T/F: peak demand as sum of class peaks

FALSE.

The peak demand of a load centre is the coincident (simultaneous) maximum of the combined load, not the arithmetic sum of the class peaks.

Justification:

• Different consumer classes reach their maximum demand at different hours. Domestic load peaks in the evening (lighting, cooking), commercial load around midday/afternoon, and offices, schools and institutions during working hours.
• At the hour of the load centre peak, each class draws only a fraction of its own peak. This fraction is the contribution (responsibility) factor $c_i$.
• Therefore

$$P_{LC} = \sum c_i \, P_{class,i} \le \sum P_{class,i}$$

Example: domestic peak 20 kW (evening, $c = 1$), commercial peak 6 kW ($c = 0.5$ in the evening), institutional peak 4 kW ($c = 0.1$):

$$P_{LC} = 20 + 3 + 0.4 = 23.4 \text{ kW, not } 30 \text{ kW}$$

Adding the class peaks directly would oversize the distribution transformer and feeders, raising capital cost and no-load losses. The plain sum is correct only if all classes peak at the same time (all contribution factors equal to 1), which rarely happens.