The symbol for AC volts on a digital multimeter is V~ (a capital V with a tilde or wavy line above it). On electrical schematics, an AC voltage source is represented by a sine wave inside a circle, while text labels on power supplies and PCBs typically use VAC or Vrms. If you are looking at a legacy diagram, you might also see a lowercase Vac.
Knowing exactly which symbol you are looking at is the difference between a successful troubleshooting session and a blown multimeter fuse—or worse, an arc flash incident. Below is the definitive reference for identifying AC voltage markings across different tools, standards, and regions.
The Complete AC Voltage Symbol Reference Table
Use this spec-sheet-table to quickly identify the marking you are looking at, whether you are holding a handheld meter, reading a control panel silk-screen, or reviewing an AutoCAD schematic.
| Context / Location | Symbol or Marking | Governing Standard | Practical Meaning & Bench Application |
|---|---|---|---|
| Multimeter Dial / Display | V~ (V with tilde) | IEC 60417-5216 | Selects the AC voltage measurement function. The tilde represents the sinusoidal waveform of alternating current. |
| Schematic Diagram (Source) | ~ inside a circle | IEEE 315 / IEC 60617 | Denotes an ideal AC voltage source (like a generator or secondary winding of a transformer). |
| PCB Silk-screen / Power Labels | VAC or Vrms | Industry Convention | Indicates the nominal alternating voltage. Vrms specifies that the value is the Root Mean Square (effective heating value), not peak voltage. |
| Legacy / Obsolete Prints | Vac (lowercase ac) | Older US/UK drafts | Same as VAC, but commonly found on schematics drawn before the 1990s standardization push. |
| Oscilloscope Display | Vpp or Vp-p | IEEE 1057 | Peak-to-peak AC voltage. Crucial distinction: a 120V Vrms wall outlet will show ~340Vpp on a scope. |
Regional Standards and Faded Markings
While the V~ symbol is nearly universal on modern test equipment, the underlying standards that dictate how these symbols are drawn on schematics and panels vary by region.
Which Standard Applies to Your Region?
- International (IEC 60417 & IEC 60617): Used across Europe, Asia, and most of the world. The sine wave and tilde are strictly defined. If you are reading a schematic from a European manufacturer (like Siemens or ABB), expect strict adherence to IEC graphical symbols.
- North America (ANSI/IEEE 315): The US and Canada largely follow IEEE 315 for schematic symbols. While the sine wave in a circle is standard for AC sources, you will frequently see text-based designations (VAC) preferred over graphical symbols on industrial control panel silk-screens to comply with UL508A readability requirements.
- Older UK (BS 3939): Before harmonizing with IEC standards, British Standard 3939 used slightly different proportions for the sine wave and occasionally relied on text annotations like 'a.c.' next to a standard battery symbol to denote alternators. You will only encounter this on legacy marine or industrial prints from the 1970s and 80s.
Safe Interpretation When Markings are Faded or Missing
On a 20-year-old bench meter or a sun-baked outdoor disconnect, the printed tilde (~) over the 'V' is often the first thing to rub off. If you are holding a meter and cannot clearly distinguish the AC setting from the DC setting (V⎓), use these contextual clues:
- Look for the 'Hz' marker: The AC voltage setting is almost always grouped with, or doubles as, the frequency (Hz) measurement function. If a dial position has a small 'Hz' printed next to it, that is your AC volts setting.
- Check the range limits: Basic multimeters usually have a dedicated 200mV or 2V range for DC. AC voltage dials rarely go below 2V or 6V because measuring millivolt AC signals requires specialized True-RMS circuitry. If the range starts at 6V or 60V, it is likely the AC setting.
- The Probe Jack Test: If the dial is completely illegible, do not guess on a live circuit. Use a known 1.5V AA battery. If the meter reads '-1.5' or '1.5', you are on DC. If it reads '0.00' or fluctuates wildly, you are on AC.
Symbols and Rows People Get Wrong
Even experienced technicians make assumptions about AC voltage symbols that lead to measurement errors or blown equipment. Here are the most common pitfalls on the bench.
1. Confusing V~ (Volts) with A~ (Amps)
The tilde simply means 'Alternating'. If you accidentally set your dial to A~ instead of V~ and probe across a 120V receptacle, you are creating a dead short through the meter's internal shunt. This will instantly blow the meter's high-amp fuse (usually a 10A or 20A HRC ceramic fuse) and can cause an arc flash if the meter lacks proper CAT III/IV safety certification. Always verify the 'V' is present, not an 'A' or 'mA'.
2. Assuming V~ Means True-RMS
The V~ symbol only tells you the meter is measuring AC voltage; it does not tell you how it calculates it. A cheap average-responding meter will display the V~ symbol, but it assumes the waveform is a perfect sine wave. If you use it to measure the output of a variable frequency drive (VFD), a UPS, or a dimmer circuit, the reading will be wildly inaccurate. For non-linear loads, you must look for the True-RMS badge on the meter (like the Fluke 87V or 117) alongside the V~ symbol.
3. Vrms vs. Vp-p on Schematics
When reading AC waveform theory and schematics, confusing RMS with Peak-to-Peak is a classic error. If a schematic specifies a transformer secondary output of '24 VAC', it means 24 Vrms. The peak voltage hitting your rectifier diodes will actually be about 34V (24 × √2). If you size your filter capacitors based on 24V, they will overvolt and fail. Always assume schematic AC values are RMS unless explicitly marked as Vp or Vpp.
Frequently Asked Questions
What does the wavy line mean on a multimeter?
The wavy line (tilde, ~) is the universal graphical representation of a sine wave, which is the standard waveform for alternating current (AC) power. When placed over a 'V', it tells the meter's internal microcontroller to switch the analog-to-digital converter (ADC) into AC-coupled mode, blocking any DC offset and calculating the RMS value of the alternating signal.
Is VAC the same as Vrms?
In practical, everyday electrical work, yes. When a utility company says your home is supplied with '120 VAC', they mean 120 Vrms (Root Mean Square). Vrms is the effective voltage that delivers the same heating power to a resistive load as a DC voltage of the same value. However, in strict electronics engineering, 'VAC' just denotes the presence of alternating voltage, while 'Vrms' specifies the exact mathematical method used to quantify it.
How do I measure AC volts if the symbol is rubbed off my meter?
If the dial text is completely gone, look for the 'Hz' symbol, as AC voltage and frequency share the same dial position on 90% of multimeters. Alternatively, look for the highest voltage range on the dial (usually 600V or 750V). On basic meters, the 600V/750V position is almost exclusively reserved for AC mains measurements, whereas DC measurements usually top out at a dedicated 1000V position or include a 200mV range nearby. When in doubt, test against a known 9V battery; if the meter reads zero or fluctuates, you are on the AC setting.
What is the schematic symbol for an AC voltage source?
On modern electrical schematics, an AC voltage source is drawn as a circle with a continuous sine wave inside it. This is defined by both IEC 60617 and IEEE 315 standards. In older or more simplified wiring diagrams, you may instead see a circle with a tilde (~) inside, or simply a standard DC battery symbol (two parallel lines of unequal length) with the text 'AC' or 'Alternator' written next to it to save drafting time.
