In most European countries the rule is rather simple. You're allowed a total of 4.5% voltage drop from the service fuses but not more than 1.5% at the meter, that leaves you with 3% to the very end of the longest circuit. Your grid operator is responsible for supplying a voltage that keeps your appliances within limits if you stick to the 3% rule. VOltage drop is always calculated at full nominal circuit load, i.e. the size of the supplying fuse/breaker. The only exception to this rule are circuits that only supply one hard-wired load, usually a motor, which requires a larger fuse/breaker to account for startup inrush and the motor is protected by a thermal cutout.
