When to use: Use whenever installing branch circuits, feeders, or service entrance equipment. NEC Article 250 covers two distinct grounding conductors:
EGC (Equipment Grounding Conductor): Runs in the same raceway as circuit conductors. Sized per NEC Table 250.122 based on the overcurrent protective device rating. Provides a fault return path.
GEC (Grounding Electrode Conductor): Connects the neutral/service to earth (ground rod, building steel, etc.). Sized per NEC Table 250.66 based on the largest service conductor.
This tool sizes equipment grounding conductors (EGC) and grounding electrode conductors (GEC) per NEC Article 250. Electrical engineers and inspectors use it to verify that grounding conductors are correctly sized for every branch circuit, feeder, and service entrance installation.
NEC Article 250 defines two distinct grounding functions. The EGC (Equipment Grounding Conductor) provides a low-impedance fault return path within the electrical system, ensuring the overcurrent protective device (OCPD) operates before dangerous touch voltages develop. EGC size is determined by the OCPD rating using NEC Table 250.122 — a 200A circuit breaker requires a #6 AWG copper EGC, while a 400A breaker requires a #3 AWG copper EGC.
The GEC (Grounding Electrode Conductor) connects the neutral/service entrance to the grounding electrode system (ground rods, concrete-encased electrode, building steel, or ground ring). GEC size is determined by the largest service entrance conductor per NEC Table 250.66. A 350 kcmil service requires a #2 AWG copper GEC.
Ground electrode resistance per IEEE 80/142 should be ≤25 ohms for a single ground rod, or ≤5 ohms for critical facilities. Soil resistivity (measured in ohm-meters) drives the number of ground rods or the length of ground ring required.
NEC Article 250 is the primary governing code for grounding and bonding of electrical systems in the United States, covering system grounding (250.20–250.36), equipment grounding (250.110–250.148), grounding electrode systems (250.50–250.68), and bonding (250.90–250.104). IEEE 80 governs grounding of ac substations. IEEE 142 (Green Book) provides recommended practice for grounding of industrial and commercial power systems. NFPA 780 covers lightning protection grounding. For telecommunications, TIA-607 specifies bonding and grounding.
The EGC must be continuous — no switches, fuses, or disconnecting means in the grounding path. Where conductors are increased in size for voltage drop, the EGC must be proportionally increased (NEC 250.122(B)). For aluminum EGC, the minimum size is always one size larger than copper due to lower conductivity.
The grounding electrode system must include all available electrodes: concrete-encased electrodes (Ufer ground), building steel, metal water pipe, ground rings, and driven ground rods. Ground rods must be at least 8 feet long and separated by at least 6 feet (NEC 250.56). The concrete-encased electrode (minimum 20 ft of #4 AWG copper in the footing) is the most effective electrode and is required whenever a new concrete foundation is poured.
Select the conductor material (copper or aluminum), then enter the OCPD rating protecting the circuit for EGC sizing — the tool looks up NEC Table 250.122 and returns the minimum conductor size. For GEC sizing, select the size category matching your largest service entrance conductor — the tool returns the minimum GEC size from NEC Table 250.66. Use both results together on every service entrance installation.
The EGC runs inside the raceway with the circuit conductors and provides the fault current return path back to the source (bonded neutral) to ensure the OCPD trips. The GEC is a single conductor from the service entrance neutral/ground bar to the earth electrode — it provides the connection to earth but is not intended to carry fault current.
No. NEC 250.142 prohibits using the grounded (neutral) conductor as the EGC on the load side of the service disconnect, except in specific cases like ranges, dryers (250.140), and separately derived systems. The EGC must be a separate conductor.
A concrete-encased electrode (Ufer ground) consists of at least 20 feet of #4 AWG or larger copper conductor or 1/2 inch rebar encased in concrete at the bottom of a foundation. Concrete has high moisture content and good electrical contact with soil, achieving very low resistance — often under 1 ohm — making it the most effective grounding electrode per IEEE 142.
NEC 250.56 requires that if a single 8-foot ground rod does not achieve 25 ohms or less, a second rod must be added at least 6 feet away. Most AHJs require two rods as a standard practice. For critical facilities (data centers, hospitals), soil resistivity measurement and multiple rods or a ground ring are recommended to achieve ≤5 ohms.
When ungrounded conductors are increased in size beyond the minimum required ampacity (for example, for voltage drop compensation), the EGC must be proportionally increased per NEC 250.122(B). Multiply the required EGC area by the ratio of the actual conductor area to the minimum required area.
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