- Grounding Conductor Definition: A grounding conductor is defined as a wire intentionally connected to the earth, often referred to as a “ground conductor” or “case ground”.
- Safety Purpose: The primary function of the grounding conductor is to offer a safe path for fault currents, preventing electrical hazards by diverting current away from people and equipment.
- Grounded vs. Grounding: Understanding the difference between “grounding” and “grounded” conductors is crucial; the former relates to earth connection for safety, while the latter completes the electrical circuit.
- Color Identification: Grounding conductors can be recognized by their color—either green or green with yellow stripes, according to various international standards.
- Calculation Basics: When sizing a grounding conductor, it should be at least 25% of the phase conductor’s capacity, an essential basic electrical knowledge for safety in installations.
What is a Grounding Conductor?
A grounding conductor is a wire or bar earthed on purpose, called the equipment grounding conductor (EGC) in US practice, and also a ground wire or case ground.
The EGC is bonded to the metal case of a box, appliance or tool, also called a case ground.
The grounding conductor is a safety path. In normal service it carries no load current.
If a live part touches the case, the EGC is a low-resistance return so fault current can flow back to the source and trip the overcurrent device.
That current should go through the EGC, not through a person. The case voltage during the fault is still I times the impedance of that path, so the device must open quickly.
Do not mix this with the grounded conductor. In the NEC that term is the grounded circuit conductor, usually the neutral.
People also say grounded conductor or neutral. That wire carries load current in normal service. The EGC does not.
The neutral returns normal load current. The EGC returns fault current only.
What Color Wire is a Grounding Conductor?
An EGC may be bare, covered or insulated. If it is insulated or marked, US practice uses green or green with a yellow stripe. IEC PE identification is green-and-yellow.
IEC 60445 (which replaced IEC 60446), AS/NZS 3000 and BS 7671 identify the protective earth as green-and-yellow.
Older practice in some countries used green only. Canada (CEC) now allows green or green with yellow. Always follow the code that applies at the installation.
How to Calculate the Size of a Grounding Conductor
The EGC is a low-impedance fault current path. It holds the case near earth potential only if that path is short and the protective device opens.
A shop thumb rule sizes the EGC at least 25% of the phase conductor or overcurrent-device rating. NEC does not use that percentage.
NFPA 70 (NEC) Table 250.122 sets the minimum EGC size from the rating of the overcurrent device ahead of the equipment. The stored table below follows that list. If you upsize the phase conductors, NEC 250.122(B) may require a larger EGC.
| NEC Table 250.122 | ||
| Rating or setting of automatic overcurrent device in the circuit ahead of equipment, conduit, etc. Not Exceeding (Ampere) | Size (AWG or kcmil) | |
| Copper | Aluminum or copper-clad aluminum | |
| 15 | 14 | 12 |
| 20 | 12 | 10 |
| 60 | 10 | 8 |
| 100 | 8 | 6 |
| 200 | 6 | 4 |
| 300 | 4 | 2 |
| 400 | 3 | 1 |
| 500 | 2 | 1/0 |
| 600 | 1 | 2/0 |
| 800 | 1/0 | 3/0 |
| 1000 | 2/0 | 4/0 |
| 1200 | 3/0 | 250 |
| 1600 | 4/0 | 350 |
| 2000 | 250 | 400 |
| 2500 | 350 | 600 |
| 3000 | 400 | 600 |
| 4000 | 500 | 750 |
| 5000 | 700 | 1200 |
| 6000 | 800 | 1200 |
