- Ohm's law?
- E = I × R. Voltage (volts) equals current (amperes) times resistance (ohms). Rearranged: I = E ÷ R and R = E ÷ I.
- Power formula (DC / resistive)?
- P = E × I (watts). Also P = I² × R and P = E² ÷ R using Ohm's law.
- Single-phase AC power?
- P = E × I × PF, where PF is the power factor.
- Three-phase AC power?
- P = 1.732 × E × I × PF (the 1.732 is √3). Memorize 1.732.
- What is voltage?
- Electrical pressure (potential difference), measured in volts (E or V) — what pushes current through a circuit.
- What is current?
- The flow of electric charge, measured in amperes (I or A). Same everywhere in a series circuit.
- What is resistance?
- Opposition to current flow, measured in ohms (Ω). Adds in series; combines reciprocally in parallel.
- Series circuit — current rule?
- Current is the same through every component (one path).
- Series circuit — resistance rule?
- Resistances add: R = R₁ + R₂ + R₃.
- Series circuit — voltage rule?
- Voltage divides across the resistors (the drops add up to the source).
- Parallel circuit — voltage rule?
- Voltage is the same across every branch.
- Parallel circuit — resistance rule?
- 1/R = 1/R₁ + 1/R₂ + 1/R₃. Total is less than the smallest branch.
- Two equal resistors in parallel?
- Half the value of one (e.g., two 20 Ω in parallel = 10 Ω).
- Why are branch circuits wired in parallel?
- So each load gets full voltage and one failure doesn't kill the rest.
- Open in a series vs parallel circuit?
- Series: everything stops. Parallel: only that one branch stops.
- What is power factor?
- Ratio of real power (watts) to apparent power (volt-amperes). 1.0 (unity) = all power does useful work.
- Watts vs volt-amperes (VA)?
- Watts = real power (actual work). VA = apparent power. Power factor is the ratio between them.
- Single-phase vs three-phase?
- Single-phase: one alternating voltage (120/240 V dwellings). Three-phase: three voltages 120° apart, for larger loads.
- Common dwelling voltages?
- 120 V (lighting/receptacles) and 240 V (large appliances), from a 120/240 V single-phase service.
- What is voltage drop?
- Voltage lost along a conductor due to its resistance. Grows with longer runs, smaller wire, and more current.
- NEC voltage-drop recommendation?
- ≤3% on a branch circuit or feeder, ≤5% total. These are Informational Notes (recommendations), not enforceable rules.
- Single-phase voltage-drop formula?
- VD = (2 × K × I × L) ÷ CM. K ≈ 12.9 (copper), 21.2 (aluminum); L = one-way length (ft); CM = circular mils.
- Three-phase voltage-drop formula?
- VD = (1.732 × K × I × L) ÷ CM. Replace the 2 in the single-phase formula with 1.732.
- How to fix excessive voltage drop?
- Upsize the conductor (more circular mils = lower resistance = less drop).
- What does voltage drop do to equipment?
- Dims lights, slows and overheats motors, and wastes energy as heat in the conductor.
- Voltage-drop K constant (copper)?
- About 12.9 ohm-cmil/ft for copper (21.2 for aluminum).
- What is the NEC?
- The National Electrical Code (NFPA 70) — the model safety code, updated every 3 years, that journeyman exams are based on.
- Current NEC edition?
- The 2023 NEC (NFPA 70-2023). States adopt on a lag — many are still on the 2020 or 2017 edition.
- Electrical-plan symbol 'S3' means?
- A three-way switch — used in pairs to control one load from two locations.
- Electrical-plan symbol 'S4' means?
- A four-way switch — used between two three-way switches to control a load from three or more locations.
- What is a kilowatt-hour (kWh)?
- A unit of energy: 1,000 watts used for one hour. It's what the utility meter measures and bills.
- AC vs DC?
- AC (alternating current) reverses direction periodically (utility power, 60 Hz in the U.S.). DC (direct current) flows one way (batteries, electronics).
- U.S. line frequency?
- 60 hertz (Hz) — the AC voltage completes 60 cycles per second.
- What is impedance?
