Grounding & Bonding
The system that keeps non-current-carrying metal at earth potential and gives fault current a low-impedance path back to the source.
Why this code exists
Ungrounded systems left equipment enclosures energized during a fault. Grounding and bonding ensure breakers trip and surfaces stay safe to touch.
Article 250 is one of the most-referenced articles in the code, defining the grounding electrode system, equipment grounding conductors, and bonding of metal parts so a ground fault becomes a short circuit the overcurrent device can clear.
When it applies
Article 250 governs every installation. Any time you have metal that could become energized during a fault, you are bonding it and providing a low-impedance return path so the overcurrent device can clear quickly.
Common mistakes
- Confusing grounding with bonding. Bonding ties metal together; the earth connection alone will not trip a breaker.
- Relying on the equipment grounding conductor as if it carried normal current. It is a fault path, not a neutral.
- Undersizing the equipment grounding conductor relative to the overcurrent device ahead of it.
In the field
On an industrial retrofit I traced a nuisance-trip complaint to a broken bonding jumper across a flex fitting. The fault path was running through conduit couplings with high impedance, so the breaker held long enough to energize a machine frame. I installed a proper bonding jumper, the impedance dropped, and the next fault cleared instantly. That is the whole point of the article: give current the fast, deliberate route home.
Grounding and bonding is where I slow down the most. Get the fault path wrong and the breaker never trips — the metal just sits there waiting.
See full history
- 1913 — Grounding provisions formalized.
- 2002 — Article reorganized for clarity.
Related codes
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