When reading a schematic or designing a printed circuit board (PCB), guessing at component icons leads to reversed polarities, shorted gates, and failed board spins. The two global authorities for schematic graphics are IEC 60617 (the international standard) and IEEE 315 / ANSI Y32.2 (the US standard). This reference merges standard component symbols with the physical wire designations and ampacity derating rows you need to transition from a digital schematic to a physical, code-compliant build.

How to Read This Electronic Symbols & Derating Chart

This reference is split into two functional domains: schematic logic and physical power. The first table maps visual icons to their standardized reference codes. The columns are structured as follows: Symbol Description, IEC 60617 Reference, IEEE 315 Reference, and Primary Function.

The second table bridges schematic wire designators to physical installation limits. It uses the temperature rating columns defined in NEC Table 310.16: 60°C (140°F), 75°C (167°F), and 90°C (194°F). The final column provides the Derating Multiplier for bundling. Always read the wire table from left to right, stopping at the lowest temperature rating present in your circuit's termination chain.

Bench Tip: If your schematic software (like KiCad or Altium) defaults to IEEE symbols but your manufacturing house is in Europe, switch your library to IEC 60617 to prevent misinterpretation of switch states and relay coils during assembly.

Core Component Symbols (IEC 60617 & IEEE 315)

Below is the master lookup for the most frequently queried schematic icons. We have included anchor tags for the most common bookmark targets: MOSFETs, Grounding, and Polarized Capacitors.

Component IEC 60617 Ref IEEE 315 Ref Function & Visual Identifier
Resistor S00121 12-2-1 Current limiting. IEC uses a rectangle; IEEE uses a zigzag line.
Capacitor (Polarized) S00126 12-7-2 Energy storage. One straight plate, one curved plate. Curve indicates the negative/outer foil terminal.
Inductor S00135 12-4-1 Magnetic storage. Depicted as a series of half-circles (coils) over a line.
Zener Diode S00341 12-21-2 Voltage regulation. Standard diode triangle with a cathode bar bent into a 'Z' shape.
NPN BJT S00201 12-14-1 Current amplification. Circle with an arrow pointing OUT from the emitter.
N-Channel MOSFET (Enhancement) S00234 12-15-2 Voltage-controlled switching. Gate is isolated from the channel line; arrow on source points IN. Dashed channel line indicates normally-off (enhancement mode).
Operational Amplifier S00583 12-33-1 Signal conditioning. Triangle pointing right. '+' is non-inverting, '-' is inverting input.
Chassis / Signal Ground S00266 12-24-2 Reference potential. Three horizontal lines of decreasing width. IEC often uses a simple downward arrow or rake for earth ground.
SPST Switch (Normally Open) S00186 12-11-1 Circuit control. A gap in the line with a hinged lever resting above the contact point.
Transformer (Iron Core) S00411 12-6-2 Voltage isolation/stepping. Two inductor coils separated by two parallel vertical lines indicating the laminated core.

Source references: IEC Graphical Symbols Database and IEEE Std 315-1975.

Wire Symbols, Ampacity, and How Derating Rows Modify Base Values

Schematics often label power nets with wire gauges (e.g., NET_12AWG_THHN). Translating that schematic label into physical wire requires understanding ampacity limits and bundling penalties. The table below outlines the base ampacities for copper conductors and the mandatory derating multipliers.

AWG Size 60°C Column (NM-B / TW) 75°C Column (THWN / Terminals) 90°C Column (THHN / XHHW) Derating Row (4-6 Conductors in Raceway)
14 AWG 15A 20A 25A x 0.80 (80%)
12 AWG 20A 25A 30A x 0.80 (80%)
10 AWG 30A 35A 40A x 0.80 (80%)
8 AWG 40A 50A 55A x 0.80 (80%)
6 AWG 55A 65A 75A x 0.80 (80%)

Which Column Applies to Your Installation?

The rule of thumb is the weakest link principle. Even if you pull 90°C THHN wire through your conduit, the circuit breakers, lugs, and terminal blocks you terminate into are almost universally rated for 75°C (or 60°C for older residential panels). Therefore, your final allowable ampacity is capped by the 75°C column. You only use the 90°C column as a starting point before applying derating factors.

How Derating Rows Modify the Base Value

When you bundle multiple current-carrying conductors in a single conduit or cable tray, they trap heat. The "4-6 Conductors" derating row dictates that you must multiply the wire's base 90°C ampacity by 0.80 (80%).

Worked Example: You are pulling four 12 AWG THHN current-carrying wires in a single EMT conduit for a 24V DC motor array.

  • Base 90°C ampacity for 12 AWG = 30A.
  • Apply derating row: 30A × 0.80 = 24A maximum allowable current.
  • Check termination limit: Your motor controller terminals are rated 75°C (25A limit). Since 24A < 25A, the 12 AWG wire is acceptable. If you needed 25A exactly, you would have to step up to 10 AWG.
What This Table Cannot Tell You: This chart assumes an ambient temperature of 30°C (86°F). If your conduit runs across a hot roof or near a boiler, you must apply an additional ambient temperature correction factor from NEC Table 310.15(B)(1). Furthermore, this table does not account for voltage drop. A 14 AWG wire might be thermally safe at 12A, but if the run is 150 feet, the voltage drop will starve your load. Always calculate voltage drop for runs over 100 feet.

Electronic Symbols Chart FAQ

What is the difference between IEC and IEEE electronic symbols?

The primary difference is geographical and stylistic. IEC 60617 is the international standard (dominant in Europe, Asia, and modern global CAD tools) and favors abstract, rectangular shapes—like a simple box for a resistor. IEEE 315 (often overlapping with ANSI Y32.2) is the US standard and favors pictorial representations—like the traditional zigzag line for a resistor. Modern EDA tools like Altium and KiCad allow you to toggle between these symbol libraries, but you should never mix them on a single schematic sheet, as it creates ambiguity in switch states and relay logic.

How do I read the polarity marks on a polarized capacitor symbol?

On a polarized capacitor symbol (typically an electrolytic or tantalum), one plate is drawn as a straight line and the other as a curved line. The curved line always represents the negative terminal (the cathode). Additionally, the positive terminal (anode) is usually marked with a "+" sign. If you are looking at a schematic where the capacitor symbol is just two parallel lines but one has a "+" next to it, it is still polarized; the "+" dictates the anode. Reversing a tantalum capacitor in physical builds will result in catastrophic thermal failure and venting.

Why does my schematic use a different ground symbol than this chart?

Ground is not a single concept; it is a hierarchy. While the chart above shows the standard chassis/signal ground (three decreasing horizontal lines), you will frequently encounter two other variants. Earth Ground (a line with three downward-pointing diagonal spikes) indicates a physical connection to the earth via a grounding rod, used for safety and mains fault clearing. Analog/Digital Ground (a hollow triangle pointing down) is used in mixed-signal PCB design to separate noisy digital return currents from sensitive analog return currents, tying them together at a single star point to prevent ground loops.

Does this electronic symbols chart cover European wiring color codes?

No. Schematic symbols dictate logical function on a page, while wire color codes dictate physical installation safety. If you are building a physical harness based on an IEC schematic, you must follow IEC 60446 for wire colors. Under IEC 60446, the protective earth (PE) is strictly Green/Yellow stripe, the neutral (N) is Blue, and the line/phases (L1, L2, L3) are Brown, Black, and Grey. This differs significantly from US NEC practice, where neutral is White or Grey, and ground is Green, Bare, or Green/Yellow. Always verify the regional standard of the physical installation site, not just the schematic origin.