The flow of electrons through a conductive material, down a potential gradient from high to low concentration, generates electricity. The potential gradient, or the difference between the high and low concentration of electrons, represents the voltage and may vary depending on the electrical source. Electrical injuries can be separated based on low-voltage or high-voltage injuries, where a threshold of either 500 V to 100 V may be used. This is considered high. Household electricity in the United States is set at 110 V, though some high-power appliances may be set as high as 240 V. In comparison, industrial and high-tension electrical power lines can be set at greater than 100,000 V.