The National Grid connects generating stations to consumers through cables and transformers. Step-up transformers increase transmission p.d.; step-down transformers reduce it for consumers. For the same transmitted power, higher p.d. means lower current, reducing cable heating losses because P_loss = I²R. Example: A line transmits 2000 W at 100 V. Calculate current. I = 2000 ÷ 100 = 20 A. Rearrange the relationship before substituting if a different quantity is required. Consider the conditions.