preventive maintenance
routine service and upkeep performed to avoid development of future problems. failure or breakdowns.
primary (primary line)
in an electric utility system. a high-voltage distdbution electric supply line. usually 2.400 to 34.500 volts. that carries electricity from distribution substations to distribution transformers.
primary elements
nitrogen (N). phosphorus (P). and potassium (K . lncluded in various ratios in fertilizer (see essential elements. macronutrient. and micronutrient).