megahenry

A megahenry (MH) is one million henries, the SI unit used to quantify electrical inductance. Inductance measures how strongly a conductor or coil opposes changes in electric current by generating a magnetic field. The megahenry sits at the upper end of practical inductance measurement, used for large industrial coils, power transmission components, and electromagnetic equipment rather than small circuit components measured in millihenries or microhenries.

Inductance depends on three physical factors: the number of wire turns in a coil, the cross-sectional area enclosed by those turns, and the magnetic permeability of the core material. A coil with many turns, a large area, or a ferromagnetic core like iron will have higher inductance. To reach megahenry values, you need either very many turns, very large coils, or both. A single-turn loop of wire a few centimetres across might measure in nanohenries; a massive multi-turn coil with a ferromagnetic core can easily reach megahenries.

Where megahenries appear

Power distribution systems use megahenry-scale inductances in transformers, reactors, and AC inductors that smooth current flow or limit fault currents. Large synchronous motors and generators have stator and rotor inductances in this range. Precision measuring equipment, such as inductance bridges used to characterize unknown coils, must operate over decade ranges that include megahenries. Coil designers working on high-power applications calculate inductance values in megahenries to predict magnetic energy storage and current response times.

Measuring megahenry inductances requires care because stray resistance, capacitance, and core losses become significant sources of error at this scale. Direct current resistance must be accounted for separately from inductance. At power frequencies like 50 or 60 Hz, ferromagnetic cores show nonlinear behaviour and hysteresis loss that complicates measurement. Bridge circuits, Q-meters, and LCR meters designed for high inductance ranges are the standard tools.

The term henries itself honours physicist Joseph Henry, whose work on electromagnetism in the 1830s laid groundwork for electromagnetic induction. The SI prefix mega denotes multiplication by 10⁶, following the systematic naming convention that runs from pico through mega and beyond. Understanding inductance in megahenries is essential for anyone designing or troubleshooting large inductive circuits, power supplies, or electromagnetic devices.