What size AL EGC is needed for a feeder protected by fuses rated at 125 Amp?

For a feeder protected by fuses rated at 125 Amps, the appropriate size for an aluminum equipment ground conductor (EGC) can be determined by referencing the National Electrical Code (NEC) guidelines, specifically Table 250.122, which specifies the size of grounding conductors based on the rating of overcurrent protection devices.

When looking at the table, you will find that for a 125 Amp overcurrent protective device, the minimum size for an aluminum EGC is indeed 4 AWG. This size is determined to ensure that the ground conductor can effectively carry the fault current back to the source, promoting safety and reducing the risk of electrical hazards.

Choosing a conductor that is too small can result in overheating and potential failure during fault conditions, while a larger size could be unnecessarily costly and complicated for installation without offering additional benefits under typical circumstances. Therefore, 4 AWG aluminum is identified as the correct size for this application in compliance with the NEC requirements.