Grounding vs Bonding

The two jobs

Grounding and bonding work together, but they are not the same job. The exam knows candidates blur the terms. It will describe a rod, a raceway, a panel, a breaker, or a service conductor and wait for you to reach for the wrong table.

• Grounding: connects the system to earth through the grounding electrode system.
• Bonding: connects metal parts together so a fault has a low-impedance path back to the source.
• GEC: grounding electrode conductor. Think service to electrode. Usually Table 250.66.
• EGC: equipment grounding conductor. Think circuit fault path. Table 250.122.
• Bonding jumper: connects metal parts when the raceway or equipment path needs a deliberate bond.

GEC vs EGC

The grounding electrode conductor and equipment grounding conductor are the two names you need cold. They sound similar. They answer different questions.

• GEC follows the service conductor. It connects to the grounding electrode system and is commonly sized from Table 250.66.
• EGC follows the breaker. It runs with branch-circuit or feeder conductors and is sized from Table 250.122.
• The input is different. GEC looks at service conductor size. EGC looks at overcurrent device rating.

If you want the deeper GEC table walk-through, use the NEC 250.66 GEC guide.

Worked example: 200 amp service and a 60 amp feeder

A service has 2/0 copper ungrounded service conductors. A separate 60 amp feeder leaves a panel and needs an equipment grounding conductor. Which sizing tables do you use?

1. For the grounding electrode conductor at the service, ask what it connects to. It connects the service to the grounding electrode system.
2. That is a GEC question. Use Table 250.66, based on the service conductor size.
3. For the feeder equipment grounding conductor, ask what it follows. It follows the feeder overcurrent device.
4. That is an EGC question. Use Table 250.122, based on the 60 amp overcurrent device.
5. Do not use Table 250.66 for the feeder EGC. Do not use Table 250.122 for the service GEC.

Wrong answers the exam wants you to pick

Using Table 250.122 for a GEC

Table 250.122 follows the overcurrent device. A grounding electrode conductor does not get sized from the branch breaker.

Using Table 250.66 for an EGC

Table 250.66 follows service conductor size. An equipment grounding conductor for a feeder or branch circuit follows the OCPD.

Forgetting electrode caps

Some electrodes do not require a larger GEC past a certain point. Rod, pipe, plate, concrete-encased, and water-pipe electrodes have details candidates miss because they stop at the table row.

How to drill this for the exam

For every Article 250 question, write three words before the table: job, input, table. If the job is electrode, the input is service conductor size. If the job is circuit fault path, the input is the breaker. That habit prevents most grounding and bonding misses.