Megohms

A megohm is a unit of electrical resistance equal to one million ohms (1 MΩ = 10^6 Ω). It is used to express very large resistances in electronics and electrical engineering, such as insulation resistance and high-value resistors.

The symbol for megohm is MΩ. In specifications and schematics, resistance values are commonly written with SI prefixes, for example 4.7 MΩ. The prefix mega- comes from the Greek megas, meaning large, and the symbol is uppercase M in this context.

Megohms are commonly encountered in applications involving insulation and leakage. They are used to describe the resistance of insulation materials, cables, motors, and other high-impedance components. They also appear in high-impedance circuits and in sensor inputs where very low currents are expected.

Measurement of megohms is performed with instruments capable of high-resistance ranges, such as insulation testers or digital multimeters configured for high-range, sometimes using a dedicated megohm scale. These devices apply a test voltage and measure the resulting current to calculate resistance.

Interpretation of megohm readings depends on context. Higher megohm values generally indicate better insulation and lower leakage, while lower values suggest higher leakage or degraded insulation. Temperature and moisture can influence high-resistance measurements, so readings are often specified under controlled conditions.