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⚡ Code Corner: 🔸 NEC 705.11(D) & (F) – Source Connections: Conductor Length Limits

Sharpen your knowledge with a quick dive into the NEC.

Author

Chris Martinez
June 20, 2025

🔌 What it says:
When connecting power production sources (like PV systems, batteries, or generators) to a panel-board:

  • 🔹 705.11(D): Source conductors must be as short as practical, not exceeding 10 feet, unless protected per NEC tap rules.

  • 🔹 705.11(F): This 10-foot rule does not apply if the source connects to a dedicated power production panel-board that doesn't serve any loads.

🧯 Why It Matters:

Long, unprotected source conductors increase the risk of arc faults or fire during short circuits. This rule ensures safe interconnections—especially when back-feeding a busbar.

💡 Pro Tip: When designing renewable or backup systems, locate the power source disconnect and panel-board close together to stay under the 10’ rule. It saves on labor, material, and inspection delays.

❓ Quick Code Quiz: “Too Far or Just Right?”

Question:
You’re connecting a battery energy storage system to a main panel. The source conductors will run 12 feet from the battery disconnect to the panel-board, which also feeds loads.

According to NEC 705.11(D), is this installation compliant?

Choose the correct answer:

A. Yes — as long as the conductors are in EMT
B. No — the conductors exceed the 10 ft limit
C. Yes — if the panel is labeled “Power Production”
D. No — you must use SE cable instead

Answer below 👇

🧠 Think It Through:

You’re tying in a 15kW solar inverter to a load center 12 feet away.

❌ No. According to NEC 2020, source conductors to a load-serving panel-board must be 10 feet or less unless:

  • They are protected in accordance with tap rules (e.g., NEC 240.21), or

  • They terminate in a dedicated power production panel-board that serves no loads (705.11(F)).

✅ Answer: B. No — the conductors exceed the 10 ft limit

📘 Reference: NEC 2020 – Article 705.11(D) & (F):

705.11(D) – Conductor Length: “The conductors shall not exceed 10 ft (3 m) in length in dwelling units or 5 m (16.5 ft) in other occupancies unless protected in accordance with 240.21 or connected to a dedicated power production panel-board.”

705.11(F) – Dedicated Panel-board Exception: “This length limitation shall not apply if the panel-board does not supply any loads and is used only for interconnection of power production sources, provided that overcurrent protection and labeling are still met.”