hectoampere

A hectoampere (hA) is 100 amperes, a unit of electrical current sitting one level above the ampere in the SI prefix hierarchy. The symbol is hA. Despite being a legitimate SI unit, it sees almost no use in industrial measurement or equipment specification.

The ampere itself is the base SI unit of electrical current, defined by the force between parallel conductors carrying current. The hectoampere prefix (hecto-, meaning 100) follows the standard metric pattern: kilo (1000), hecto (100), deca (10), then the base unit. In theory, any quantity measured in amperes can be expressed in hectoamperes by division by 100.

Practically, the hectoampere occupies an awkward middle ground. Equipment operating at tens of amperes uses that unit directly. Heavy industrial systems handling hundreds of amperes often jump to kiloamperes (kA), which compress the numbers further. A 500 A power supply reads as 500 A or sometimes 0.5 kA, never 5 hA. Current ranges from laboratory instruments (milliamps), to welding equipment (100s of amps), to smelters and power transmission (kiloamperes and beyond) all skip over the hectoampere as unnecessary.

The hectoampere does appear in SI-compliant specifications and textbooks, where completeness matters more than practicality. Metrologists and standards bodies recognize it because it follows the SI system logically. But working technicians and engineers almost never encounter it in datasheets, equipment nameplates, or test reports. When 100 A needs to be stated, it is stated plainly as 100 A.