- Total opposition to AC current (resistance + reactance), measured in ohms. The AC counterpart of resistance.
- Conductor resistance vs size?
- Larger conductor (lower AWG number, more circular mils) = lower resistance = less voltage drop and heating.
- Kirchhoff's current law (concept)?
- Current into a junction equals current out of it — the basis for analyzing parallel branches.
- How does length affect voltage drop?
- Longer run = more resistance = more voltage drop (drop is proportional to length).
- Apparent vs real vs reactive power?
- Apparent (VA) is the total; real (W) does useful work; reactive (VAR) is stored/returned by inductors and capacitors.
- Convert horsepower to watts?
- 1 horsepower ≈ 746 watts. Motor nameplate HP × 746 ÷ (efficiency × PF) estimates input watts.
- Which carries the most questions: theory or code lookup?
- Calculations and code lookup. The exam is largely code-based and (in most states) open-book — speed at finding articles/tables matters.
- What is the service?
- The conductors and equipment that deliver electricity from the utility to a building's wiring (Article 230).
- Minimum service for a one-family dwelling?
- 100 amperes, three-wire.
- Service-entrance conductor ampacity?
- At least equal to the calculated load they supply.
- Dwelling 83% allowance?
- 120/240 V single-phase dwelling services and main feeders may be sized at 83% of the rating (dwelling services/feeders table, 310.12).
- What are service-entrance conductors?
- The conductors from the service point/meter to the service disconnecting means.
- Grounding (definition)?
- Connecting the electrical system to the earth through a grounding electrode conductor and electrode (Article 250).
- Bonding (definition)?
- Joining metal parts together so they're at the same potential — creates the low-impedance fault path that trips the breaker.
- Grounding vs bonding — what clears a fault?
- Bonding does (the EGC carries fault current back to the source). The earth does NOT clear faults.
- Grounding electrode conductor (GEC)?
- The conductor connecting the grounded system/equipment to the grounding electrode. Sized by Table 250.66.
- GEC max size to a ground rod?
- 6 AWG copper — never required to be larger, regardless of service size (made-electrode resistance limits the current).
- GEC max size to a concrete-encased (Ufer) electrode?
- 4 AWG copper — never required to be larger, regardless of service size.
- What is a grounding electrode?
- The conducting object making earth contact: ground rod, metal water pipe, concrete-encased (Ufer), or plate.
- What is a Ufer ground?
- A concrete-encased electrode — rebar or wire encased in the building's concrete footing/foundation.
- Equipment grounding conductor (EGC) — job?
- Bonds non-current-carrying metal back to the source, providing a low-impedance fault path so the breaker opens.
- EGC sized by which table?
- Table 250.122, by the rating of the overcurrent device protecting the circuit.
- EGC for a 15 A circuit (copper)?
- 14 AWG copper.
- EGC for a 20 A circuit (copper)?
- 12 AWG copper.
- EGC for a 60 A circuit (copper)?
- 10 AWG copper.
- EGC for a 100 A circuit (copper)?
- 8 AWG copper.
- EGC for a 200 A circuit (copper)?
- 6 AWG copper.
- What recognizes an acceptable EGC type?
- 250.118 — a copper conductor (insulated or bare), rigid/intermediate metal conduit, EMT, the metal of a listed cable, etc.
- Main bonding jumper?
- The connection at the service that bonds the grounded (neutral) conductor to the equipment ground and enclosure.
- System bonding jumper?
- The equivalent of the main bonding jumper for a separately derived system (e.g., a transformer secondary).
- Main / system bonding jumper sized by?
- The grounding-electrode-conductor table (Table 250.102 / 250.66), based on the supply conductors.
- Separately derived system?
- A system whose power comes from a source (transformer, generator) with no direct electrical connection to the supply conductors.
- Grounded conductor vs grounding conductor?
- Grounded conductor = the neutral (intentionally tied to ground, carries current). Grounding conductor (EGC) = the fault path, carries no current normally.
- Where do grounding and bonding meet?
- At the service, via the main bonding jumper — neutral and equipment ground are bonded there (and only there).
- May a 6 AWG GEC be run without a raceway?
