Ground Wire Size Calculator — EGC and GEC

Two different answers, because a 200 A service involves two different grounding conductors. The equipment grounding conductor for a 200 A overcurrent device is 6 AWG copper from Table 250.122. The grounding electrode conductor depends on the service conductors — for typical 2/0 or 3/0 copper it is 4 AWG copper from Table 250.66, but if the only electrode is a driven ground rod, 250.66(A) caps it at 6 AWG. People arguing about "4 or 6" are usually both right about different conductors.

An equipment grounding conductor is the fault-return path: it bonds metal enclosures back to the source so a ground fault has a low-impedance route that trips the breaker. It is sized from the overcurrent device rating (Table 250.122), because its job is to carry fault current long enough to open that device. A grounding electrode conductor connects the system to earth — lightning, static, and voltage stabilisation. It is sized from the service-entrance conductors (Table 250.66). Different jobs, different tables, and neither substitutes for the other.

No, and it is normally much smaller. An equipment grounding conductor only carries current during a fault, for the fraction of a second before the breaker opens — so it is sized for that brief duty, not for continuous load. A 200 A feeder on 3/0 copper takes only a 6 AWG EGC. The exception is when the ungrounded conductors are upsized, which triggers 250.122(B).

Because NEC 250.66(A) says the portion of a grounding electrode conductor that is the sole connection to a rod, pipe, or plate electrode need not be larger than 6 AWG copper. The logic is that the rod itself is the limiting factor — a driven rod's contact resistance with the earth is measured in ohms, so a conductor larger than 6 AWG cannot improve the connection. Similar caps exist at 4 AWG for concrete-encased electrodes (250.66(B)) and at the ring size for a ground ring (250.66(C)).

Yes, with restrictions. Both tables list aluminum sizes. But NEC 250.64(A) prohibits aluminum or copper-clad aluminum grounding electrode conductors in direct contact with masonry or earth, or where subject to corrosive conditions, and requires them to be kept at least 18 inches above earth when used outdoors. In practice most GECs are copper for exactly this reason.

Yes. NEC 250.122(B) requires the EGC to be increased proportionally whenever the ungrounded conductors are increased in size — and it does not matter why you increased them. The ratio is by circular mils. If 12 AWG (6,530 cmil) goes to 8 AWG (16,510 cmil) for voltage drop, that is a factor of 2.53, so a 12 AWG EGC scales to 16,510 cmil and becomes 8 AWG. Toggle the upsize option above to run this. See the Voltage Drop Calculator for when upsizing is needed.

No. The neutral is a grounded conductor — it carries normal unbalanced load current as part of the circuit. A grounding conductor carries current only during a fault. They are bonded together at exactly one point, the service disconnect, and must be kept separate everywhere downstream (NEC 250.24(A)(5) and 250.142). Bonding neutral to ground in a subpanel is one of the most common and most serious wiring errors, because it puts load current onto the grounding system.