What current density is safe for copper wire?

Safe current density depends on insulation type and cooling. General guidelines: 3-6 A/mm² for enclosed wiring, up to 10 A/mm² for well-cooled conductors. Magnet wire in motors: 4-8 A/mm². Higher density requires better cooling to prevent insulation damage.

How does skin effect change current density?

At high frequencies, current concentrates near conductor surface (skin effect). The skin depth δ = √(2ρ/ωμ) defines penetration. At 60 Hz in copper, δ ≈ 8.5 mm; at 1 MHz, δ ≈ 0.066 mm. This increases effective resistance and localized current density at the surface.

Why does higher current density cause more heating?

Power dissipation per volume = J²ρ (current density squared times resistivity). Doubling current density quadruples the heat generated per unit volume. This is why conductor sizing is critical—larger cross-section means lower J for the same total current, dramatically reducing heating.

How do I calculate current density in a wire?

J = I/A where I is current and A is cross-sectional area. For round wire: A = πd²/4. Example: 15 A through AWG 14 wire (diameter 1.63 mm): A = 2.08 mm², so J = 15/2.08 = 7.2 A/mm². This is within typical limits for building wire with good ventilation.

面電流密度 Converter

About Surface Current Density Conversion

Surface current density (more precisely, current density through a cross-section) measures current flow per unit cross-sectional area—amperes per square meter. It describes how concentrated current is within a conductor, critical for evaluating heating, material limits, and electromagnetic effects in conductors. High current density means more electrons crowding through less area, creating more collisions with the lattice and thus more resistive heating.

The SI単位 is amperes per square meter (A/m²), though the practical unit A/mm² dominates engineering work. Current density determines resistive heating through P = J²ρV (power equals density squared times resistivity times volume), making it the key parameter for thermal design. Current density also determines magnetic field strength inside and around conductors, affecting inductance and proximity effects in cables and windings.

Our converter handles current density units used in electrical engineering, wire sizing, and power system design.

Common Surface Current Density Conversions

変換元	変換先	乗数
A/m²	A/mm²	10⁻⁶
A/mm²	A/m²	10⁶
A/m²	A/cm²	10⁻⁴
A/cm²	A/m²	10⁴
A/m²	mA/mm²	10⁻³
A/m²	kA/m²	0.001
kA/m²	A/m²	1,000
mA/cm²	A/m²	10
A/m²	mA/cm²	0.1

Surface Current Density 単位リファレンス

Ampere per square meter (A/m²) – The SI単位 for current density, expressing current per unit cross-sectional area. In practice, A/m² yields very large numbers: 1 A/mm² = 1,000,000 A/m². Primarily used in physics equations and electromagnetic field calculations where SI consistency matters. Maxwell's equations and textbooks use A/m² for dimensional analysis.

Ampere per square millimeter (A/mm²) – The dominant practical engineering unit for wire sizing and conductor specifications. 1 A/mm² = 10⁶ A/m². Safe operating limits vary by application: building wire 3-4 A/mm²; transformer windings 2-4 A/mm²; motor windings 4-8 A/mm² (with forced cooling); bus bars 1-2 A/mm² (continuous). These limits ensure temperature rise stays within insulation ratings.

Ampere per square centimeter (A/cm²) – Common in electrochemistry, battery technology, and semiconductor work. 1 A/cm² = 10⁴ A/m² = 0.01 A/mm². Electrode current density in batteries, fuel cells, and electrolysis cells is typically specified in mA/cm² to A/cm². Solar cell current output is often given in mA/cm².

Ampere per circular mil (A/cmil) – Traditional US wire industry unit based on the circular mil area (diameter in mils, squared). Used in National Electrical Code (NEC) ampacity tables and AWG specifications. The 変換係数 1 A/mm² ≈ 1973 A/cmil connects international and US systems.