DC Electrician flashcards
DC Electrician · Build recall with a focused review session.
31 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Ohm's Law
- The relationship E = I × R, where E is voltage in volts, I is current in amperes, and R is resistance in ohms. Given any two values, the third can be calculated.
- Power Formula
- P = E × I for DC and purely resistive AC circuits. For AC circuits with reactance, true power equals volts times amps times power factor, measured in watts.
- Voltage Drop Formula
- VD = 2 × K × I × L ÷ CM for single-phase circuits, where K equals 12.9 for copper, I is current, L is one-way length in feet, and CM is circular mils.
- Three-Phase Power
- P = 1.732 × E × I × power factor. The 1.732 factor is the square root of three, which arises from the 120-degree phase displacement between the three phases.
- Box Fill Allowance
- Table 314.16(B) assigns volume per conductor: 14 AWG = 2.00 cu in, 12 AWG = 2.25 cu in, 10 AWG = 2.50 cu in. Each device yoke counts as two conductors.
- Continuous Load Rule
- A continuous load is one operating at maximum current for three hours or more. Its calculated load must be multiplied by 125% for branch-circuit and feeder sizing.
- Conductor Derating
- When more than three current-carrying conductors share a raceway, ampacity is reduced per Table 310.15(C)(1): 4 to 6 conductors to 80%, 7 to 9 to 70%.
- Standard OCPD Ratings
- Standard overcurrent device ratings include 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, and 100 amperes, then increasing in 10 A steps to 400 A.
- NM Cable Support
- Nonmetallic-sheathed cable must be secured within 12 inches of every box and at intervals not exceeding 4.5 feet along its run.
- EMT Support
- Electrical metallic tubing must be supported within 3 feet of a box and at intervals not exceeding 10 feet, with additional support where bends or fittings require it.
- Conduit Fill Limits
- Conduit fill is limited by conductor count: one conductor may fill 53% of the cross-sectional area, two conductors 31%, and three or more 40%.
- NM Cable Bend Radius
- Nonmetallic-sheathed cable must be bent to a radius of at least five times the cable diameter, preventing damage to the conductors and sheath.
- Grounding Electrode Rule
- A single rod, pipe, or plate electrode must have a resistance of 25 ohms or less. If it exceeds 25 ohms, a second electrode must be added.
- Box Accessibility
- Junction and outlet boxes must remain accessible without removing permanent building finishes. Boxes may not be buried in walls, ceilings, or floors.
- Receptacle Configurations
- NEMA 5-15R is 15 A/125 V, 5-20R is 20 A/125 V, 6-15R is 15 A/250 V, 14-30R is 30 A/125/250 V, and 14-50R is 50 A/125/250 V.
- GFCI Protection Locations
- GFCI protection is required for 15 A and 20 A receptacles in bathrooms, garages, outdoors, near sinks within 6 feet, and in unfinished basements.
- AFCI Protection
- Arc-fault circuit-interrupter protection is required for 15 A and 20 A branch circuits supplying outlets in dwelling unit bedrooms, living rooms, dining rooms, and similar areas.
- Tamper-Resistant Receptacles
- Tamper-resistant receptacles are required in dwelling units for 15 A and 20 A, 125 V receptacles, with limited exceptions such as dedicated equipment outlets.
- Three-Way Switch
- A three-way switch has three terminals: one common and two travelers. Two three-way switches control a single load from two different locations.
- Service Disconnect
- A service disconnect must be provided at the point where service conductors enter the building and must be marked with its ampere rating and be lockable open.
- Motor Overload Protection
- Motor overload protection is sized from the motor nameplate full-load current. Short-circuit and ground-fault protection follow Article 430, Table 430.52.
- Arc-Flash Risk Assessment
- NFPA 70E requires an arc-flash risk assessment before energized work. Energized work is allowed only where de-energizing adds hazards or is infeasible.
- Limited Approach Boundary
- For a 480 V system, the limited approach boundary is 3 feet 6 inches and the restricted approach boundary is 1 foot. Only qualified persons may cross.
- Lockout/Tagout
- The person performing the work applies the lockout device. The tag must identify that person and the reason for the lockout, and only that person removes it.
- PPE Categories
- Arc-rated PPE categories by incident energy: Category 1 = 4 cal/cm², Category 2 = 8 cal/cm², Category 3 = 25 cal/cm², Category 4 = 40 cal/cm².
- Master Electrician License
- A master electrician license typically authorizes the holder to pull permits, contract for electrical work, and supervise journeyman electricians.
- Change Order
- A change order modifies the scope, price, or schedule of a contract. It must be signed by both parties to be enforceable.
- Surety Bond
- A surety bond is a three-party agreement guaranteeing that the contractor will perform the work or pay damages if the contractor defaults.
- Workers' Compensation
- Workers' compensation insurance covers employee injuries and illnesses arising from employment, regardless of fault, and is required in most states.
- Circuit Breaker Marking
- A circuit breaker must be marked with its ampere rating, voltage rating, and interrupting rating. The interrupting rating must equal or exceed available fault current.
- Recessed Luminaire Clearance
- Recessed luminaires require clearance from thermal insulation unless listed for direct contact. Their junction boxes must remain accessible for service.