Q
AFCI (Arc-Fault Circuit Interrupter)
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A
A device that recognizes the electrical signature of arcing and de-energizes the circuit before it starts a fire. Required in most residential dwelling areas.
NEC 210.12
Q
Ampacity
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A
The maximum current, in amperes, a conductor can carry continuously without exceeding its temperature rating.
NEC 310.16-310.21
Q
Ampere (A)
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A
The base SI unit of electric current -- one coulomb of charge passing a point per second.
Q
Arc Flash
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A
A sudden release of electrical energy through the air when a high-voltage gap flashes over. Hazard analysis and PPE requirements are governed by NFPA 70E, not the NEC.
Q
Bonding
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A
Permanently joining metallic parts to form a continuous, low-impedance conductive path that can safely carry fault current. Distinct from grounding.
Q
Branch Circuit
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A
The circuit conductors between the final overcurrent protective device and the outlet(s) it serves.
NEC Art. 100
Q
Multiwire Branch Circuit
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A
A branch circuit with two or more ungrounded conductors that share a voltage between them, plus a grounded (neutral) conductor with equal voltage to each ungrounded conductor.
NEC Art. 100
Q
Conduit Fill
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A
The percentage of a conduit's cross-sectional area that may be occupied by conductors -- 53% for 1 conductor, 31% for 2, 40% for 3 or more.
NEC Ch. 9, Table 1
Q
Continuous Load
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A
A load expected to run at maximum current for 3 hours or more. Conductors and OCPDs must be sized at 125% of it.
NEC 210.19, 215.2
Q
Current Transformer (CT)
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A
An instrument transformer that steps a high current down to a safe, measurable level (typically 5A secondary) for metering or monitoring.
Q
Demand Factor
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A
The ratio of a system's maximum demand to its total connected load -- used in load calculations because not everything runs at once.
Q
Disconnect
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A
A device that disconnects the electrical supply from the equipment it serves.
NEC Art. 230
Q
EGC (Equipment Grounding Conductor)
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A
The conductive path connecting non-current-carrying metal parts of equipment back to the grounded system -- gives fault current a low-impedance way home.
NEC 250.118
Q
EMT (Electrical Metallic Tubing)
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A
Thin-walled steel or aluminum raceway. Not rated for direct burial or concrete encasement without a special listing.
NEC Art. 358
Q
Feeder
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A
All circuit conductors between the service equipment (or a separately derived system) and the final branch-circuit overcurrent device.
NEC Art. 100
Q
GFCI (Ground-Fault Circuit Interrupter)
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A
De-energizes a circuit when current to ground exceeds about 5mA. Required in bathrooms, kitchens, garages, outdoors, and other damp/wet locations.
NEC 210.8
Q
GEC (Grounding Electrode Conductor)
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A
The conductor connecting the grounded system conductor (or equipment) to a grounding electrode or the grounding electrode system.
NEC Art. 100
Q
IMC (Intermediate Metal Conduit)
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A
Steel raceway with a wall thickness between EMT and rigid metal conduit. Threadable.
NEC Art. 342
Q
Inverter
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A
Equipment that converts DC power to AC power -- central to PV (solar) systems.
NEC Art. 690, 705
Q
k-Factor
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A
A constant used in voltage-drop math: 12.9 for copper, 21.2 for aluminum. VD = (k x I x L) / CM.
Q
Load Calculation
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A
The process of determining total electrical load on a service or feeder -- Standard method (dwellings) or Optional method.
NEC Art. 220
Q
LB Conduit Body
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A
A conduit body making a 90-degree turn, with the opening on the back ("L") and a removable cover ("B").
Q
Motor Full-Load Current (FLC)
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A
The current value pulled from NEC Tables 430.247-430.252 (not the nameplate) for sizing conductors and short-circuit/ground-fault protection.
NEC 430.247-430.252
Q
Motor FLA (Full-Load Amperes)
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A
The actual current a specific motor draws at rated conditions, per its nameplate -- used to set overload protection.
NEC 430.32
Q
NEC (National Electrical Code)
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A
NFPA 70 -- the standard for safe electrical design, installation, and inspection in the U.S. Revised on a 3-year cycle.
Q
Neutral Conductor
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A
The conductor connected to a system's neutral point that normally carries current -- in 120/240V single-phase, it carries the unbalanced load.
Q
NFPA 70E
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A
The standard for electrical safety in the workplace -- arc flash analysis, safe work practices, and PPE selection.
Q
OCPD (Overcurrent Protective Device)
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A
Any fuse, breaker, or similar device that automatically opens a circuit at a predetermined overcurrent level.
NEC Art. 240
Q
Ohm's Law
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A
The core relationship between voltage, current, and resistance: V = I x R (extended with P = I x V for power).
Q
Power Factor (PF)
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A
The ratio of real power (kW) to apparent power (kVA). A low PF means higher current draw for the same real power.
Q
PVC Conduit
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A
Rigid non-metallic conduit suitable for direct burial and concrete encasement -- needs expansion fittings on long runs.
NEC Art. 352
Q
RMC (Rigid Metal Conduit)
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A
The heaviest-walled steel/aluminum conduit -- threaded, strong physical protection, approved for nearly all locations.
NEC Art. 344
Q
Raceway
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A
An enclosed channel designed to hold wires, cables, or busbars -- includes conduit, wireways, and cable trays.
NEC Art. 100
Q
Separately Derived System
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A
A wiring system whose power source has no direct electrical connection to the supply conductors of another system -- e.g. a transformer or generator.
NEC Art. 100
Q
Service
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A
The conductors and equipment delivering electric energy from the utility to the premises wiring system.
NEC Art. 230
Q
SCCR (Short-Circuit Current Rating)
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A
The maximum short-circuit current equipment can withstand without damage -- must be checked against available fault current on site.
Q
THD (Total Harmonic Distortion)
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A
A measure of waveform distortion from harmonics. High THD from non-linear loads can overheat neutrals and transformers.
Q
Transformer
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A
A static device transferring energy between circuits via electromagnetic induction. V1/V2 = N1/N2 = I2/I1.
Q
VFD (Variable Frequency Drive)
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A
An electronic controller that varies frequency and voltage to adjust AC motor speed -- common in HVAC, pump, and conveyor systems.
Q
Voltage Drop
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A
The loss of voltage between source and load. NEC recommends max 3% on branch circuits, 5% total. VD = (2 x k x I x L) / CM.
NEC 210.19 FPN, 215.2 FPN