- Yes, if it's free from physical damage and securely fastened to the surface (6 AWG copper or larger).
- Why are neutral and ground bonded only at the service?
- To avoid parallel neutral paths on the equipment ground downstream; subpanels keep neutral and ground separate.
- Purpose of grounding the system to earth?
- Stabilizes voltage to ground and dissipates lightning/surge energy. It does not clear faults.
- Grounded service conductor minimum size?
- At least the value from the GEC table for the service conductors, since it also serves as the effective ground-fault return path.
- Metal water pipe as an electrode — requirement?
- A metal underground water pipe in contact with earth 10+ ft must be used as an electrode and supplemented by an additional electrode.
- Ground-rod length and depth?
- At least 8 ft long, driven so its full length is in contact with the soil (top flush or below grade).
- Two ground rods — when required?
- A single rod with 25 ohms or more resistance to earth must be supplemented by a second electrode (commonly two rods are just installed).
- Service disconnect requirement?
- Must be readily accessible, marked, and able to disconnect all ungrounded service conductors (grouped, limited number).
- What is a feeder?
- Conductors between the service equipment and the final branch-circuit overcurrent device (Article 215).
- What is a branch circuit?
- The conductors between the final overcurrent device and the outlets it serves (Article 210).
- Feeder ampacity (continuous + noncontinuous)?
- At least the noncontinuous load + 125% of the continuous load (before adjustment factors).
- What is a continuous load?
- A load expected to operate for 3 hours or more. Sized at 125% for conductors and overcurrent devices.
- Why size continuous loads at 125%?
- It's the inverse of 80% — it keeps a breaker from running continuously at its full rating, which would overheat it.
- Is fixed electric space heating continuous?
- Yes — treated as a continuous load, so it gets the 125% factor.
- Dwelling general lighting load?
- 3 volt-amperes per square foot of habitable floor area (Article 220).
- Small-appliance and laundry circuits in a load calc?
- Add two small-appliance circuits and one laundry circuit at 1,500 VA each before applying demand factors.
- Dwelling general-lighting demand factors?
- First 3,000 VA at 100%, 3,001–120,000 VA at 35%, remainder at 25% (Table 220.45 in 2023 NEC; 220.42 in 2017/2020).
- Why apply demand factors?
- Loads rarely all run at full load at once; demand factors keep the service from being oversized.
- Clothes-dryer demand factor?
- Table 220.54 lets a feeder serving four or more dryers be reduced, because they don't all run at full load together.
- Electric range demand?
- Table 220.55 provides demand loads for household cooking equipment over 1¾ kW (e.g., one 12 kW range = 8 kW demand).
- Feeder to subpanels — ampacity?
- Must be at least the total calculated load of everything downstream.
- Do demand factors vary by occupancy?
- Yes (Table 220.42/220.45) — e.g., warehouses get a lighting demand factor that offices don't, by expected diversity of use.
- General lighting load for a 1,500 sq ft dwelling (before demand)?
- 1,500 × 3 VA = 4,500 VA.
- Standard vs optional dwelling calculation?
- Standard method (220 Part III) sums loads with demand factors; the optional method (220.82) uses a simpler 100%/40% formula.
- Feeder vs service?
- Service = utility to the building (Article 230). Feeder = service equipment to a downstream panel/overcurrent device (Article 215).
- Continuous-load example?
- Store/office lighting on for the business day, electric heat — anything running 3+ hours.
- Neutral (grounded) feeder conductor load?
- Sized for the maximum unbalanced load (220.61) — the most line-to-neutral load on any one ungrounded conductor.
- What does a 200 A feeder to a 100 A and 60 A subpanel need?
- Ampacity for the combined calculated load of both subpanels (after their own demand factors), not just their breaker sizes.
- What is ampacity?
- The maximum current a conductor can carry continuously without exceeding its temperature rating (Table 310.16).
- 75°C copper ampacity: 12 AWG?
- 25 A — but the small-conductor rule caps its breaker at 20 A.
- 75°C copper ampacity: 10 AWG?
- 35 A — but the small-conductor rule caps its breaker at 30 A.
