How many 4 AWG, THW conductors can fit into an 18 in. section of 1 in. rigid metal conduit?

To determine how many 4 AWG THW conductors can fit into an 18-inch section of 1-inch rigid metal conduit, we must first look at the conduit fill requirements outlined in the National Electrical Code (NEC).

Rigid metal conduit has specific fill capacity limits to ensure safe and efficient installation. For 1-inch rigid metal conduit, the maximum number of conductors that can be accommodated depends on the size and insulation type of the conductors.

The NEC provides a fill table that specifies the maximum allowable fill for conduit based on the conductor size and the number of conductors. For 4 AWG THW conductors, it is common to find that a 1-inch conduit can safely hold up to 5 similar conductors without exceeding the fill limit. This limit considers factors such as heat dissipation and ease of pulling the conductors through the conduit.

In this case, since the given multiple-choice question indicates that 5 conductors can fit, this aligns with the NEC guidelines regarding conduit fill. The calculation reflects safe practices and code compliance, confirming the option of 5 conductors as the right selection.