Just to clarify, it's all 110/120V service. The 50/30/20 amp rating is simply how many amps are available for use of your devices. 15/20 amp service is a standard household plug, 30 amp is the next step connecting all devices to a total of 30 amps and 50 amp service provides 2 separate 50 amp legs for a total of 100 amps available for use but more than 50 amps on either leg will trip the combined breaker.
220/240 V service is not used but rather 2 separate 120 V legs. Yes, 240 V can be measured at the breaker box but is not used in that manner.