- 75°C copper ampacity: 8 AWG?
- 50 A.
- 75°C copper ampacity: 6 AWG?
- 65 A.
- 75°C copper ampacity: 4 AWG?
- 85 A.
- 75°C copper ampacity: 3 AWG?
- 100 A.
- 75°C copper ampacity: 1/0 AWG?
- 150 A.
- 75°C copper ampacity: 2/0 AWG?
- 175 A.
- 75°C copper ampacity: 4/0 AWG?
- 230 A.
- Ampacity adjustment for more than 3 conductors?
- Bundling more than three current-carrying conductors in a raceway derates the ampacity (310.15).
- Ampacity adjustment for high ambient temperature?
- Apply the temperature correction factors of Table 310.15(B)(1) — hotter ambient lowers usable ampacity.
- What is AWG?
- American Wire Gauge — the conductor sizing system. A SMALLER number means a LARGER conductor.
- What is kcmil?
- Thousands of circular mils — the size unit for conductors larger than 4/0 AWG (e.g., 250 kcmil).
- EMT — what article?
- Article 358 (electrical metallic tubing).
- EMT support spacing?
- Secured within 3 ft of each box/termination, then supported at least every 10 ft.
- EMT — bends between pull points?
- No more than 360° total (four quarter-bends) between pull points.
- Why limit EMT bends to 360°?
- To keep conductor pulling tension low so insulation isn't damaged during the pull.
- EMT cut ends?
- Must be reamed to remove burrs and rough edges that could damage conductor insulation (358.28).
- Is EMT allowed in severe physical damage areas?
- No — EMT is not permitted where subject to severe physical damage (358.12). Use rigid metal conduit.
- Type NM cable — what article?
- Article 334 (nonmetallic-sheathed cable, 'Romex').
- Where is Type NM cable permitted?
- Dry locations and dwellings/normally dry structures. Not in wet locations or where exposed to damage.
- Type NM cable securing?
- Secured within 12 in of every box and at least every 4.5 ft along the run.
- Type NM in an unfinished basement (small cable)?
- Cables smaller than two 6 AWG or three 8 AWG run through bored holes in joists or on a running board (334.15(C)).
- Rigid metal conduit (RMC) — article?
- Article 344. Heavy-wall, threaded steel; permitted in nearly all locations, including severe physical damage.
- Article 300 covers?
- General requirements for all wiring methods — protecting from physical damage, securing/supporting conductors, raceway rules.
- Conduit fill — one conductor?
- 53% maximum (Chapter 9, Table 1).
- Conduit fill — two conductors?
- 31% maximum — the most restrictive, because a tight pair can jam during the pull.
- Conduit fill — three or more conductors?
- 40% maximum (Chapter 9, Table 1).
- Why do 2 conductors get LESS fill than 3+?
- A snug pair tends to jam against the raceway wall during a pull, so the limit is lower (31% vs 40%).
- Box-fill volume allowance: 14 AWG?
- 2.00 cubic inches (Table 314.16(B)).
- Box-fill volume allowance: 12 AWG?
- 2.25 cubic inches.
- Box-fill volume allowance: 10 AWG?
- 2.50 cubic inches.
- Box-fill volume allowance: 8 AWG?
- 3.00 cubic inches.
- Box-fill volume allowance: 6 AWG?
- 5.00 cubic inches.
- Box fill — how are grounding conductors counted?
- All equipment grounding conductors together count as ONE, based on the largest one present.
- Box fill — how are cable clamps counted?
- All internal cable clamps together count as ONE, based on the largest conductor in the box.
- Box fill — how is a device (switch/receptacle) counted?
- Each yoke/strap counts as TWO, based on the largest conductor connected to that device.
- Box fill — how is a support fitting counted?
- Each fixture stud or hickey counts as ONE, based on the largest conductor in the box.
- Box fill for five 12 AWG + one receptacle (all grounds = 1)?
- 5 (conductors) + 2 (yoke) + 1 (grounds) = 8 units × 2.25 in³ = 18.0 in³ minimum.
- Direct-burial cover — general (Table 300.5)?
