Electrical Wiring Basics
88 flashcards by MentisLibrary
How residential wiring actually works: panels and branch circuits, wire gauge and ampacity, grounding versus bonding, GFCI and AFCI protection, and the code requirements behind each one. Safe practice is built into the cards, not bolted on.
- What is voltage, in practical terms?
- Electrical pressure, the difference in potential that pushes current through a circuit. Measured in volts.
- What is current, and what unit is it measured in?
- Current is the rate of flow of electric charge through a conductor, measured in amperes (amps).
- What is resistance?
- Opposition to current flow, measured in ohms. Higher resistance means less current for the same voltage.
- State Ohm's law and its three forms.
- E = I times R. Rearranged: I = E divided by R, and R = E divided by I.
- How do you calculate power in a single phase AC circuit?
- P = E times I, watts equal volts times amps. With power factor, P = E times I times PF.
- What is the difference between AC and DC?
- DC flows in one direction at a steady polarity. AC reverses direction periodically, which is what utility power supplies.
- What does a residential 120/240 V single phase service actually deliver?
- Two ungrounded (hot) legs at 240 V between them, and 120 V from either leg to the grounded neutral.
- Name the main components of a residential service entrance.
- Service drop or lateral, service point, meter socket, service entrance conductors, service disconnect or main breaker, and the grounding electrode system.
- What does the main bonding jumper do?
- It connects the grounded (neutral) conductor to the equipment grounding system and enclosure at the service, and only at the service.
- In a subpanel, how are neutrals and grounds handled?
- They are kept separate: the neutral bar is isolated from the enclosure, and equipment grounding conductors land on a separate bonded ground bar.
- What is a branch circuit?
- The conductors between the final overcurrent device and the outlets it supplies.
- What is the actual purpose of a circuit breaker or fuse?
- To protect the conductors and equipment from overcurrent so the wiring never overheats. It is not primarily there to protect people.
- How does a common thermal magnetic breaker trip?
- Two mechanisms: a bimetal strip that bends on sustained overload, and a magnetic element that trips almost instantly on a high fault current.
- What is the 80 percent rule for continuous loads?
- A circuit supplying a continuous load (3 hours or more) should be loaded to no more than 80 percent of the breaker rating.
- What does a GFCI do, and at what leakage level does it trip?
- It compares current leaving on the hot with current returning on the neutral and opens when the difference reaches roughly 4 to 6 mA.
- What does an AFCI do?
- It detects the electrical signature of an arcing fault, such as a damaged cord or a nicked conductor, and opens the circuit to prevent fire.
- What is the difference between a GFCI and an AFCI?
- A GFCI protects people from shock by detecting current leaking to ground. An AFCI protects property from fire by detecting arcing faults.
- A GFCI keeps tripping on a circuit. What is the correct response?
- Diagnose the leakage: check for moisture in outdoor boxes, a failing appliance, a shared or crossed neutral, or long runs with high capacitive leakage.
- A breaker trips repeatedly. Why is installing a larger breaker the wrong fix?
- Because the breaker protects the wire. A larger breaker lets the existing conductors carry current beyond their ampacity, which is a fire hazard.
- How does AWG numbering work?
- American Wire Gauge runs backwards: the smaller the number, the larger the conductor. 14 AWG is smaller than 12 AWG, which is smaller than 10 AWG.
- What copper conductor size and breaker go together for a standard 15 A circuit?
- 14 AWG copper on a 15 A overcurrent device.
- What copper conductor size goes with a 20 A branch circuit?
- 12 AWG copper, protected at 20 A.
- What copper conductor size goes with a 30 A circuit?
- 10 AWG copper, protected at 30 A. A typical electric dryer circuit is 30 A with 10 AWG.
- What is the 60 C ampacity of 8 AWG and 6 AWG copper, and why does that matter for NM-B?
- 8 AWG copper is 40 A and 6 AWG copper is 55 A at 60 C. NM-B is limited to the 60 C column, so a 50 A range circuit in NM-B needs 6 AWG.
- Why does the termination temperature rating limit ampacity?
- The whole circuit is limited by its weakest thermal link. Most breakers and lugs are listed for 60 C or 75 C terminations even when the wire insulation is 90 C.
- How does aluminum compare to copper for conductors?
- Aluminum has higher resistance per unit size, so for the same ampacity aluminum is typically about two AWG sizes larger than copper.
- What must you do differently when terminating aluminum conductors?
- Use terminals and devices listed for aluminum (AL/CU or CO/ALR), apply the listed antioxidant compound where required, and torque to the manufacturer's specification.
- What is THHN, and where is it used?
- A single conductor building wire with thermoplastic heat resistant nylon coated insulation, rated 90 C dry. It is pulled into conduit, not run exposed.
- What is NM-B cable, commonly called Romex?
- A nonmetallic sheathed cable with two or more insulated conductors plus a bare equipment grounding conductor, for dry interior locations.
- What is UF cable and where is it used?
- Underground Feeder cable, a solid molded jacket cable rated for direct burial and wet locations.