Grounding and Bonding Room
Grounding connects the system to earth. Bonding ties metal parts together so a fault clears. The exam mixes them on purpose. The grounding electrode conductor sizes from Table 250.66. The equipment grounding conductor sizes from Table 250.122. Different tables, different inputs. Get those two straight and Article 250 stops being a trap.
Last reviewed June 2026 · Staff Answer
Which table sizes the grounding electrode conductor?
Pick an answer to see the work and why each wrong choice traps people.
What this room is for
- Separating grounding from bonding once and for all
- Knowing which table sizes which conductor
- Catching the upsize rule when phase conductors grow
What not to post
- Requesting quoted NEC text. Article numbers only.
- Claiming a question came from a real exam.
- Posting anything that identifies you publicly.
Answered questions in this room
Grounding electrode conductor vs equipment grounding conductor: which table sizes which?
The grounding electrode conductor sizes from Table 250.66, based on the largest ungrounded service conductor. The equipment grounding conductor sizes from Table 250.122, based on the overcurrent device ahead of the circuit. Different tables, different inputs. The exam swaps them on purpose, so anchor each one to its table.
What size grounding electrode conductor do I need?
Size it from Table 250.66 off your largest ungrounded service conductor. There is one shortcut worth memorizing: the part of the conductor run to a single ground rod, pipe, or plate never needs to be larger than 6 AWG copper, no matter how big the service. For the rest, read the table by service size.
Room FAQ
What is the Grounding and Bonding Room?
Grounding connects the system to earth. Bonding ties metal parts together so a fault clears. The exam mixes them on purpose. The grounding electrode conductor sizes from Table 250.66. The equipment grounding conductor sizes from Table 250.122. Different tables, different inputs. Get those two straight and Article 250 stops being a trap.
What should I do first in this room?
Start with the daily drill. Pick an answer before reading the explanation, then read why the wrong choices trap candidates.
When should I take the full diagnostic?
Take the full diagnostic when you are not sure which NEC area is costing you points, or when the same miss shows up more than once.
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