Electrician's Licensing Practice Exam

How is the number of receptacles on a 20-amp circuit determined for residential applications?

1. Based on the total amperes

2. The NEC provides specific guidance

3. It's based on box fill

4. By calculating between 1 and 1.5 amperes per receptacle

The correct answer is: It's based on box fill

In residential applications, the number of receptacles on a 20-amp circuit is influenced by the box fill requirements established by the National Electrical Code (NEC). Box fill refers to the amount of space that electrical conductors and devices occupy in a junction box, which is critical for ensuring that there is adequate room for heat dissipation and to prevent overcrowding that can lead to safety hazards. The NEC specifies that each receptacle outlet counts as a certain volume in terms of box fill calculations, and this includes various factors such as the size of the box, the number of conductors, and the types of devices mounted in the box. Therefore, to determine how many receptacles can safely be installed on a circuit without exceeding the maximum fill capacity of a box, electricians must follow these box fill rules. The reasoning involving amperes, specific NEC guidance for overall circuit load, or the average current per receptacle does not directly dictate a maximum number of receptacles, but rather, they are factors that ensure the circuit is not overloaded and operates safely. While there are guidelines related to amperage, they do not provide a direct formula for how many receptacles can be present on a circuit—this is where box fill considerations come into play.