Master Electrician Exam (NEC)Special Occupancies, Equipment, and ConditionsMedium
A master electrician is installing a new data processing system in a commercial office building. The system requires a dedicated branch circuit. According to NEC, what is the minimum size of the grounding conductor for a 20-ampere branch circuit supplying data processing equipment, if the circuit conductors are No. 12 AWG copper?
- ANo. 14 AWG copper
- BNo. 10 AWG copper
- CNo. 12 AWG copper
- DNo. 8 AWG copper
Show answer & explanationAnswer & explanation
Correct answer: C. No. 12 AWG copper
NEC Table 250.122 specifies the minimum size of equipment grounding conductors. For a 20-ampere overcurrent protective device, the minimum size for a copper equipment grounding conductor is No. 12 AWG. This applies generally and also to data processing systems unless specific conditions require larger sizes.
Why the other options are wrong
- A. No. 14 AWG copper is typically for 15-ampere circuits, not adequate for a 20-ampere circuit.
- B. No. 10 AWG copper is larger than the minimum required for a 20-ampere circuit, typically used for 60-ampere OCPD.
- D. No. 8 AWG copper is significantly larger than necessary for a 20-ampere circuit, typically used for 100-ampere OCPD.
Data Processing EGC Sizing
The minimum size of the equipment grounding conductor for dedicated branch circuits supplying data processing equipment, determined by the circuit's overcurrent protective device rating.
- Follows general EGC sizing rules (NEC 250.122).
- Critical for sensitive electronic equipment.
- Ensures proper fault current path.
Memory trick: Circuit's OCPD sets the EGC's pace, Table 250.122, no guessing case!