ND Electrician cheat sheet

Ohm's law: E = I × R; power P = E × I = I²R = E²/R. In a series circuit current is common and voltage divides; in a parallel circuit voltage is common and current divides.

Kirchhoff's current law: the algebraic sum of currents at any node is zero (current in equals current out). Kirchhoff's voltage law: the algebraic sum of voltage drops around any closed loop is zero.

Ampacity and voltage drop: NEC 210.19(A) informational note recommends total voltage drop no greater than 3% on a branch circuit and 5% combined branch plus feeder for reasonable efficiency of operation.

Conductor sizing: continuous loads are taken at 125% per NEC 210.19(A)(1) and 210.20(A); the 60°C, 75°C, or 90°C ampacity column used depends on the terminal ratings and the conductor insulation, per NEC 110.14(C).

Overcurrent protection: the standard ampere ratings in NEC 240.6(A) are 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200 A and above.

Grounding and bonding: NEC Article 250 distinguishes the grounded conductor (neutral, white or gray) from the equipment grounding conductor (green, green with yellow stripe, or bare). Receptacle grounding and bonding jumpers must be sized per NEC Table 250.122.

Receptacle and GFCI rules: NEC 210.8 requires GFCI protection for personnel in dwelling bathrooms, garages, outdoors, kitchens, laundry areas, and other listed locations; NEC 210.12 requires AFCI protection for dwelling branch circuits in the listed rooms.

Box fill and working space: NEC 314.16 uses a volume allowance per conductor (e.g., 2.00 in³ for 14 AWG, 2.25 in³ for 12 AWG, 2.50 in³ for 10 AWG); NEC 110.26 requires working clearance of at least 36 in deep, 30 in wide, and 6 ft 6 in high in front of electrical equipment.

Ohm's law applies to resistive loads; for AC circuits impedance Z = √(R² + X²) and the power factor is cos θ, so true power P = E × I × PF. In a purely inductive or capacitive circuit, current and voltage are 90° out of phase.

Ohm's law: E = I × R; power P = E × I = I²R = E²/R. In a series circuit current is common and voltage divides; in a parallel circuit voltage is common and current divides.

Kirchhoff's current law: the algebraic sum of currents at any node is zero (current in equals current out). Kirchhoff's voltage law: the algebraic sum of voltage drops around any closed loop is zero.

Ampacity and voltage drop: NEC 210.19(A) informational note recommends total voltage drop no greater than 3% on a branch circuit and 5% combined branch plus feeder for reasonable efficiency of operation.

Conductor sizing: continuous loads are taken at 125% per NEC 210.19(A)(1) and 210.20(A); the 60°C, 75°C, or 90°C ampacity column used depends on the terminal ratings and the conductor insulation, per NEC 110.14(C).

Overcurrent protection: the standard ampere ratings in NEC 240.6(A) are 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200 A and above.

Grounding and bonding: NEC Article 250 distinguishes the grounded conductor (neutral, white or gray) from the equipment grounding conductor (green, green with yellow stripe, or bare). Receptacle grounding and bonding jumpers must be sized per NEC Table 250.122.

Receptacle and GFCI rules: NEC 210.8 requires GFCI protection for personnel in dwelling bathrooms, garages, outdoors, kitchens, laundry areas, and other listed locations; NEC 210.12 requires AFCI protection for dwelling branch circuits in the listed rooms.

Box fill and working space: NEC 314.16 uses a volume allowance per conductor (e.g., 2.00 in³ for 14 AWG, 2.25 in³ for 12 AWG, 2.50 in³ for 10 AWG); NEC 110.26 requires working clearance of at least 36 in deep, 30 in wide, and 6 ft 6 in high in front of electrical equipment.

Ohm's law applies to resistive loads; for AC circuits impedance Z = √(R² + X²) and the power factor is cos θ, so true power P = E × I × PF. In a purely inductive or capacitive circuit, current and voltage are 90° out of phase.