The force that causes a current to move through some resistance, in this case, the National Grid. In industry terms, electricity moves round the main grid at a high voltage. When it is stepped down to the level of a smaller grid or an actual site it is regarded as low voltage. Low voltage supply is more expensive because of the costly process of stepping it down from high voltage. A number of larger industrial sites take high voltage direct which means they incur the cost of stepping the voltage down. For this, they subsequently receive more competitive pricing.