A solar technician is performing a ground continuity test on a newly installed PV array. They measure the resistance between the module frames and the main grounding electrode conductor (GEC). What is the maximum allowable resistance for this connection to be considered adequately grounded, according to common industry standards and best practices for safety?
- A0.1 Ohm
- B1 Ohm
- C25 Ohms
- D5 Ohms
Show answer & explanationAnswer & explanation
Correct answer: B. 1 Ohm
While the NEC specifies requirements for the grounding electrode system resistance (typically 25 Ohms or less for the earth connection), for equipment grounding continuity (resistance between accessible metal parts and the GEC), industry best practices and testing standards often recommend a maximum resistance of 1 Ohm or less to ensure an effective fault current path and minimize shock hazard. This ensures that in the event of a fault, the circuit breaker will trip effectively.
Why the other options are wrong
- A. 0.1 Ohm is extremely stringent and often difficult to achieve in practice.
- C. 25 Ohms is the NEC maximum for the *grounding electrode resistance to earth*, not for the continuity of the equipment grounding path itself.
- D. 5 Ohms is acceptable for some larger grounding electrode systems but generally too high for equipment bonding continuity.
PV Equipment Grounding Continuity
The low-resistance electrical connection between all non-current-carrying metal parts of a PV system and the equipment grounding conductor, ensuring a safe path for fault currents.
- Critical for electric shock prevention.
- Industry best practice: ≤ 1 Ohm.
- Ensures effective operation of overcurrent protection devices.
Memory trick: Equipment ground: One Ohm or less, for safety's best success.