The standard voltmeter schematic symbol is a circle containing a capital "V" under North American ANSI/IEEE 315 standards, or a circle/rectangle with a "V" and specific waveform modifiers under international IEC 60617 standards. Because metering symbols vary by region, era, and drafting software, misreading them can lead to catastrophic wiring errors—such as placing a low-impedance ammeter in parallel with a 480V bus. Below is the complete reference table for metering symbols to ensure accurate schematic interpretation.
Complete Voltmeter & Metering Symbol Reference Table
This table covers the primary metering symbols you will encounter on electrical single-line diagrams, motor control center (MCC) schematics, and PCB layouts. Always verify the standard (ANSI vs. IEC) listed in the title block of your drawing before assuming a symbol's meaning.
| Meter Type | ANSI/IEEE 315 Symbol | IEC 60617 Symbol | Connection Topology | Practical Meaning & Internal Impedance |
|---|---|---|---|---|
| DC Voltmeter | Circle with "V" and solid/dashed underline | Circle/Rectangle with "V" and solid line | Parallel | Measures potential difference in DC circuits. High internal impedance (typically >10 MΩ) to prevent loading the circuit. |
| AC Voltmeter | Circle with "V" and tilde (~) or sine wave | Circle/Rectangle with "V" and tilde (~) | Parallel | Measures RMS AC voltage. Often connected via Potential Transformers (PTs) in medium/high voltage systems. |
| Ammeter (AC/DC) | Circle with "A" (tilde/line for AC/DC) | Circle/Rectangle with "A" | Series (or via CTs) | Measures current flow. Extremely low internal impedance. Never wire in parallel. |
| Ohmmeter | Circle with "Ω" (Omega) | Circle/Rectangle with "Ω" | Isolated Component | Measures resistance. Contains an internal current source; must only be used on de-energized circuits. |
| Wattmeter | Circle with "W" and four terminals | Circle/Rectangle with "W" and four terminals | Series & Parallel | Measures real power (Watts). Has separate current (series) and voltage (parallel) coils. |
| Galvanometer | Circle with "G" | Circle/Rectangle with "G" | Series | Detects minute currents or null conditions (e.g., in a Wheatstone bridge). Highly sensitive, low current capacity. |
Regional Standards: ANSI/IEEE vs. IEC Variants
The visual representation of the voltmeter schematic symbol depends heavily on the geographic origin of the engineering firm and the CAD library used. Understanding these regional differences is critical when working on international projects or maintaining legacy equipment.
North America: ANSI/IEEE 315
In the US and Canada, schematic symbols are governed by IEEE 315 (formerly ANSI Y32.2). The standard strictly favors the circle as the base shape for all indicating meters. The letter inside the circle dictates the function (V, A, W), while a small modifier above or below the letter indicates the current type (a straight line for DC, a tilde for AC). If a meter is a "recording" type (like a chart recorder), a small arrow pointing to a stylized paper roll is added to the bottom right of the circle.
International & Europe: IEC 60617
The International Electrotechnical Commission (IEC) standard 60617 allows for more geometric flexibility. While the circle is still widely used, IEC schematics frequently use a square or rectangle to denote solid-state or digital panel meters, reserving the circle for traditional analog moving-coil or moving-iron meters. Furthermore, IEC diagrams often place the unit of measurement (e.g., "kV" or "mV") directly inside the symbol rather than just the base letter "V".
Legacy UK: BS 3939
If you are troubleshooting older British infrastructure, you may encounter BS 3939 symbols. This standard was largely harmonized with IEC in the late 20th century, but legacy prints often feature a circle with a "V" and a specific internal hash-mark pattern to denote the meter's class of accuracy or its specific movement type (e.g., dynamometer vs. induction). Always cross-reference the drawing's date; if it predates 1990, assume BS 3939 conventions may apply.
Rows People Get Wrong: Common Schematic Misinterpretations
Even experienced electricians and bench technicians misread specific meter symbols when skimming complex single-line diagrams. Here are the most common pitfalls and how to avoid them.
