When measuring 110 AC voltage in a live circuit, where should the test probes from an AC voltmeter make contact?

Making contact across the line when measuring 110 AC voltage ensures that you are accurately assessing the voltage drop across the load in the circuit. This method provides a clear understanding of the operational voltage available at that point in the system. When probes are placed across the line, they measure the potential difference between two points in the circuit where the current is flowing, which is essential to determine whether the electrical components are functioning correctly and safely.

Measuring directly at the power source could yield the same voltage reading but doesn't necessarily reflect the voltage being delivered to a specific device or load in use. Testing at the circuit breaker helps assess protection but may not indicate how the voltage behaves under load conditions. Probing near the ground connection does not provide meaningful information about the voltage present in the circuit, as it doesn't measure the potential difference being used by the devices. Therefore, taking measurements across the line yields the most relevant information for ensuring proper circuit functioning.