You've highlighted a very valid and commonly debated point regarding the application of 250.122(B) and voltage drop considerations for equipment grounding conductors (EGCs). Your reasoning and examples are spot on – the percentage increase for small circuits can lead to oversized EGCs that don't seem practically necessary for fault current clearing.Let's break down the issues and potential solutions

The Core Problem:
Overly Conservative Application

Applying the voltage drop percentage increase literally to small EGCs (#12, #10) results in sizes that are often far larger than required to handle the available fault current.

Technical Violation

Relying solely on Table 250.122 after accounting for voltage drop on the ungrounded conductors is technically a violation of 250.122(B).

Logical Disconnect

The logic behind 250.122(B) is to ensure adequate EGC impedance for effective fault clearing, but applying it rigidly can lead to sizes disproportionate to the actual fault current.

The "Equipment Grounding" Focus

As you correctly pointed out, the EGC's primary function is to provide a low-impedance path back to the source during a fault at the equipment. The fault current, influenced more by the available fault current from the source and the total impedance of the fault path, not just the voltage drop percentage.

Why 250.122(B) Exists (and Why it's Important, Generally)



Impedance Matters

Increasing the size of the EGC does reduce its impedance. Lower impedance means higher fault current and faster breaker tripping, which is vital for safety.

Coordination with OCPD

The EGC must be sized to handle the available fault current until the overcurrent protective device (OCPD) operates.

Mitigation of Touch Potential

A low-impedance EGC path helps to minimize the voltage rise (touch potential) on metal enclosures during a ground fault.

Longer Runs, Higher Impedance

As circuit length increases, so does impedance, and this is what 250.122(B) attempts to address.

Why Your Concerns are Valid



Diminishing Returns

The reduction in impedance by significantly oversizing a small EGC (e.g., going from #12 to #6) provides a diminishing return in terms of fault current clearing speed, especially if other factors (transformer impedance, source impedance) are limiting the available fault current.

Cost and Practicality

Oversized EGCs increase material costs and make installations more difficult.

Misinterpretation

The intent of 250.122(B) is often misunderstood, leading to overly conservative designs.

Possible Solutions and Language Considerations

Here are a few approaches to addressing this issue, ranging from the practical to code change proposals:1.

Careful Impedance Calculation (Most Technically Correct, Most Difficult)

The most rigorous approach is to actually calculate the impedance of the entire fault current path, including the source impedance, transformer impedance, conductor impedance (phase and EGC), and connection impedances. This is complex and requires detailed knowledge of the power system. You can then verify that the EGC is adequately sized to handle the available fault current based on the OCPD's trip curve. This rarely done.2.

Documentation and Justification (Currently Legal, Requires Engineer Stamp)

An Engineer of Record, in the documents, can justify using a smaller EGC than dictated by the code because of specific characteristics of the installation.3.

Code Change Proposal (Long-Term Solution)

This is the most impactful but also the most challenging. Your proposed language is a good starting point. Here are a few refinements:

Option 1 (Clearer Language)

"Where ungrounded conductors are increased in size to compensate for voltage drop, equipment grounding conductors shall be increased in size proportionately, according to the circular mil area of the ungrounded conductors. However, the equipment grounding conductor size shall not be required to exceed the size determined by Table 250.122 based on the rating of the overcurrent protective device protecting the circuit, unless required for effective ground fault clearing as determined by an engineering study."



Option 2 (Focus on Impedance)

"Where ungrounded conductors are increased in size to compensate for voltage drop, equipment grounding conductors shall be increased in size proportionately, according to the circular mil area of the ungrounded conductors, unless an engineering study demonstrates that the equipment grounding conductor size determined by Table 250.122 provides adequate impedance to ensure effective ground fault clearing in accordance with Section 110.
10."

Option 3 (Introduce a Threshold)

"Where ungrounded conductors are increased in size to compensate for voltage drop, equipment grounding conductors shall be increased in size proportionately, according to the circular mil area of the ungrounded conductors. However, this increase is not required for circuits using conductors #10 AWG and smaller, provided the equipment grounding conductor is sized per Table 250.122." (This is a simpler, more practical approach, but less technically rigorous.)

Explanation of Language Choices



"Engineering Study"

This places the onus on a qualified individual to perform the necessary calculations and analysis. It provides a pathway for using smaller EGCs when justified, but also requires accountability.

"Effective Ground Fault Clearing in Accordance with Section 110.10"

This ties the requirement back to the NEC's fundamental rule about interrupting fault current safely.

"Provides Adequate Impedance"

Focuses on the real goal, not just an arbitrary percentage increase.

"Circuits Using Conductors #10 AWG and Smaller"

A simple blanket exemption for the small circuits where the problem is most pronounced.

Important Considerations for a Code Change Proposal



Substantiation

You'll need strong technical justification, including calculations, simulations, and real-world examples to demonstrate the problem and the safety of your proposed solution.

Collaboration

Work with other engineers, contractors, and industry experts to refine your proposal and gain support.

NEC Process

Understand the NEC code-making process and submit your proposal through the proper channels.

Practical Recommendations



Document, Document, Document

If you're designing a system with oversized phase conductors due to voltage drop and are using a smaller EGC than 250.122(B) dictates, document your reasoning and calculations thoroughly. This provides justification for your design.

Communicate

Discuss your approach with the inspector and AHJ. Explain your reasoning and be prepared to provide supporting documentation.

Consult with a PE: If you're unsure, consult with a licensed professional engineer who can perform the necessary calculations and provide guidance.In conclusion, your concerns are valid, and the current wording of 250.122(B) can lead to overly conservative designs. While there isn't a universally accepted workaround, careful impedance calculations, proper documentation, communication, and a potential code change proposal are all viable paths forward. Good luck! Flag for review