5A secondary, keeping the panel meter isolated from high voltages.
- The Ammeter symbol is defined in IEC 60617-08 and ANSI Y32.2 / IEEE 315-1975 as a circle with 'A' inside; both standards use the identical glyph.
- Accuracy classes for panel-mounted ammeters are defined in IEC 60051: Class 0.5 means maximum error ±0.5% of full-scale reading.
- The unit of electric current is the ampere (A), one of the seven SI base units, defined since 2019 as the flow of 1/1.602176634×10⁻¹⁹ elementary charges per second.
Diagrams that use this symbol
- strain gauge diagram
- amp diagram
- rpm gauge wiring diagram
- tach wiring diagram
- tachometer wiring diagram
- ammeter circuit diagram
- fuel gauge wiring diagram
- wire gauge diagram
Frequently asked questions
What does the ammeter symbol mean in a circuit diagram?
The ammeter symbol means an electric current measurement device is inserted in series at that point. The circle with 'A' indicates that the instrument measures and displays the magnitude of current (in amperes) flowing through the series circuit path between the In and Out terminals.
What does the ammeter symbol look like?
The ammeter symbol is a circle with the capital letter 'A' inside. Two conductor lines connect to opposite sides of the circle (In and Out), showing the series current path through the instrument. In power system diagrams a CT (current transformer) symbol is often shown upstream of the ammeter to indicate indirect measurement.
Why is an ammeter connected in series and not in parallel?
An ammeter has very low internal resistance (milliohms) and must be connected in series so that all of the circuit current flows through it, producing a measurable voltage drop proportional to the current. Connecting an ammeter in parallel across a circuit would cause a near-short-circuit, damaging the instrument and disrupting the circuit due to the ammeter's negligible resistance.
What is the difference between an ammeter symbol and a voltmeter symbol?
The ammeter symbol is a circle with 'A' inside, connected in series in the circuit. The voltmeter symbol is a circle with 'V' inside, connected in parallel (across two nodes) to measure voltage difference. An ammeter measures current; a voltmeter measures voltage. The series vs. parallel connection is the critical operational difference.
How many terminals does the ammeter symbol have?
The ammeter symbol has two terminals: In (current entry) and Out (current exit). These are the two series connection points in the circuit. Physical ammeters may have a +/− polarity on DC instruments; for AC measurement there is no polarity distinction. High-range panel ammeters also have a separate CT secondary terminal pair in addition to the panel terminal screws.
What standard defines the ammeter symbol?
The ammeter symbol is defined in IEC 60617-08 (measuring instruments and signal sources) and ANSI Y32.2 / IEEE 315-1975. Both standards specify a circle with the letter 'A' inside and two series terminals. The two standards use identical graphical representations for this symbol.
What unit does the ammeter measure?
The ammeter measures electric current in amperes (A), the SI base unit for current defined in IEC 80000-6. Common submultiples used in electronics are the milliampere (mA = 10⁻³ A) and microampere (µA = 10⁻⁶ A). Large industrial and utility currents are measured in kiloamperes (kA = 10³ A).
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