A wattmeter symbol (W) looks similar to a voltmeter (V), but a wattmeter has four connection terminals (two for the current coil, two for the voltage coil). If you wire a wattmeter's voltage terminals in series with a load, or fail to wire the current coil in series, you will either blow the internal fuse or create a dead short. Always count the connection nodes on the symbol.
- Confusing the AC Voltmeter with an AC Source: An AC voltmeter is a circle with a "V" and a tilde (~). An AC voltage source (like a generator or the grid) is often just a circle with a tilde inside, or a circle with a sine wave, but no letter. If there is no "V", it is a source, not a meter.
- The "V" vs. "U" in Faded Prints: In motor control schematics, a "U" often denotes an Under-Voltage relay coil, not a voltmeter. A voltmeter (V) will have two wires connected in parallel across the phases. An under-voltage relay (U) will be part of a control logic string and will have a contact output associated with it elsewhere on the page.
- Digital vs. Analog Assumptions: Under IEC standards, a square meter symbol implies a digital readout (which may have high-frequency sampling and different burden characteristics), while a circle implies an analog dial. Assuming an analog meter's damping characteristics apply to a digital meter can lead to incorrect transient readings.
Safe Interpretation When Markings Are Faded or Missing
In industrial environments, UV exposure, heat, and chemical off-gassing can fade schematic prints inside control panels. If the letter inside the meter symbol is illegible, you must determine whether the device is a voltmeter or an ammeter before proceeding with any troubleshooting. Standard schematic conventions dictate that the wiring topology will always reveal the meter's true identity.
- De-energize and Verify: Before opening any panel, turn off the main disconnect, apply Lockout/Tagout (LOTO), and verify the absence of voltage using a known-working CAT III or CAT IV multimeter.
- Trace the Wiring Topology:
- Voltmeters are wired in parallel. The wires will tap directly off the busbars, phase-to-phase, or phase-to-neutral. They will almost always be protected by small inline fuses (e.g., 1A to 5A midget fuses) to protect the meter's internal high-impedance coil.
- Ammeters are wired in series. In systems above 50A, they are not wired directly into the power path; instead, they connect to the secondary side of Current Transformers (CTs).
- Look for the Shorting Block: This is the definitive test. Ammeters connected to CTs must have a make-before-break shorting terminal block installed between the CT and the meter. This allows technicians to safely short the CT secondary before removing the meter. Voltmeters do not use shorting blocks. If you see a shorting block, the faded symbol is an ammeter.
Frequently Asked Questions
What does the voltmeter schematic symbol look like in PLC ladder logic?
In PLC programming environments (like Rockwell Studio 5000 or Siemens TIA Portal), the traditional electrical voltmeter symbol is rarely used in the logic itself. Instead, voltage measurement is represented by an Analog Input (I:Tag) instruction or a scaling block (e.g., a CPT or SCL instruction) that converts a 4-20mA or 0-10V signal from a voltage transducer into an engineering unit. However, on the electrical wiring diagrams accompanying the PLC cabinet, the standard ANSI/IEEE circle-with-V symbol is used to denote the physical panel-mounted display or the transducer feeding the PLC's analog input card.
How do I differentiate an AC voltmeter symbol from a DC voltmeter symbol?
Look at the modifier adjacent to the "V". For an AC voltmeter, there will be a tilde (~) or a small sine wave drawn either above the "V" or to its right. For a DC voltmeter, there will be a solid straight line, often with a dashed line beneath it (representing the steady DC waveform with minor ripple). If neither is present, the drawing's title block or the specific circuit context (e.g., a battery bank vs. a transformer secondary) will dictate the current type. When in doubt, assume AC and use appropriately rated CAT III/IV test equipment.
Why does my schematic show a voltmeter symbol with two overlapping circles?
Two overlapping circles with a "V" typically denote a dual-element or polyphase voltmeter, or a meter with a transferred scale (e.g., a single physical meter on the panel that can be switched to read Phase A-B, B-C, or C-A via a rotary voltage selector switch). The overlapping circles represent the multiple measurement paths or the selector switch mechanism integrated into the metering circuit. Always check the adjacent selector switch symbol to understand how the meter is being fed.
