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# Electrical Formulas

**Mike Holt's Important Electrical Equations Chart PDF 1.4 MB**

Subject | Description | Word™ | Excel™ | |

Arc Blast Calculator | Spreadsheet to calculate Arc Blast in accordance with NFPA 70E | — | Download | — |

Fault Current | Electrical Plan Review: Calculations Answer Sheet | — | — | Download |

Fault Current | Electrical Plan Review: Manual Inside | — | — | Download |

Fault Current | Electrical Plan Review: Cover and Diagram | — | — | Download |

Fault Current | Calculator: Point-to-Point Method by John Sokolik | — | Download | — |

FIPS 94 - Electrical Power for Computer Installations | This is excellent publication (1-23-99) | — | — | Download |

kVar
Calculator [ Link ] |
Manachos Engineering's Calculator for design and construction of electromechanical projects | — | — | — |

Capacitor kVAR Calculator | Spreadsheet to determine capacitor kVAR required to improve power factor (PF). | — | Download | — |

Software [ Link ] | Flashworks - Electrical Service Load Calculations including: Panel Sizing & Balancing, Conductor & Conduit Sizing, Short Circuit Calculation, and Voltage Drop Calculations for both Residential, Commercial and Industrial buildings | — | — | — |

Residential Load Calculations | Dwelling Unit | — | — | — |

Touch Potential 2-Wire Circuit | Open Neutral 2-Wire Circuits | — | Download | — |

Touch Potential 3-Wire Circuit | Open Neutral 3-Wire Circuits | — | Download | — |

Wiring and Raceway Chart | Just view and print! | — | — | Download |

**Conversion Formulas**

Area of Circle = \(\pi r^2\)

Breakeven Dollars = Overhead Cost $/Gross Profit %

Busbar Ampacity AL = 700A Sq. in. and CU = 1000A Sq. in.

Centimeters = Inches x 2.54

Inch = 0.0254 Meters

Inch = 2.54 Centimeters

Inch = 25.4 Millimeters

Kilometer = 0.6213 Miles

Length of Coiled Wire = Diameter of Coil (average) x Number of Coils x \(\pi\)

Lightning Distance in Miles = Seconds between flash and thunder/4.68

Meter = 39.37 Inches

Mile = 5280 ft, 1760 yards, 1609 meters, 1.609 km

Millimeter = 0.03937 Inch

Selling Price = Estimated Cost $/(1 - Gross Profit %)

Speed of Sound (Sea Level) = 1128 fps or 769 mph

Temp C = (Temp F - 32)/1.8

Temp F = (Temp C x 1.8) + 32

Yard = 0.9144 Meters

**Electrical Formulas Based on 60 Hz**

Capacitive Reactance (X_{c}) in Ohms = 1/(2\(\pi\) f C)

Effective (RMS) AC Amperes = Peak Amperes x 0.707

Effective (RMS) AC Volts = Peak Volts x 0.707

Efficiency (percent) = Output/Input x 100

Efficiency = Output/Input

Horsepower = Output Watts/746

Inductive Reactance (X_{L} in Ohms = 2\(\pi\) f L

Input = Output/Efficiency

Neutral Current (Wye) =\(\sqrt{A^2+B^2+C^2-(AB+BC+AC)}\)

Output = Input x Efficiency

Peak AC Volts = Effective (RMS) AC Volts x \(\sqrt 2\)

Peak Amperes = Effective (RMS) Amperes x \(\sqrt 2\)

Power Factor (PF) = Watts/VA

VA (apparent power) = Volts x Ampere or Watts/Power Factor

VA 1-Phase = Volts x Amperes

VA 3-Phase = Volts x Amperes x \(\sqrt 3\)

Watts (real power) Single-Phase = Volts x Amperes x Power Factor

Watts (real power) Three-Phase = Volts x Amperes x Power Factor x \(\sqrt 3\)

**Parallel Circuits**

Note 1: Total resistance is always less than the smallest resistor

Note 1: RT = 1/(1/R1 + 1/R2 + 1/R3 +...)

Note 2: Total current is equal to the sum of the currents of all parallel
resistors

Note 3: Total power is equal to the sum of power of all parallel resistors

Note 4: Voltage is the same across each of the parallel resistors

**Series Circuits**

Note 1: Total resistance is equal to the sum of all the resistors

Note 2: Current in the circuit remains the same through all the resistors

Note 3: Voltage source is equal to the sum of voltage drops of all resistors

Note 4: Power of the circuit is equal to the sum of the power of all resistors

**Transformer Amperes**

Secondary Amperes 1-Phase = VA/Volts

Secondary Amperes 3-Phase = VA/(Volts x \(\sqrt 3\))

Secondary Available Fault 1-Phase = VA/(Volts x %impedance)

Secondary Available Fault 3-Phase = VA/(Volts x \(\sqrt 3\) x %Impedance)

Delta 4-Wire: Line Amperes = Phase (one winding) Amperes x \(\sqrt 3\)

Delta 4-Wire: Line Volts = Phase (one Winding) Volts

Delta 4-Wire: High-Leg Voltage (L-to-G) = Phase (one winding) Volts x 0.5 x \(\sqrt
3\)

Wye: Line Volts = Phase (one winding) Volts x \(\sqrt 3\)

Wye: Line Amperes = Phase (one winding) Amperes

**Voltage Drop**

VD (1-Phase) = 2KID/CM

VD (3-Phase) = \(\sqrt 3\) KID/CM

CM (1-Phase) = 2KID/VD

CM (3-Phase) = \(\sqrt 3\) KID/VD

**Code Rules**

Breaker/Fuse Ratings – 240.6(A)

Conductor Ampacity – 310.15 and Table 310.16

Equipment Grounding Conductor – 250.122

Grounding Electrode Conductor – 250.66

Motor Conductor Size – 430.22 (Single) 430.24 (Multiple)

Motor Short-Circuit Protection – 430.52

Transformer Overcurrent Protection – 450.3

**Constants**

\(\pi\)(Pi) = (3.142 approximately)

\(\sqrt 2\) = 1.414 (approximately)

\(\sqrt 3\) = 1.732 (approximately)

f = Frequency

r = radius

d = diameter

C = Capacitance (farads)

L = Inductance (henrys)

CM = Circular Mils (Chapter 9, Table 8)

VD = Volts Drop

K75^{o}C = (12.9 ohms CU) (21.2 ohms AL)

I = Amperes of load

D = Distance in ft one way