Master Electrician Exam (NEC)Overcurrent ProtectionEasy
A residential bathroom circuit feeds a single GFCI receptacle. If the circuit is rated for 20 amperes, what is the maximum leakage current that the GFCI device is designed to trip at, according to NEC requirements for personnel protection?
- A4 mA
- B5 mA
- C30 mA
- D6 mA
Show answer & explanationAnswer & explanation
Correct answer: B. 5 mA
NEC 210.8(A) and product standards specify that ground-fault circuit interrupters (GFCIs) for personnel protection must trip when the ground-fault current exceeds a nominal 5 milliamperes (mA).
Why the other options are wrong
- A. While a lower trip setting might offer more sensitive protection, 4mA is not the specified nominal trip level for GFCIs.
- C. 30mA is often associated with RCDs (Residual Current Devices) in other international standards, but not the nominal trip for U.S. GFCIs for personnel protection.
- D. This value is slightly above the nominal trip current and would not meet the required sensitivity.
GFCI Trip Level (Personnel)
A Ground-Fault Circuit Interrupter (GFCI) for personnel protection is designed to trip when a ground-fault current of 5 milliamperes (±1 mA) or more is detected, preventing electric shock.
- Nominal trip level is 5 mA.
- Protects against electric shock to humans.
- Required in specific locations like bathrooms, kitchens, outdoors.
Memory trick: GFCI is like a '5'-star bodyguard, always sensing a 'leak' to keep you safe.