For a 120/240-volt load, which connection should be used from the transformer?

In a 120/240-volt system, the appropriate connection to use from the transformer is a center-tapped transformer configuration. This setup provides two 120-volt sources with a common neutral, allowing for both 120-volt and 240-volt circuits.

The center tap serves as the neutral point, allowing the voltage across the two outer taps to be 240 volts. When one loads a single tap with a 120-volt appliance, the circuit effectively draws power from one side of the transformer to the center tap, providing the necessary voltage. This enables flexibility in the use of electrical appliances, as both 120-volt and 240-volt devices can be connected to the system.

This configuration is standard for residential and light commercial applications, aligning with common practices in electrical design and installation. It allows effective distribution of voltage and is commonly used in both new installations and upgrades. The correct connection reflects the principles of voltage distribution and practical application within the NEC (National Electrical Code) standards.