ND Electrician flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Ohm's Law
- The voltage across a resistive circuit equals current times resistance (E = I × R); rearranged, I = E/R and R = E/I. It applies to DC and to the resistive component of AC circuits.
- Power Formula
- Electrical power in watts equals voltage times current (P = E × I). Substituting Ohm's law gives P = I²R and P = E²/R, useful when only current or voltage and resistance are known.
- Series Circuit
- A circuit with one path for current. Current is the same through every component, voltage drops add to the source voltage, and total resistance is the sum of individual resistances.
- Parallel Circuit
- A circuit with multiple current paths. Voltage is the same across each branch, branch currents add to total current, and total resistance is found from 1/RT = 1/R1 + 1/R2 + ...
- Kirchhoff's Current Law
- At any circuit node, the total current entering equals the total current leaving; the algebraic sum of currents at a junction is zero. This reflects conservation of charge.
- Kirchhoff's Voltage Law
- Around any closed loop, the algebraic sum of voltage rises and drops is zero. The source voltage equals the sum of the voltage drops across the loads in the loop.
- Impedance
- The total opposition to alternating current, combining resistance and reactance: Z = √(R² + X²). It is measured in ohms and determines current for a given AC voltage.
- Power Factor
- The ratio of true power in watts to apparent power in volt-amperes, equal to the cosine of the phase angle between voltage and current. Resistive loads have a power factor of 1.
- Voltage Drop Rule
- NEC 210.19(A) informational note recommends no more than 3% voltage drop on a branch circuit and 5% total for branch plus feeder, for reasonable efficiency of operation.
- Continuous Load
- A load expected to operate at maximum current for three hours or more. Per NEC 210.19(A)(1) and 210.20(A), branch-circuit and overcurrent sizing use 125% of the continuous load.
- Standard Ampere Ratings
- NEC 240.6(A) lists standard overcurrent device ratings, including 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, and 250 amperes.
- Ampacity
- The maximum current a conductor can carry continuously under specified conditions without exceeding its temperature rating. Ampacity depends on conductor size, insulation type, and ambient temperature.
- Terminal Temperature Rating
- NEC 110.14(C) requires conductor ampacity to be based on the lowest temperature rating of connected terminations. Equipment rated 100 A or less typically uses the 60°C column unless marked otherwise.
- Equipment Grounding Conductor
- The conductor that connects exposed non-current-carrying metal parts to the grounding system, providing a low-impedance fault path. It is green, green with yellow stripe, or bare.
- Grounded Conductor
- The intentionally grounded circuit conductor, commonly the neutral, identified by white or gray insulation. It carries normal return current but is not the equipment grounding conductor.
- GFCI Protection
- Ground-fault circuit-interrupter protection detects small current imbalances to ground and trips quickly. NEC 210.8 requires it in dwelling bathrooms, garages, outdoors, kitchens, and other listed areas.
- AFCI Protection
- Arc-fault circuit-interrupter protection detects arcing signatures in branch circuits and de-energizes them. NEC 210.12 requires it for dwelling branch circuits in bedrooms and other listed rooms.
- Box Fill Calculation
- NEC 314.16 assigns volume per conductor, such as 2.00 in³ for 14 AWG, 2.25 in³ for 12 AWG, and 2.50 in³ for 10 AWG. Total box volume must equal or exceed the sum.
- Working Clearance
- NEC 110.26 requires a clear space in front of electrical equipment at least 36 inches deep, 30 inches wide, and 6 feet 6 inches high, with depth increasing at higher voltages.
- Branch Circuit
- The circuit conductors between the final overcurrent device protecting the circuit and the outlet or outlets. Branch-circuit conductors are sized for load and protected against overcurrent.
- Feeder
- All circuit conductors between the service equipment, source of a separately derived system, or other power supply and the final branch-circuit overcurrent device. Feeders supply panelboards, not outlets directly.
- Service Equipment
- The necessary equipment, usually a switchboard or panelboard, connected to the load end of service conductors. It contains the main disconnecting means and service overcurrent protection.
- Overcurrent
- Any current in excess of the rated current of equipment or the ampacity of a conductor, including overloads, short circuits, and ground faults. Overcurrent devices protect conductors from damage.
- Short Circuit
- An unintentional low-resistance connection between two circuit points at different potentials, producing very high current. A short circuit bypasses the normal load and trips overcurrent protection.
- Ground Fault
- An unintentional connection between an energized conductor and ground or grounded equipment. It can energize metal enclosures and is the condition GFCI devices are designed to detect.
- Bonding
- The permanent joining of metallic parts to form an electrically conductive path that ensures electrical continuity and capacity to conduct safely any current likely to be imposed.
- Insulation Resistance
- The resistance of conductor insulation to current leakage, measured in megohms with a megohmmeter. Low readings indicate moisture, contamination, or insulation damage and require correction.
- Voltage Divider
- In a series circuit, the voltage across one resistor equals the source voltage times that resistance divided by total resistance. This follows from common current and Ohm's law.
- Conductor Resistance Formula
- Resistance equals resistivity times length divided by cross-sectional area (R = ρL/A). Doubling conductor length doubles resistance; doubling cross-sectional area halves it.
- Alternating Current
- Current that periodically reverses direction, typically 60 Hz in North America. AC allows voltage transformation and dominates utility power distribution over long distances.
- Inductive Reactance
- Opposition to AC current from inductance, calculated as XL = 2πfL. Reactance rises with frequency and inductance, causing current to lag voltage in an inductive circuit.
- Capacitive Reactance
- Opposition to AC current from capacitance, calculated as XC = 1/(2πfC). Reactance falls as frequency and capacitance rise, causing current to lead voltage in a capacitive circuit.