The output of a step down transformer is measured to be 24v

The turns ratio is expressed with two numbers, like 2:1 or 2 to 1. The first number represents the primary's relative number of turns, while the second number represents the secondary's relative number of turns. The turns ratio of a transformer is calculated by applying the following formula: $$\fracturns$$ This type of transformer is normally furnished with coil taps at multiples of 2.5% above normal (AN) and 2.5% below normal (BN). For a primary with 1620 turns, 2.5% represents about 40 turns (1620 × 0.025 = 40.5). Moving the connection by two tap locations changes the number of turns in the primary coil by about 80 turns. The primary is changed from 1620 turns to 1540 turns. The turns ratio is changed so that the transformer can compensate for the low voltage and ensure that the secondary is at the rated voltage.