The ground wire provides a safety path for electrical current in fault conditions, protecting equipment and personnel from shock hazards. Typically colored green or bare copper, the ground wire connects equipment frames, enclosures, and metal raceways to the main ground bus at the service panel. This path carries current only during short circuits or ground faults.
Technical Details
Ground wire size is determined by the overcurrent protection device rating per NEC Table 250.122. For a 15-amp breaker, 14 AWG ground wire is acceptable, while 20-amp circuits require 12 AWG minimum. The ground resistance to earth should not exceed 25 ohms for most installations. Ground wires connect to the neutral bus only at the main service entrance; all other locations require separate ground and neutral conductors.
Practical Significance in HVAC
Proper grounding prevents electrical shock when touching equipment during maintenance. HVAC condensing units, air handlers, and control transformers must be grounded to meet NEC requirements and manufacturer specifications. Testing grounding continuity with a multimeter is essential before energizing new HVAC installations to verify safety compliance.