The motor size is selected out of the available standard sizes, taking the maximum power draw of the compressors at the design point into consideration, as well as derating factors, such as ambient temperatures and installation altitude. If you require an extra minimum security buffer, or additional spare motor power for future upgrades, you can select this at the performance input form under the tab 'Settings'. Please note: choosing a higher motor size than required will let the motor run in off-design conditions and will reduce its efficiency the further you operate away from design point. We recommend to set the minimum security to zero (0). The actual buffer is visible at the result page, between power draw at design point and chosen motor size.