If you are trying to figure out how to size ground for 200 amp service, the direct answer depends on which specific ground wire you are pulling. For the main Grounding Electrode Conductor (GEC) connecting your panel to the earth ground rods or water pipe, you need 4 AWG bare copper. For a 200-amp Equipment Grounding Conductor (EGC) running from the main panel to a subpanel, you need 6 AWG copper or 4 AWG aluminum.

Confusing these two conductors is the most common mistake DIYers make when upgrading to a 200-amp service. Sizing them incorrectly doesn't just fail inspection; it creates a lethal touch-potential hazard. Below is the hazard-first breakdown, the exact decision table for your wire picks, and the verification steps to prove your grounding system actually works.

The Hazard: What Happens When a 200A Service Ground Fails?

CRITICAL HAZARD: An undersized or high-impedance ground wire prevents the main breaker from tripping during a line-to-ground fault. This leaves the metal panel chassis energized at 120V or 240V, creating a lethal touch-potential shock risk for anyone who touches the panel while grounded.

To understand why wire size matters, you have to look at the physics of a fault. When a 240V hot wire breaks loose and touches the metal panel chassis, the grounding wire provides the path back to the source. The massive surge of current (fault current) traveling through this path is what triggers the magnetic trip mechanism inside your 200-amp main breaker, shutting off the power in milliseconds.

If your ground wire is undersized, its electrical impedance (resistance to AC current) is too high. According to Ohm's Law ($I = V / Z$), high impedance restricts the fault current. Instead of a massive 2,000-amp surge that instantly trips the breaker, you might only get 40 amps of fault current. The breaker's thermal overload might eventually trip after 30 seconds, but by then, the undersized ground wire has melted inside the wall, and the panel chassis has been sitting at a lethal voltage the entire time. Furthermore, high-impedance ground faults generate intense localized heat, leading to electrical fires inside the panel or junction boxes.

Ground vs. Neutral vs. Bond: Clearing the Confusion

Before pulling wire, you must separate three terms that are frequently (and incorrectly) used interchangeably on hardware store aisles:

  • Neutral (Grounded Conductor): The white or gray wire. This is a current-carrying conductor designed to handle the normal return current of your 120V circuits back to the transformer.
  • Ground (Equipment Grounding Conductor - EGC): The bare or green wire. This is a non-current-carrying conductor under normal conditions. It exists solely to carry massive fault current during a short circuit to trip the breaker.
  • Bond (Main Bonding Jumper): The physical metal bridge (or screw) that connects the neutral bar to the ground bar. In a 200-amp main service panel, the neutral and ground must be bonded. In a subpanel, they must never be bonded.

When you 'size the ground,' you are sizing the safety net (EGC/GEC), not the normal return path (Neutral). For a 200A service, your neutral and hot wires are typically 2/0 AWG copper or 4/0 AWG aluminum. The ground wires are sized relative to these massive ungrounded conductors.

The Decision Table: Sizing Your 200-Amp Ground Wires

Use this decision tree to select the exact wire gauge and material for your specific 200-amp grounding scenario. These values are derived from standard NEC-style guidance (Tables 250.66 and 250.122). Always verify with your local Authority Having Jurisdiction (AHJ), as local amendments can override baseline tables.

Scenario / Conductor Type Purpose Copper Size (Min) Aluminum Size (Min) NEC Reference
Grounding Electrode Conductor (GEC) Connects main panel ground bus to ground rods, ufer, or metal water pipe. 4 AWG (Concrete Pick) 2 AWG Table 250.66 (Based on 2/0 Cu or 4/0 Al service conductors)
Equipment Grounding Conductor (EGC) - Feeder Runs inside a 200A feeder cable from main panel to a 200A subpanel. 6 AWG 4 AWG Table 250.122 (Based on 200A OCPD rating)
Main Bonding Jumper Internal bridge connecting neutral bar to ground bar in the main service disconnect. 2/0 AWG (or equivalent cross-sectional area) 4/0 AWG Table 250.28(B) (Must match largest service conductor)
Grounding Ring / Rod Wire Connecting multiple 8-foot ground rods together in a daisy chain. 4 AWG (Match GEC) 2 AWG 250.53(F)
Bench Tip: If you are pulling a 200A feeder to a detached garage subpanel, do not use the 4 AWG GEC wire for your EGC. While 4 AWG is larger than the required 6 AWG EGC (which is fine electrically), bare wire inside a conduit with hot conductors can cause abrasion issues, and pulling bare wire through long conduit runs is a physical nightmare. Use 6 AWG insulated green THHN for the subpanel EGC, and save the 4 AWG bare copper for the exterior ground rods.

