Quick Hits

🗓️ MAY 16, 2026
⚡ GROUNDING & BONDING — EP 6

When NEC REQUIRES a System to Be Grounded (NEC 250.20)
joshthesparky4 · Josh The Sparky

Opening Hook
⚡ Not every electrical system is required to be grounded.
A lot of electricians assume ALL systems must be grounded — but NEC 250.20 says otherwise.

Episode Overview
Quick breakdown of when the NEC REQUIRES AC systems to be grounded, why certain systems are exempt, and how grounding requirements depend on system voltage and configuration.

Core Idea
⚡ System grounding is based on electrical characteristics — not preference
• Some systems are required to be grounded
• Some are permitted to remain ungrounded
• Some require special grounding methods
👉 The NEC determines this based on voltage-to-ground and system type

Code Breakdown
NEC 250.20 — AC Systems to Be Grounded
• Systems operating at less than 50V may still require grounding under certain conditions
• 50V–1000V systems are grounded when they meet specific NEC conditions
• Common grounded systems include:
• 120/240V single-phase systems
• 208Y/120V three-phase systems
• 480Y/277V systems
👉 If one conductor can intentionally reference ground, NEC usually requires grounding

Common Exceptions & Special Cases
• Separately derived systems follow additional rules
• Certain industrial systems may operate ungrounded for continuity purposes
• High-impedance grounded systems use specialized fault limiting methods
👉 Grounding requirements change depending on the system design

Why It Matters
⚡ Grounded systems help stabilize voltage to earth
⚡ Grounding improves fault detection and overcurrent device operation
🔥 Incorrect assumptions lead to code violations and troubleshooting confusion
⚠️ Understanding grounding type changes how faults behave

Common Field Mistakes
• Assuming every transformer secondary must be grounded
• Confusing bonding with grounding
• Misidentifying grounded conductors vs equipment grounding conductors
• Believing “grounded” means “safe from shock”

Core Takeaways
• NEC 250.20 determines when grounding is required
• System voltage and configuration matter
• Grounding affects fault behavior and system stability
• Bonding and grounding are NOT the same thing

Final Takeaway
The NEC doesn’t ground systems “just because.” ⚡
Grounding requirements exist because system behavior changes dramatically depending on how the electrical system references earth.

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