Capacitance of a transmission line is the result of the potential difference between the conductors; it causes them to be charged in the same manner as the plates of a capacitor when there is a potential difference between them. The capacitance between conductors is the charge per unit of potential difference. Capacitance between parallel conductors is a constant depending on the size and spacing of the conductors. For power lines less than about 80 km (50 mi) long, the effect of capacitance can be slight and is often neglected. For longer lines of higher voltage capacitance becomes increasingly important.