When you search for an NEC ground wire size chart PDF, you are looking for one specific table in the National Electrical Code: Table 250.122. This table dictates the minimum size for your Equipment Grounding Conductor (EGC) based entirely on the rating of the overcurrent protective device (the breaker or fuse) protecting the circuit.
For the most common residential circuits, here is your quick-jump answer for copper wire: a 15A breaker requires 14 AWG; a 20A breaker requires 12 AWG; a 30A breaker requires 10 AWG; a 50A breaker requires 10 AWG; a 100A feeder requires 8 AWG; and a 200A service requires 4 AWG. If you need the exact values for aluminum, larger feeders, or edge cases, read on.
How to Read the NEC Ground Wire Size Chart (Table 250.122)
The most common mistake apprentices and DIYers make is trying to size the ground wire using the same temperature columns (60°C, 75°C, 90°C) they use for hot and neutral wires in NEC Table 310.16. Do not do this.
Table 250.122 does not care about the insulation temperature rating of your ground wire. The EGC's job is not to carry continuous load current; its job is to safely carry a massive, momentary fault current back to the source to trip the breaker. Therefore, the only column that matters is the rating of the overcurrent device (the breaker or fuse size). You simply find your breaker size in the first column, then move right to select either the Copper or Aluminum/Clad Aluminum column based on the wire material you are pulling.
Note: Bare copper is the standard for EGCs in residential NM-B (Romex) and THHN in conduit. Aluminum EGCs are rarely used in residential branch circuits but are common in large commercial feeders due to cost and weight savings.
The Complete NEC Equipment Grounding Conductor Sizing Table
Below is the complete data set derived directly from NFPA 70 (National Electrical Code) Table 250.122. Bookmark this section for quick jobsite lookups.
| Overcurrent Device Rating (Amps) | Copper Wire Size (AWG/kcmil) | Aluminum Wire Size (AWG/kcmil) | Common Residential/Commercial Application |
|---|---|---|---|
| 15A | 14 AWG | 12 AWG | Standard lighting & receptacles |
| 20A | 12 AWG | 10 AWG | Kitchen/bath small appliance circuits |
| 30A | 10 AWG | 8 AWG | Dryers, water heaters, RV outlets |
| 40A | 10 AWG | 8 AWG | Cooktops, EV chargers (Level 2) |
| 50A | 10 AWG | 8 AWG | Ranges, hot tubs, 50A RV pedestals |
| 60A | 10 AWG | 8 AWG | Subpanel feeds (small shed/garage) |
| 70A - 90A | 8 AWG | 6 AWG | Medium subpanels, heavy machinery |
| 100A | 8 AWG | 6 AWG | Standard 100A subpanel feeder |
| 110A - 125A | 6 AWG | 4 AWG | Large subpanels |
| 150A | 6 AWG | 4 AWG | Large residential subpanels |
| 175A | 4 AWG | 2 AWG | Commercial feeders |
| 200A | 4 AWG | 2 AWG | Standard 200A main residential service |
| 225A - 250A | 3 AWG | 1 AWG | Large residential / light commercial |
| 300A | 2 AWG | 1/0 AWG | Commercial service entrance |
| 350A - 400A | 1 AWG | 2/0 AWG | Heavy commercial / industrial feeders |
Source: NFPA 70, National Electrical Code (NEC), Table 250.122. Always consult the latest adopted edition in your local jurisdiction.
What the Chart Cannot Tell You: Derating and Edge Cases
While the PDF chart gives you the baseline, real-world jobsite conditions often force you to deviate from the table. Here is how derating and physical constraints modify your base ground wire size.
Parallel Conductor Runs: If you are running parallel feeders (e.g., two sets of 350 kcmil for a 600A service), NEC 250.122(F) requires an equipment grounding conductor in every raceway or cable assembly. You do not divide the ground wire size; each parallel run gets a full-sized EGC based on the rating of the overcurrent device protecting that specific parallel set.
Ambient Temperature and Bundling: Unlike current-carrying conductors, the EGC does not carry continuous load, so it is generally exempt from the ambient temperature and bundling derating factors found in NEC 310.15. However, if you are forced to upsize your hot wires to compensate for bundling derating, the proportional upsizing rule for the ground wire kicks in again.
Frequently Asked Questions (FAQ)
Can I use a smaller ground wire if my actual electrical load is very low?
No. The NEC ground wire size chart sizes the EGC based on the overcurrent protective device rating, not the actual calculated load. If you have a 5A continuous load (like a well pump) but it is protected by a 30A breaker (due to motor starting surge requirements), you must use a 10 AWG copper ground wire. The breaker dictates the maximum fault current the ground must survive, not the running amperage of the appliance.
What size ground wire do I need for a 200 amp residential service?
For a standard 200A residential main service or subpanel feeder, Table 250.122 requires a minimum of 4 AWG bare copper or 2 AWG aluminum. If you are using 4/0-4/0-2/0-4/0 aluminum mobile home feeder cable (often called 4/0 MH feeder), the built-in ground is 4 AWG aluminum, which is explicitly permitted by the code for 200A residential services despite the table calling for 2 AWG.
Does this NEC ground wire size chart PDF apply to DC solar and battery systems?
Yes and no. For the AC output side of your inverter, Table 250.122 applies perfectly based on the AC breaker size. However, for the DC side (solar panels to charge controller, or battery bank to inverter), you must follow Article 690 and Article 480. DC fault currents behave differently, and battery-to-inverter cables often require massive grounding conductors (sometimes matching the size of the DC power cables, like 2/0 or 4/0) to handle the immense short-circuit current a lithium or lead-acid bank can deliver before the fuse clears.
Can I use the metal conduit (EMT/IMC) as my ground wire instead of pulling a wire?
Under NEC 250.118, properly installed and bonded rigid metal conduit (RMC), intermediate metal conduit (IMC), and electrical metallic tubing (EMT) are approved as an Equipment Grounding Conductor. However, many local AHJs (Authorities Having Jurisdiction) and commercial specs require a separate, pulled copper EGC inside the conduit regardless of the raceway type. For DIY and residential flexible metal conduit (FMC) or MC cable, you must pull a separate ground wire or rely on the internal bare wire/bonding strip provided by the manufacturer.
