Electrical Equations (Explanation)

Voltage Drop Calculation #

• Vdrop​ is the voltage drop in volts (V),
• L is the one-way length of the run in feet (ft),
• I is the current in amperes (A),
• R is the resistance of the wire in ohms per thousand feet (Ω/kft).

Ohm’s Law #

Defines the relationship between voltage (V), current (I), and resistance (R) in an electrical circuit.

V=I×R

• Voltage (V) is measured in volts (V).
• Current (I) is measured in amperes (A).
• Resistance (R) is measured in ohms (Ω).

Power Equation #

• P=V×I
  • Power (P) is measured in watts (W).

Relates electrical power (P) with voltage (V) and current (I).

Power in terms of Resistance and Current #

Derived from Ohm’s Law and the Power equation.

• P=I² × R

Power in terms of Voltage and Resistance #

Also derived from Ohm’s Law and the Power equation.

• P=V² x R

Kirchhoff’s Voltage Law (KVL) #

States that the sum of all electrical voltages around any closed network is zero.

• ∑V=0
  • This principle is used to calculate unknown voltages in a circuit loop.

Kirchhoff’s Current Law (KCL) #

States that the total current entering a junction must equal the total current leaving the junction.

• ∑I in = ∑I out

Capacitance and Charge #

Describes the relationship between the charge (Q) stored in a capacitor, its capacitance (C), and the voltage (V) across it.

• Q=C×V
  • Charge (Q) is measured in coulombs (C).
  • Capacitance (C) is measured in farads (F).

Inductive Reactance #

Determines the reactance (X_L) offered by an inductor at a certain frequency (f).

• XL   = 2 π f L
  • XL  is measured in ohms (Ω).
  • Frequency (f) is measured in hertz (Hz).
  • Inductance (L) is measured in henrys (H).