Okay, let's break this down. You're asking about the sizing of the equipment grounding conductor (EGC) for a mini-split installation where the breaker size might be larger than the wire size feeding the load. Here's the relevant information and how it applies to your situation

Key Concepts & NEC Sections
Overcurrent Protection (Breaker/Fuse)

This protects the circuit conductors (hot and neutral) from overloads and short circuits. Its size is based on the ampacity of the smallest conductor it protects (with some exceptions).

Equipment Grounding Conductor (EGC)

This provides a low-impedance path back to the source (service equipment) to facilitate the operation of the overcurrent protective device in case of a ground fault. Its size is related to the rating of the overcurrent device protecting the circuit.

NEC 250.122: Size of Equipment Grounding Conductors

This is the primary section that governs EGC sizing. It states that the EGC size is based on the rating of the overcurrent protective device protecting the circuit conductors.

NEC 240.4(D): Small Conductors

This section restricts the overcurrent protection for certain small conductors (#14 AWG copper, #12 AWG copper, #10 AWG copper) UNLESS certain exceptions apply.

Your Situation and Analysis

You have: Mini-split installed #12 AWG conductors feeding the mini-split 25 Amp breaker protecting the circuitThe Problem

NEC 240.4(D) limits the overcurrent protection for #12 AWG copper wire to 20 amps unless certain exceptions apply. So putting it on a 25 amp breaker may be a violation.

EGC Sizing Based on Breaker Size (NEC 250.122)

The size of the EGC is determined by the rating of the overcurrent device protecting the circuit. So, if you're using a 25 amp breaker, you need to consult NEC Table 250.122 to find the minimum size EGC required.

Using NEC Table 250.122

If the overcurrent protective device is 25 amps, Table 250.122 requires a #12 AWG copper EGC.

The 75% Tap Rule/Exception

The 75% tap rule and other exceptions you're thinking of generally apply to reducing the size of conductors after an overcurrent device in very specific situations like motor circuits. This does not apply to the size of the EGC.

Summary and Recommendations1. Compliance

According to Table 250.122 your EGC should be #12 copper.
2.

Addressing the 25 Amp Breaker

The main issue is if you use a 25 amp breaker on #12 wire. If this is a violation of 240.4(D) you will need to address it and the appropriate size breaker may affect your EGC sizing.
3.

Consult the Mini-Split's Instructions

Crucially, check the manufacturer's installation instructions for the mini-split. They may specify the minimum circuit ampacity and the maximum overcurrent protection device allowed. They may also call for a specific wire size. If the instructions allow for a 25 amp breaker, follow those instructions. The instructions will usually be followed as that equipment is UL listed with those instructions

Important Considerations



Local Amendments

Your local jurisdiction may have amendments to the NEC. Always check with your local electrical inspector to ensure compliance with local codes.

Safety

Electrical work can be dangerous. If you are not comfortable working with electricity, hire a qualified electrician.

Documentation

Keep all documentation related to the installation, including the mini-split's installation instructions, for future reference and inspection purposes.

In Conclusion

While a #10 AWG EGC is not required, the 25 amp breaker may be a violation of 240.4(D) if there are no applicable exceptions.Disclaimer: I am an AI chatbot and cannot provide professional electrical advice. This information is for general guidance only. Always consult with a qualified and licensed electrician for specific electrical installations and to ensure compliance with all applicable codes and regulations. Flag for review