Useful Formulas
Series Circuits - Rules
1. Total resistance is equal to the sum of all the resistors.
2. Current in the circuit remains the same through all the resistors.
3. Voltage source is equal to the sum of voltage drops of all resistors.
4. Power of the circuit is equal to the sum of the power of all resistors.
Parallel Circuits - Rules
1. Total resistance is always less than the smallest resistor.
RT = 1/(1/R1 + 1/R2 + 1/R3 +...)
2. Total current is equal to the sum of the currents of all parallel resistors.
3. Total power is equal to the sum of power of all parallel resistors.
4. Voltage is the same across each of the parallel resistors.
National Electrical Code
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