- 24 inches for direct-buried cables/conductors rated 0–600 V in the general location.
- Cover for rigid metal conduit (Table 300.5)?
- 6 inches minimum for RMC/IMC.
- Cover under a residential driveway (1- & 2-family)?
- 18 inches for direct-buried UF cable/conductors.
- Cover for a residential 120 V, 20 A GFCI circuit?
- 12 inches (the reduced-cover column of Table 300.5).
- Warning ribbon over buried conductors?
- Table 300.5 generally requires a warning ribbon placed in the trench above buried conductors at the listed depth.
- EGC types recognized by 250.118?
- Insulated/bare copper, RMC, IMC, EMT, the metal sheath of certain cables, and listed flexible conduits under conditions.
- When conductors are upsized for voltage drop, the EGC?
- Must be increased proportionally (250.122(B)) so the fault path keeps pace.
- All conductors of a circuit in a metal raceway?
- Must be in the SAME raceway/cable to avoid inductive heating (the magnetic fields must cancel).
- Conductor insulation rating — what does THHN mean?
- Thermoplastic, High heat-resistant, Nylon-coated — a common 90°C dry-location building wire.
- Why ream a cut raceway?
- Burrs left on the inside of a cut raceway can slice conductor insulation when wires are pulled.
- Which conduit for an area subject to severe physical damage?
- Rigid metal conduit (RMC) — not EMT.
- What does 'circular mil' measure?
- Conductor cross-sectional area — the area of a circle 1 mil (0.001 in) in diameter; more circular mils = larger wire.
- Equipment grounding conductor — does it carry current normally?
- No — it carries current only during a ground fault. The neutral (grounded conductor) carries normal current.
- What is a raceway?
- An enclosed channel (conduit, tubing, wireway) designed expressly to hold conductors.
- What is an overcurrent device?
- A fuse or circuit breaker that opens the circuit when current would overheat the conductor (Article 240).
- What does an overcurrent device protect?
- The CONDUCTOR (and equipment) from excessive current/heat — not the load.
- Overcurrent device location — readily accessible?
- Handle no more than 6 ft 7 in above the floor or platform (240.24); not over steps, in bathrooms, or in clothes closets.
- Small-conductor rule (240.4(D)) — 14 AWG copper?
- Maximum 15 A overcurrent device, regardless of the higher ampacity-table value.
- Small-conductor rule — 12 AWG copper?
- Maximum 20 A overcurrent device.
- Small-conductor rule — 10 AWG copper?
- Maximum 30 A overcurrent device.
- 30 A breaker on 12 AWG — violation?
- Yes. 240.4(D) caps 12 AWG copper at 20 A even if the 90°C ampacity is higher.
- What is a tap conductor?
- A conductor with overcurrent protection ahead of it larger than its ampacity normally allows; permitted under the tap rules.
- 10-foot tap rule (240.21(B)(1))?
- Tap ≤10 ft must have ampacity ≥ the computed load and ≥ the rating of the device it supplies.
- 25-foot tap rule (240.21(B)(2))?
- Tap ≤25 ft must have ampacity ≥ one-third the rating of the overcurrent device protecting the feeder.
- GFCI — what does it protect?
- PEOPLE — it protects against electric shock by sensing current leaking to ground.
- GFCI trip threshold?
- A small ground-fault current imbalance of about 4–6 milliamperes (mA).
- How does a GFCI work?
- It compares current out (hot) to current back (neutral); any imbalance means leakage to ground, so it trips in milliseconds.
- GFCI code section?
- 210.8 (dwelling-unit and other GFCI requirements).
- Where are GFCI receptacles required (dwellings)?
- Kitchens (countertops), bathrooms, garages, unfinished basements, outdoors, laundry areas, and near sinks.
- AFCI — what does it protect?
- PROPERTY — it protects against fire by detecting dangerous arcing faults.
- AFCI code section?
- 210.12 (arc-fault circuit-interrupter protection).
- Where is AFCI protection required?
- Most 120 V, 15- and 20-A branch circuits in dwelling living areas — bedrooms, living rooms, dens, hallways, etc.
- GFCI vs AFCI memory hook?
