Resistance: $R_{DC} = \rho \frac{L}{A}$ where $\rho_{Cu} \approx 1.724 \times 10^{-8} \, \Omega \cdot m$ at $20^\circ C$.

Temperature Coefficient: $R_T = R_{20} [1 + \alpha (T - 20)]$.

Skin Effect (AC): For AC, skin depth $\delta = \sqrt{\frac{\rho}{\pi f \mu}}$. The AC resistance ratio $k_{ac}$ increases $R_{DC}$.

Ampacity: Estimated using standard convection/radiation balancing $I = \sqrt{\frac{h \cdot A_{surf} \cdot \Delta T}{R_{ac}}}$, often simplified using empirical DIN 43671 or IEC standards.