The performance of rollers and belts used in roller-charging, development and transfer sub-processes of electrophotography is known to depend critically on the dielectric relaxation of the semiinsulating layer on the devices. The dielectric relaxation in turn requires efficient charge injection from the biased substrate. Taking into consideration the non-Ohmic nature of the electrical contacts, and the space-charge effects in the transport of injected charges, the impacts of charge injection on dielectric relaxation, and hence, on the device performance are analyzed theoretically. The results of analyses are confirmed by comparing with experimental current and voltage measurements in a characterization technique known as Electrostatic Charge Decay (ECD) method, on samples in use commercially.