Ampacity of a conductor is the maximum current a conductor can carry continuously without exceeding its temperature rating
Apparent Power is power supplied to circuit by the source determined by measuring voltage and current in an inductive or capacitive circuit and then multiplying together
Autotransformer use a single winding for the primary and secondary windings
Branch-Circuit is the circuit section between the last over-current protection device (CB) and receptacles/outlets
Capacitance is the property the stores & releases electrical energy using an electrical field.
Capacitive Reactance is a capacitors opposition to AC current flow, expressed in Ω using Xc
Capacitor permits current to flow by the ability to store and discharge energy as AC current flows in opposite directions
Circular-Mils (cmils) is measurement for cross-sectional area of a conductor. The measurement for stranded wire is the same as solid, and copper is the same as aluminum.
Commutator is a ring around a rotor shaft segmented with insulation between them
Counter-Electromotive Force (a.k.a. back-EMF) is conductor AC induced voltage which opposes current flow
Eddy Currents are in AC circuits as small, independent currents resulting from the expanding and collapsing magnetic field
Efficiency is the total amount of power loss in watts.
Feeder is the circuit section between the off-site power supply and the branch-circuit over-current device. (telephone pole to CB)
Frequency is number of rotor turns per second / cycles per second ÷ Hertz (Hz)
Full-Load Ampere Rating (FLA) is the current drawn by a motor while producing rated horsepower load at its rated voltage, based on rated efficiency and power factor (PF); Motor Nameplate Overload Protection
Full Load Current (FLC) Motor short-circuits and ground faults
High-Leg System is a term used to identify the conductor of a delta-connected system with a voltage rating between 190-208 volts to ground. A.k.a. ‘wild-leg’ and ‘stinger-leg’
Hysteresis Losses is energy lost by (iron core) molecules needing to realign themselves to changing polarity due to AC current expanding/collapsing electromagnetic field
Impedance is the total opposition to electron movement in alternating-current circuits resulting from resistance + inductive reactance + skin effect.
Inductance is an electrical circuit property which stores and releases electrical energy using an electro-magnetic field
Inductive Reactance is the 1 opposition to AC flow; 2 expanding & collapsing magnetic fields within a conductor inducing electromagnetic force opposing AC flow; 3 a self-induced voltage (aka CEMF) acting to oppose the change in conductor current flow; Measured in Ohms, expressed using XL
Integers are whole numbers
Neutral Conductor is the conductor connected to the neutral point of a system that’s intended to carry current under normal conditions
Non-Linear Load is when the current wave form does not follow the voltage wave form
Overcurrent (OC) has 3 factors; Shorts, Grounds, & Overloads; OC is the current in amps greater than the rated current of the equipment or conductors being served resulting in a ╧, short, or OL
Overload is a condition where the current exceeds the equipment amperage rating which can result in equipment damage due to overheating. OL does not protect against ╧ faults nor short circuits but does protect against motor overloads and start failures. Usually nameplate data required for OL protection.
Phase is time or degree between 2 wave forms
Power Factor measures how far the wave forms of current is out-of-phase with voltage. Defined as ratio of True Power (w) to Apparent Power (va). Expressed in Volt-Amps (va)
Power Loss is energy not used for the intended purpose
Root Mean Square (RMS) describes steps (in reverse) to determine effective voltage or current value. RMS is a value 70.7% of the peak positive voltage. Square the voltage at all moments in an AC cycle, take the mean of these, and then take the square root of the mean.
Self-Induced Voltage is voltage induced within conductors by current flow and caused by its own expanding and collapsing magnetic field
Service Factor (SF) indicates how much the motor capacity can be exceeded for short periods without overheating. SF can be considered the motor safety factor. A SF of 1.15 indicates a motor is designed to periodically operate at 115% of rated HP.
Sine waves are AC wave forms
Skin Effect is expanding and collapsing magnetic field induced voltage in AC conductors which repels flowing electrons towards the conductor surface. Greatly impacted by frequency. Stranded wire reduces skin effect.
Temperature Coefficient is the amount of conductor resistance change per temperature degree. + temp-coeff = as temp rises, conductor Ω rises, reducing conductor ampacity.
Three Phase (3Ø) Power Following the voltage, the power derived from an AC source peaks and falls to zero 120 times per second. This causes torque pulsations in motors, creating noise, vibration, and higher shaft stresses. Though minimal in fractional-horsepower household motors, this would be intolerable in larger motors. Three conductors supply AC voltage, offset in time or phase, so that they peak not simultaneously but at equally spaced intervals. This produces constant smooth torque from a motor, because at all moments, the sum of power from all three phases is constant. 3Ø power also eliminates the need for special starting windings required in 1Ø motors.
Transformer is a machine used to transfer electrical energy from one system to another by induction with no physical connection between the 2 systems (except for autotransformers)
True Power (w) is energy consumed and expressed in watts
Turns Ratio is the transformer relationship between the primary to secondary voltage which is equivalent to the relationship between the number of turns of wire on the primary and secondary.
Voltage Drop (VD) is potential loss resulting from current needing to overcome conductor resistance &/or impedance. Calculating requires the conductor resistance and current load. Insignificant differences between uncoated & coated wire. VD is directly proportional to to the conductors Ω and the conductors current magnitude (= amount).
Voltage-Nominal is expected utility source voltage (i.e. 120/240V)
Voltage-Rated is delivered source voltage after voltage drop and losses (i.e. 115/230V)