A method based on single-particle tests has been developed to characterise the pre-weakening effect of high voltage pulses on ores. A pre-weakening index, PWI, defined as the percentage change in ore breakage resistance indicator (A*b) per unit of specific energy, is used to evaluate the energy efficiency of an electrical comminution machine, and to assess an ore's amenability to pre-weakening by high voltage pulses. A reduced JKRBT (JK Rotary Breakage Tester) testing procedure using five tests (instead of the standard 12 tests per sample) to determine the ore breakage parameters, makes characterisation by high voltage pulse pre-weakening more practical. A gold-copper ore sample treated by high voltage pulses, based on single-particle tests with a specific energy of 1.6 kWh/t, achieved an A*b change from 31 to 84 at a nominal particle size of 30 mm, representing a 171% pre-weakening result. X-ray tomography images show the induced cracks/microcracks in the pulses-treated rocks. The pre-weakening effect was found more pronounced for larger fragments, suggesting that the use of high voltage pulses to pre-weaken AG/SAG mill feed may result in more significant benefits in terms of energy savings or increased throughput than pre-weakening ball mill feed. (C) 2013 Elsevier Ltd. All rights reserved.