What is an arc-fault circuit interrupter (AFCI) designed to do?
- Detect small leakage currents that could shock a person
- Limit the voltage delivered to sensitive electronics
- Detect arcing in wiring and shut the circuit off
- Switch the house to backup power during an outage
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C. Detect arcing in wiring and shut the circuit off
An AFCI recognises the electrical signature of arcing, such as at a damaged cable or loose connection, and opens the circuit before it starts a fire. Detecting leakage current to protect people is what a GFCI does.
Reference: Electrical: AFCI operating principle (NEC 2023 210.12, concept)
In a panel, two branch circuit wires are clamped under the single screw of one breaker that is not designed for two wires. What is this defect called and why does it matter?
- A backfeed; the breaker is being fed power from its load side
- A bootleg ground; the neutral is now tied to the ground
- A double tap; the wires may be loose and can overheat
- A split bus; the breaker now feeds two different voltages
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C. A double tap; the wires may be loose and can overheat
Most breaker terminals are listed for one conductor. Two wires under one screw may not be clamped evenly, which leads to a loose connection, arcing and heat. Some breakers are specifically designed and marked for two conductors.
Reference: NEC 2023 110.14(A) (terminals for more than one conductor)
What is the largest fuse or breaker that normally protects a 12 AWG copper branch circuit conductor?
- 15 amps
- 20 amps
- 30 amps
- 40 amps
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B. 20 amps
The small-conductor rule limits 14 AWG copper to 15 amps, 12 AWG to 20 amps and 10 AWG to 30 amps. A 30-amp breaker on 12 AWG wire is over-fusing and lets the wire overheat.
Reference: NEC 2023 240.4(D) (small conductors)