Which type of meter must carry the entire load current through the meter?

The type of meter that must carry the entire load current through the meter is the self-contained meter. This meter is designed to directly measure the electrical consumption of a circuit by allowing the full load current to flow through it. Self-contained meters are typically used for residential or small commercial applications where the current level is low enough to be handled by the meter itself without any additional transforming equipment.

In contrast, other types of meters, such as two-part meters, digital meters, and smart meters, may not directly handle the load current. For instance, two-part meters might utilize a current transformer to manage higher load currents, meaning that only a fraction of the current passes through the meter for measurement. Digital and smart meters can also be designed to work with current transformers, especially in cases where the load is higher than what the meter can safely measure directly.

Understanding the operational fundamentals of these different meter types is essential for linemen, as it informs decisions around installation and application, especially in terms of safety and accuracy in measuring electrical usage.