- GFCI guards against the shock to a person near Ground/water; AFCI guards against the Arc that starts a fire.
- Does extending a circuit trigger AFCI?
- Yes — extending/modifying a branch circuit in an AFCI-required dwelling area generally requires AFCI protection (210.12).
- Replacing a receptacle where GFCI is now required?
- The replacement must be provided with GFCI protection (210.8 applies to replacements in those locations).
- Receptacle spacing — the 6-foot rule (210.52)?
- No point along a wall line is more than 6 ft from a receptacle, so receptacles are ≤12 ft apart.
- Which wall needs a receptacle (210.52)?
- Any wall space 2 ft or wider (measured along the floor line, around corners, not crossing doorways).
- Kitchen countertop receptacle spacing?
- No point along the counter wall line is more than 24 in from a receptacle (210.52(C)).
- Which kitchen counter needs a receptacle?
- Any counter 12 in or wider.
- Working space depth (≤150 V to ground, Condition 1)?
- 3 feet (36 in) of clear depth in front of the equipment (110.26).
- Working space width (110.26)?
- 30 inches, or the width of the equipment, whichever is greater.
- Working space headroom (110.26)?
- At least 6½ feet (78 in) of clear headroom.
- Equipment-door swing requirement (110.26)?
- Doors/hinged panels must open at least 90 degrees.
- Can the working space be used for storage?
- No — it must be kept clear at all times.
- Working-space depth Conditions 2 and 3?
- Increases to 3½ ft (Condition 2) and 4 ft (Condition 3) when grounded or live parts face the working space (≤150 V).
- Core electrical-safety rule?
- Treat every conductor and part as energized until it is tested and proven de-energized.
- What is lockout/tagout?
- OSHA 1910.147 procedure: de-energize, lock the disconnect off, tag it, and verify dead with a meter before servicing.
- Who enforces job-site electrical safety?
- OSHA (e.g., 1910 General Industry, 1926 Construction); the NEC governs the installation itself.
- What is the purpose of PPE for electrical work?
- To protect against shock, arc flash, and burns — insulated gloves/tools, arc-rated clothing, eye and face protection.
- What is arc flash?
- An explosive release of energy from an electrical fault arc, producing intense heat, light, and pressure — a major hazard.
- Continuous-load breaker rule?
- A breaker/conductor serving a continuous load must be sized at 125% of that load (210.20, 215.3).
- Series vs parallel overcurrent coordination?
- The branch breaker must protect the smallest conductor; the feeder OCPD protects the feeder, coordinated so faults clear at the right level.
- What does a GFCI NOT replace?
- The branch-circuit breaker. The breaker protects the wire from overload; the GFCI protects people from shock — different jobs.
- Does a GFCI need an equipment grounding conductor to work?
- No — it senses leakage to ground regardless, so it can protect even on a circuit without an EGC.
- Bathroom branch-circuit requirement?
- A 20 A circuit dedicated to bathroom receptacles (210.11), and those receptacles must be GFCI-protected.
- Kitchen small-appliance circuits?
- At least two 20 A small-appliance branch circuits for countertop receptacles (210.11/210.52(B)).
- What is a dedicated/individual branch circuit?
- A branch circuit that supplies only one piece of utilization equipment (e.g., a dishwasher or a fixed motor).
- Why not over a sink or bathtub for a panel?
- Panels/overcurrent devices can't be in bathrooms or over steps; readiness, dryness, and access are the concerns (240.24).
- Minimum number of 15/20 A general-purpose circuits?
- Enough to serve the computed general lighting load (3 VA/ft²) at the circuit rating (210.11(A)).
- What is selective coordination?
- Designing overcurrent protection so only the device nearest a fault opens, leaving the rest of the system energized.
- Power in a 1,200 W load at 120 V?
- I = P ÷ E = 1,200 ÷ 120 = 10 amperes.
- Resistance of a 240 V, 12 A heater?
- R = E ÷ I = 240 ÷ 12 = 20 ohms.
- Three-phase 480 V, 50,000 W at unity PF — current?
- I = P ÷ (1.732 × E) = 50,000 ÷ (1.732 × 480) ≈ 60 amperes.
