"Grounding" and "bonding" get used interchangeably on job sites, but NEC Article 250 treats them as two different jobs with two different conductors. Mixing them up is one of the most common sources of confusion when sizing service and feeder wiring.
Grounding connects your electrical system to the earth itself, through a grounding electrode such as a ground rod, metal water pipe, or concrete-encased electrode. Bonding connects metal parts — panel enclosures, raceways, equipment frames — together so that if a fault occurs, current has a low-impedance path back to the source and the overcurrent device trips quickly. Grounding deals with the earth; bonding deals with keeping metal parts electrically continuous with each other.
The Two Conductors, Side by Side
| Conductor | Job | Sized Per | Sized From |
|---|---|---|---|
| Grounding Electrode Conductor (GEC) | Ties service equipment to the earth (ground rods, water pipe, Ufer ground) | Table 250.66 | Service entrance conductor size |
| Equipment Grounding Conductor (EGC) | Carries fault current back to the panel to trip the breaker | Table 250.122 | Overcurrent device rating |
A third element, the main bonding jumper, ties the neutral bus to the enclosure and grounding system at the service — and only at the service. Bonding, by contrast to grounding, is generally about connecting metal parts to each other rather than to the earth.
Size Your Ground Wire Instantly
Enter your overcurrent device rating or service conductor size to get the correct GEC or EGC per Table 250.66 / 250.122.
Worked Example: A 200A Service with a Sub-Panel
A homeowner has a 200A main service and is feeding a detached garage sub-panel, also rated 200A. Two separate grounding-related conductors need to be sized:
- GEC (grounding, at the main service): With a standard 200A copper service entrance conductor, NEC Table 250.66 calls for a minimum 4 AWG copper grounding electrode conductor running from the service equipment to the ground rods or water pipe.
- EGC (bonding path, in the feeder to the sub-panel): Per NEC Table 250.122, a 200A overcurrent device requires a minimum 6 AWG copper (or 4 AWG aluminum) equipment grounding conductor run alongside the feeder conductors to the sub-panel.
Notice the two conductors land on different sizes — 4 AWG for the GEC, 6 AWG for the EGC — even though both are protecting the same 200A service. That's because one is sized from the service conductor size (Table 250.66) and the other from the overcurrent device rating (Table 250.122). Confusing the two tables is a common sizing mistake.
Key Rules to Remember
- Grounding ties to earth; bonding ties metal parts together. They serve different purposes even though both use similar-looking bare or green wire.
- Use the right table. GEC sizing always starts with Table 250.66 and your service conductor size. EGC sizing always starts with Table 250.122 and the breaker or fuse rating.
- Aluminum needs to be upsized. Aluminum grounding and bonding conductors must be one size larger than the copper equivalent, and terminations must be listed for aluminum use.
- Insulated EGCs must be green. If an equipment grounding conductor has insulation, it must be green or green with a yellow stripe — bare copper is also acceptable.
- The minimum is a floor, not a target. Both tables list minimum sizes; you can always install a larger grounding or bonding conductor than required.
Frequently Asked Questions
Is a ground wire the same thing as a bonding jumper?
No. A ground wire (the EGC) runs with a branch circuit or feeder and is sized per NEC Table 250.122. A bonding jumper is a separate conductor or fitting that connects metal parts — like the neutral bus to the enclosure at the service, or two sections of metal raceway — to guarantee a continuous, low-impedance path. They work together but are sized and installed differently.
What is the difference between a GEC and an EGC?
A Grounding Electrode Conductor (GEC) connects your service equipment to the grounding electrode system (ground rods, water pipe, concrete-encased electrode, etc.) and is sized per NEC Table 250.66 based on your service entrance conductor size. An Equipment Grounding Conductor (EGC) runs with each branch circuit or feeder to provide a fault return path and is sized per NEC Table 250.122 based on the overcurrent protection device rating.
What size are the GEC and EGC on a typical 200 amp panel?
For a 200A residential service, the GEC is typically 4 AWG copper per NEC Table 250.66 for standard 200A copper service entrance conductors. The EGC run to a 200A sub-panel is sized per Table 250.122 at a minimum of 6 AWG copper or 4 AWG aluminum. Two different tables, two different conductors, doing two different jobs.
Can aluminum wire be used for grounding and bonding?
Yes. The NEC permits aluminum for both equipment grounding conductors and grounding electrode conductors. Aluminum grounding conductors must be sized one step larger than the equivalent copper conductor to compensate for aluminum's lower conductivity, and all terminations must be listed for use with aluminum.
What color does an equipment grounding conductor have to be?
An EGC may be bare, covered, or insulated. If it is insulated, the NEC requires it to be green or green with one or more yellow stripes, so it is never mistaken for a current-carrying conductor.
Conclusion
Grounding and bonding accomplish different things, and the NEC gives each one its own table for a reason. When you're sizing a service or feeder, ask yourself which job the conductor is doing — tying the system to earth, or tying metal parts together — and pull the matching table: 250.66 for grounding electrode conductors, 250.122 for equipment grounding conductors.
Disclaimer: While our articles and tools are designed to align with the National Electrical Code, always check with local building inspectors and licensed electrical contractors before initiating physical installations.