What is the minimum size of rigid metal conduit for a commercial service rated at 150 A, 120/240 V single-phase using THWN wire?

To determine the minimum size of rigid metal conduit for a commercial service rated at 150 A, 120/240 V single-phase using THWN wire, it’s important to consider the number of conductors and their sizes that will be housed within the conduit.

For a 150 A service with THWN wire, you typically use conductors that are at least #2 AWG copper or #1 AWG aluminum, which can handle the current load. According to the National Electrical Code (NEC) guidelines, the appropriate conduit size must accommodate not just the wires themselves but also provide sufficient space for proper heat dissipation and to allow for easy installation.

Conduit fill tables provided in the NEC indicate the maximum number of conductors permissible for different sizes of conduit. In the case of using #2 AWG THWN copper conductors, a 1 1/2 inch rigid metal conduit is generally accepted as the minimum size. It provides adequate space for the conductors, ensuring that they do not exceed the allowable fill, which is crucial for safety and code compliance.

Using a smaller conduit could result in overcrowding, leading to potential overheating and increased resistance in the conductors, which could cause issues like tripped breakers or damage to the wiring