What is the maximum allowable overcurrent protection for NM cables installed without spacing?

The maximum allowable overcurrent protection for non-metallic (NM) cables installed without spacing is 15 amperes. This limit is established to ensure safety and prevent overheating of the cables, which can occur if the current exceeds the conductor's capacity. NM cables are designed to handle specific loads, and proper overcurrent protection is crucial to avoid damage to the insulation and reduce the risk of fire hazards.

When NM cables are installed without spacing—meaning they are bundled closely together without any air circulation—the heat generated by the current flow has a more challenging time dissipating. Consequently, overcurrent protection devices must be set at levels that will not allow the cables to exceed their temperature ratings, ensuring safe operation. The 15-amp limit provides a balance between permitting sufficient load while maintaining safety standards in residential wiring systems.

Other overcurrent protection options like 20 or 25 amperes would exceed the safe operating conditions for NM cables installed in such a manner, which is why they are not appropriate for this situation.