In physics equations, the magnetic force symbol is FB (or Fm with a vector arrow for directional notation). However, on the workbench and in electrical schematics, we rarely calculate raw Lorentz forces. Instead, we interact with components that generate or react to magnetic force—electromagnets, solenoids, relays, and contactors. Below is the master reference table bridging the gap between theoretical physics notation and the standardized IEC/ANSI schematic symbols you will actually encounter in control panels and circuit diagrams.

Master Reference: Magnetic Force & Actuator Symbols

Concept / Component Physics Notation IEC 60617 Schematic Symbol ANSI/IEEE 315 Designation Typical Bench/Jobsite Application
Magnetic Force (Lorentz) FB or Fm N/A (Mathematical Variable) N/A Calculating motor torque or Hall effect sensor deflection
Magnetomotive Force (MMF) ℱ or Fm N/A N/A Sizing transformer cores and magnetic amplifiers
Solenoid / Electromagnet Coil N/A Rectangle with a solid diagonal line Circle or Rectangle (Prefix 'L' or 'K') Pneumatic valve actuators, contactor pull-in coils
Magnetic Flux Density B N/A N/A Calibrating reed switches and proximity sensors
Inductor (Passive, no moving armature) L Series of semicircular loops Series of semicircular loops Filtering, buck/boost converters (Do not confuse with solenoids)

Decoding the Symbols: Physics vs. Schematic Practice

The biggest point of confusion for DIYers and junior technicians is conflating the physics variable for magnetic force with the schematic symbol for a magnetic actuator. When you are reading a textbook or a NIST standards document, FB represents the physical push or pull exerted on a moving charge or current-carrying wire in a magnetic field. You use this when calculating the torque of a DC motor or the deflection of an electron beam. But when you are troubleshooting a 24VDC pneumatic control panel, you are looking for the solenoid symbol. Under the globally dominant IEEE 315 / IEC 60617 standards, a solenoid (a coil designed to convert electrical energy into linear mechanical magnetic force) is drawn as a rectangle with a solid diagonal line cutting across it. That diagonal line is the critical differentiator—it tells you this coil has a moving iron core (an armature) that will physically shift when energized, unlike a standard inductor which is drawn as a series of loops and simply stores energy in a magnetic field.
Bench Tip: If you see a rectangle with a diagonal line on a schematic, expect to measure a specific DC resistance. A typical 24VDC industrial solenoid valve coil will read between 15Ω and 40Ω on your multimeter. If it reads OL (open), the internal fine-gauge wire has burned out from overheating.

Regional Variants: IEC vs. ANSI vs. NEMA

While the physics symbols (FB, B, ℱ) are universal across all global scientific literature, the schematic symbols for the components that produce magnetic force vary depending on the age and region of the blueprint.
Standard Region / Era Solenoid / Electromagnet Symbol Style Where You Will See It
IEC 60617 Global / EU / Modern US Rectangular box with a diagonal line. Terminals labeled A1/A2. Modern PLC schematics, international machinery, new US control panels.
ANSI/IEEE 315 US / Legacy Often a circle with 'SOL' inside, or a rectangle with loops. Terminals labeled with numbers. Older US industrial equipment, military surplus, vintage HVAC diagrams.
NEMA US Industrial (Heavy) Similar to ANSI but heavily relies on alphanumeric prefixes (e.g., 'M' for motor starter magnetic coil). Heavy motor control centers (MCCs), high-voltage switching gear.
If you are working on imported European machinery (like a German CNC mill), you will strictly see the IC 60617 rectangular boxes. If you are troubleshooting a 1980s American lathe, expect ANSI circles and NEMA prefixes.

Rows People Get Wrong & Faded Marking Protocols

Even experienced makers make specific mistakes when interpreting magnetic force symbols and identifying physical components on the bench. Here are the most common errors and how to safely resolve them.

1. Confusing MMF (ℱ) with Magnetic Flux (Φ)

In magnetic circuit design (like sizing a custom transformer core), people mix up Magnetomotive Force (ℱ, measured in Ampere-turns) with Magnetic Flux (Φ, measured in Webers). Think of ℱ as the electrical 'pressure' pushing the magnetic field, analogous to voltage. Think of Φ as the actual volume of magnetic field lines flowing through the core, analogous to current. Getting these swapped in your calculations will result in a core that saturates instantly and overheats.

2. The Inductor vs. Solenoid Trap

As noted in the master table, an inductor (loops) and a solenoid (rectangle with diagonal) look vaguely similar to a rushed reader. Wiring a flyback diode across an inductor is standard practice to manage voltage spikes. However, if you misread the symbol and treat a heavy-duty AC contactor coil (which generates massive magnetic force to pull in mechanical contacts) as a simple DC inductor, you will destroy your driving transistor. AC magnetic coils require RC snubber networks, not simple diodes, to manage the collapsing magnetic field.

Safe Interpretation of Faded Physical Markings

Warning: Never apply arbitrary mains voltage to an unmarked magnetic coil. A 24VAC coil subjected to 120VAC will draw massive current, overheat, and potentially catch fire within seconds.
When you are replacing a burned-out solenoid or contactor coil and the physical nameplate is faded, melted, or missing, do not guess the voltage based on the schematic symbol alone. Use this safe verification protocol:
  1. Measure the Coil Resistance: Use your multimeter. A 12VDC coil typically reads 2Ω to 10Ω. A 24VDC coil reads 15Ω to 50Ω. A 120VAC coil will read significantly higher (often 400Ω to 2,000Ω depending on the VA rating).
  2. Check the Flyback Protection: Look at the driving circuit. If there is a diode physically soldered across the coil terminals or on the driver board, it is almost certainly a DC coil. If there is a small capacitor and resistor in series (an RC snubber), it is an AC coil.
  3. Low-Voltage Ramp Test: If you must energize it to test mechanical movement, use a bench power supply. Start at 5VDC and slowly ramp up while monitoring the current draw. A healthy coil will pull in its armature smoothly at its rated voltage without the current spiking uncontrollably.
By understanding both the theoretical FB variable and the practical IEC/ANSI schematic symbols, you can seamlessly transition from calculating magnetic forces on a whiteboard to troubleshooting the physical solenoids that move your machinery.