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Essential Electrical Formulas for HVAC and Electrical Work
Having a solid grasp of key electrical formulas is crucial for troubleshooting and system design. Below are the most commonly used formulas, along with explanations for their practical use.
Ohm's Law
Ohm's Law defines the relationship between voltage (V), current (I), and resistance (R):
V = I × R
I = V / R
R = V / I
Use these formulas to calculate voltage drops, determine proper wire sizing, or troubleshoot circuit issues.
Power Formulas
Power calculations are essential for determining electrical load and system performance:
P = V × I
P = I² × R
P = V² / R
Where:
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P = Power (watts)
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V = Voltage (volts)
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I = Current (amperes)
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R = Resistance (ohms)
These formulas help size transformers, determine heater capacities, and calculate circuit loads.
Electrical Energy Formula
To calculate the total energy consumption of a device:
E = P × t
Where:
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E = Energy (watt-hours)
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P = Power (watts)
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t = Time (hours)
This is useful for calculating power costs and efficiency.
Voltage Drop Formula
For determining voltage loss across a wire:
Voltage Drop (VD) = (2 × K × I × D) / CM
Where:
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K = Resistance constant (copper = 12.9; aluminum = 21.2)
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I = Current (amperes)
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D = Distance (feet)
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CM = Circular mil area of the wire
This helps ensure proper wire sizing to minimize voltage loss.
Capacitor Formulas
For calculating capacitance in circuits:
Q = C × V
Where:
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Q = Charge (coulombs)
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C = Capacitance (farads)
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V = Voltage (volts)
Capacitor sizing is crucial for motor starting circuits and power factor correction.
Three-Phase Power Formula
For calculating power in three-phase systems:
P = √3 × V × I × PF
Where:
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P = Power (watts)
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V = Line voltage
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I = Line current
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PF = Power factor
This formula is commonly used in industrial HVAC and motor control systems.
Resistive Heating (Heat Energy) Formula
For calculating the heat output of an electrical system:
Q = I² × R × t
Where:
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Q = Heat energy (joules)
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I = Current (amperes)
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R = Resistance (ohms)
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t = Time (seconds)
This formula is key when calculating heating elements or electric resistance heating systems.
Voltage imbalance Calculations For 3 Phase equipment
1. Get your average voltage between L1,L2,L3.
2. Now add L1,L2,L3 together and divide by 3. This will get you the average Voltage (AV)
3. Now you need to determine which leg is farthest from the AV.
L1 - AV = X1
L2 - AV = X2
L3 - AV = X3
Which ever X1, X2 ,X3 is the largest, that will be your highest imbalance
4. Now use this formula to get your percentage of imbalance.
% of imbalance = highest imbalance / AV
With this, if your voltage imbalance is 3% or or more, then an electrician will have to be called out to the site and fix it.