Step-by-Step: Terminating and Verifying the Grounding System

Sizing the wire correctly is only half the job. A 4 AWG ground wire with a loose lug connection has the same high-impedance failure mode as a 14 AWG wire. Follow these steps to terminate and verify your 200A grounding system.

  1. De-energize and Lock Out: If you are terminating wires inside the main service panel, the utility meter must be pulled to de-energize the service lugs. Never work on the line-side of a main breaker while it is energized.
  2. Strip and Seat the Conductor: Strip the 4 AWG bare copper GEC just enough to seat fully into the ground bar lug. Do not leave bare copper exposed outside the lug, and do not clip strands to make it fit. If the lug is too small, you are using the wrong panel or the wrong lug accessory.
  3. Torque to Specification: Use a calibrated torque screwdriver or torque wrench. Most modern panel ground bars require between 35 and 45 inch-pounds of torque for 4 AWG wire. Check the sticker inside your specific panel door (e.g., Square D Homeline or Eaton BR) for the exact value. Hand-tight is a code violation and a fire hazard.
  4. Drive and Clamp the Rods: Drive two 8-foot copper-bonded ground rods at least 6 feet apart. Use acorn-style ground clamps rated for direct burial. Tighten the clamps until the bolt snaps off (if using breakaway bolts) or torque to the manufacturer's spec (usually 25-30 ft-lbs).
  5. Verify with a Multimeter (Neutral-to-Ground Test): Once the system is re-energized and under a heavy load (turn on the oven, AC, and dryer), set your multimeter to AC Volts. Measure between the neutral bar and the ground bar. A properly sized and bonded 200A service should read less than 2.0V. If you read 5V or higher, you have high impedance, a loose neutral, or an illegal neutral-to-ground bond downstream in a subpanel.
  6. Verify with a Clamp Meter (Leakage Test): Clamp your meter around the 4 AWG GEC wire heading out to the ground rods. Under normal conditions, this should read 0.0A. If you read significant current (e.g., 2A+) on the earth ground wire, you have a parallel neutral path, meaning current is returning through the dirt or plumbing instead of your neutral wire.

For comprehensive testing methodologies, reference the Fluke guide on ground resistance testing, which details the fall-of-potential method used to verify the actual earth resistance is below the NEC-mandated 25 ohms.

When to Call a Licensed Electrician (and AHJ Code Caveats)

While understanding the theory and tables is essential for any competent DIYer or trade student, the physical execution of a 200-amp service upgrade crosses strict legal and safety boundaries.

When a Licensed Electrician is Required:
  • Meter Pulls and Service Entrance Work: Working on the line-side of the main breaker or pulling the utility meter requires utility authorization and a licensed professional. Arc flash incidents at the 200A service entrance carry explosive force and lethal heat.
  • Upgrading from 100A to 200A: Replacing the main service panel involves coordinating with the utility company, upgrading the service mast, and pulling new 2/0 or 4/0 service conductors from the weatherhead to the panel.
  • Trenching and Ufer Grounds: If your local code requires a concrete-encased electrode (Ufer ground) for new construction, this must be tied into the rebar before the foundation is poured, requiring coordination between the electrician and the concrete crew.

Finally, remember that the National Electrical Code (NEC) published by the National Fire Protection Association (NFPA) is a baseline standard, not federal law. Your local Authority Having Jurisdiction (AHJ)—usually the city or county electrical inspector—has the final legal authority. Some municipalities in high-lightning areas require 4 AWG GEC even for 100A services, while others mandate exothermic welding (Cadweld) instead of mechanical clamps for ground rod connections. Always pull a permit and review your local amendments before buying your copper wire.

By selecting 4 AWG bare copper for your GEC, 6 AWG copper for your 200A EGC feeders, and verifying the system with a multimeter under load, you ensure your 200-amp service provides a low-impedance path that will clear faults instantly, keeping your home and your life safe.