A fault inside a metal box turns that enclosure live until something gives the current a low-resistance path home. That path is the bare copper grounding conductor, and it exists for the seconds when a hot conductor touches metal it shouldn’t. Bare copper serves two jobs in U.S. wiring: as an equipment grounding conductor (EGC) that clears faults, or as a grounding electrode conductor (GEC) that ties your system to earth — same wire, two roles, two sizing rules.
Equipment Grounding Conductor vs. Grounding Electrode Conductor
An EGC clears faults; a GEC connects the system to the grounding electrode. Mixing up their sizing tables is one of the most common code errors in residential and light commercial work.
- EGC: Runs alongside circuit conductors from panel to outlet, box, or appliance frame, carrying fault current during a short circuit so the breaker opens before someone gets shocked.
- GEC: Connects the grounded service conductor to the grounding electrode system — ground rods, metal water pipe, ground ring, or concrete-encased electrode. It stabilizes system voltage and handles lightning and surge energy, but does not clear branch-circuit faults on its own.
- Bonding jumpers: Short bare copper runs tying metal parts together — gas piping near the panel, metal raceways, structural steel — so they stay at the same potential.
EGCs are sized off the overcurrent device rating using NEC Table 250.122; GECs are sized off the largest service or feeder conductor using NEC Table 250.66. Pull the wrong table and you’ll either undersize the conductor or waste copper.
| Wire Role | Sizing Basis | Current Carry |
|---|---|---|
| Equipment grounding conductor (EGC) | NEC Table 250.122, by overcurrent device rating | Fault current only |
| Grounding electrode conductor (GEC) | NEC Table 250.66, by largest service conductor | Fault, surge, and earth reference |
| Bonding jumper | Per NEC 250.102 based on conductor size | Equalizes potential only |
| Concrete-encased electrode (Ufer) | Minimum 20 ft of bare copper, 4 AWG or larger | Earth reference via foundation steel |
| Ground ring | Minimum 2 AWG bare copper, 20 ft min, 30 in deep | Earth reference and surge dissipation |
How Bare Copper Ground Wire Actually Works
Under normal conditions the bare copper carries zero current, sitting at zero volts until a fault happens. When a hot conductor faults to a bonded metal enclosure, the bare copper provides a low-impedance path back to the source, allowing large fault current to flow that the breaker or fuse detects and opens within a fraction of a second. The lower the impedance, the faster the trip — which is why connection quality at every terminal and box matters as much as wire gauge.
In the GEC role, the conductor bonds the grounded conductor to earth through ground rods, a ground ring, or a concrete-encased electrode, giving the system a stable voltage reference and a path for lightning and surge energy — but it isn’t sized to clear a branch-circuit fault.
Common Mistakes and Code Limits
Bare copper is code-permitted in most grounding roles, but never a substitute for a hot conductor or a neutral. Treating it as general-purpose current-carrying wire is a violation and a safety problem.
- Confusing the two sizing tables — EGCs follow NEC Table 250.122, GECs follow NEC Table 250.66.
- Skipping the Ufer minimums — NEC 250.52(A)(3) requires at least 20 ft of bare copper no smaller than 4 AWG for a concrete-encased electrode.
- Undersizing a ground ring — 2 AWG minimum, at least 20 ft, buried 30 in or deeper.
- Assuming all bare copper is interchangeable — service equipment, feeders, and electrodes each carry their own minimums.
- Ignoring physical damage and corrosion — bare copper exposed to abrasion, chemicals, or wet locations may need protection or a different conductor type.
- Forgetting local amendments — jurisdictions adopt specific NEC editions whose amendments can change which installations are approved.
Matching gauge and material to the right NEC table is the deciding factor. For a residential or shop build, our rounded-up guide to the best bare copper ground wire breaks down sizes and applications side by side.
The NEC permits EGCs to be bare, covered, or insulated, and bare is explicitly allowed. The University of Michigan’s design guide and ACE Power’s wiring reference both spell out these identification and installation requirements in detail.
FAQs
Can bare copper ground wire carry current?
Only during a fault. Under normal operation it should sit at zero current and zero volts, waiting to carry fault current back to the source if a hot conductor touches bonded metal. Using it as a regular current-carrying conductor violates the National Electrical Code and creates a real shock hazard.
Is bare copper always allowed for grounding?
Bare copper is explicitly permitted for equipment grounding conductors and commonly used for grounding electrode conductors and bonding jumpers. Specific contexts — like conductors 6 AWG and smaller on the equipment grounding side — may require green marking or insulation, so check the local code edition and amendments before installation.
Why do EGCs and GECs use different sizing tables?
They do different jobs. The EGC only needs to carry fault current long enough to trip a breaker, so it’s sized by the overcurrent device rating. The GEC ties the system to earth and handles surge energy, so it’s sized by the largest service conductor feeding the system.
References & Sources
- University of Michigan Architecture, Engineering and Construction. “Design Guideline: Grounding and Bonding (Section 26).” Supports grounding conductor roles and installation requirements.
- ACE Power. “Wiring Guide.” Supports conductor identification and grounding practice details.
- Electrical License Renewal. “NEC Continuing Education: Grounding and Bonding.” Supports NEC Tables 250.122 and 250.66 sizing rules and Ufer electrode minimums.