- Why does halving voltage (fixed R) halve current?
- By Ohm's law I = E ÷ R, current is directly proportional to voltage when resistance is constant.
- What is a busbar?
- A solid conductor (bar) in a panel that distributes power to the breakers; the neutral and ground each have their own bus.
- Subpanel neutral and ground — bonded?
- No — at a subpanel the neutral (grounded) bus is isolated from the ground (bonding) bus; they bond ONLY at the service.
- What is a bonding jumper?
- A reliable conductor ensuring electrical continuity between metal parts that must be bonded (e.g., around a concentric knockout).
- Grounding electrode system — bonding together?
- All present electrodes (water pipe, rods, Ufer, etc.) must be bonded together to form one grounding electrode system (250.50).
- Effective ground-fault current path?
- An intentionally constructed, low-impedance path that carries fault current back to the source so the OCPD operates (250.4).
- Motor branch-circuit conductor sizing?
- A single continuous-duty motor's branch-circuit conductors are sized at 125% of the motor full-load current (430.22).
- Motor full-load current — from where?
- The NEC motor tables (e.g., Table 430.248/430.250), NOT the nameplate, for branch-circuit and feeder sizing.
- Motor overload protection vs short-circuit protection?
- Overloads (heaters/relays) protect the motor from running overcurrent; the branch-circuit breaker/fuse protects against short circuits and ground faults.
- Feeder for several motors?
- Sized at 125% of the largest motor's FLC plus the sum of the other motors' FLCs (430.24).
- What is demand load vs connected load?
- Connected load = everything added up; demand load = connected load after applying NEC demand factors for realistic simultaneous use.
- MC cable vs NM cable?
- MC (Article 330) has a metal interlocking armor and is allowed in more locations; NM (Article 334) has a nonmetallic sheath, mainly for dry dwellings.
- What is a conduit body (LB, T, C)?
- A fitting that provides access for pulling/splicing conductors at a bend or junction in a raceway run.
- Flexible metal conduit (FMC) — use?
- Article 348 — for connections to equipment subject to movement/vibration (e.g., motors); length and EGC limits apply.
- Liquidtight flexible conduit — where?
- Article 350 (LFMC) — flexible connections in wet/damp/oily locations, such as outdoor motor connections.
- Wet-location wiring methods?
- Use raceways/cables/conductors listed for wet locations (e.g., RMC, PVC, THWN conductors); NM cable is not allowed in wet locations.
- What is PVC conduit (RNC)?
- Rigid nonmetallic conduit (Article 352) — corrosion-resistant; common for underground and wet locations; needs expansion fittings for movement.
- Color code for the grounded (neutral) conductor?
- White or gray. The EGC is green, green/yellow, or bare. Ungrounded (hot) conductors are any other color.
- Why derate when bundling conductors?
- Heat from each conductor can't dissipate as easily when crowded, so the allowable ampacity is reduced (310.15).
- What is a junction box?
- An enclosure where conductors are spliced or pulled; must remain accessible and meet box-fill and pull-box sizing rules.
- Pull-box sizing for a straight pull (4 AWG+)?
- Length at least 8 times the largest raceway's trade size (314.28).
- Pull-box sizing for an angle/U pull (4 AWG+)?
- Distance from the raceway entry to the opposite wall at least 6 times the largest raceway's trade size (314.28).
- GFCI vs AFCI — which goes in a bedroom?
- AFCI (arc-fault) — bedrooms are dwelling living areas. GFCI (ground-fault) goes in wet/grounded areas.
- Dual-function (DF) device?
- A device that provides BOTH GFCI and AFCI protection in one — useful where both are required (e.g., a kitchen).
- Tamper-resistant receptacles — where?
- Required in dwelling units for 125 V, 15- and 20-A receptacles (406.12) to prevent children inserting objects.
- What is an outlet (NEC definition)?
- A point on the wiring system where current is taken to supply utilization equipment — not just a receptacle.
- Why must the OCPD match the conductor, not the load?
- The breaker's job is to open before the conductor overheats; a breaker too large for the wire defeats that protection.
