The physics
A current heats a resistor. The heat each second is the power.
P = V I = I² R = V² / R H = I² R t
A rating gives an appliance's power at one voltage. Its resistance is R = V² / P. It stays the same on other voltages.
In a line, the same current flows through each part. So the bigger resistance takes more power. Side by side, each part gets the full voltage. So the smaller resistance takes more power.
Appliances in a house sit side by side, so their powers add. A fuse melts when the current goes above its rating.
I = P / V 1 kWh = 3.6 × 10⁶ J
A power line wastes I²R as heat. The same power at a higher voltage needs less current. So the line loses less.