ElectriCalc — Electrician's Field Calculator (NEC)

Ohm's Law / Power Wheel

Enter any two values, get the other two. Leave blanks for what you want solved.

Voltage (V)

Current (A)

Resistance (Ω)

Power (W)

V = I × R P = V × I I = V / R P = I² × R P = V² / R

Single-Phase Power

Voltage (V)

Power factor (0–1)

Power (kW)

I = (kW × 1000) / (V × PF) kVA = (V × I) / 1000

Three-Phase Power

Line voltage (V)

Power factor (0–1)

Power (kW)

I = (kW × 1000) / (√3 × V × PF) kVA = (√3 × V × I) / 1000

Series / Parallel Resistance

Series: Rt = R1 + R2 + … Parallel: 1/Rt = 1/R1 + 1/R2 + …

Ampacity Lookup310.16

Conductor size (AWG / kcmil)

Material

Insulation temp rating

Ambient temperature

Current-carrying conductors in raceway

Base ampacities per NEC Table 310.16. Temperature correction per 310.15(B)(1); adjustment for >3 conductors per 310.15(C)(1). The 60°C column applies to terminations on most equipment ≤100 A unless rated otherwise [110.14(C)].

Wire Size Selector310.16

Required load current (A)

Material

Termination / column

Returns the smallest conductor whose base ampacity ≥ required current. Apply derating/correction separately for fill or high ambient.

Conduit FillCh.9 T1,4,5

Conduit type

Trade size

Conductor type

Allowable fill: 1 wire = 53%, 2 wires = 31%, 3+ wires = 40% [Ch.9 Table 1]. Conductor areas per Ch.9 Table 5; conduit areas per Table 4.

Equipment Grounding Conductor250.122

OCPD rating protecting circuit (A)

EGC material

Minimum equipment grounding conductor per NEC Table 250.122. If ungrounded conductors are upsized for voltage drop, the EGC must be increased proportionally [250.122(B)].

Dwelling Load Calculation (Standard)Art. 220

Living area (sq ft, excl. garage/porch)

Small-appliance branch circuits (≥2)

Laundry branch circuits (≥1)

Fixed appliances nameplate total (VA) — water heater, disposal, dishwasher, etc.

# of fixed appliances (for 75% demand if ≥4)

Electric range nameplate (VA, 0 if none)

Electric dryer nameplate (VA, min 5000)

A/C or heat — larger of the two (VA)

Service voltage

Standard calc per Art. 220 Part III. General lighting 3 VA/ft². First 3000 VA @100%, remainder @35% (general + small-appliance + laundry). Range demand per Table 220.55, dryer per 220.54 (min 5000 VA). HVAC at 100%, larger of heat/cool [220.60]. This is a planning estimate — verify all demand factors.

Box Fill314.16

Largest conductor in box (AWG)

Current-carrying conductors (incl. pigtails entering)

All-same-size grounding conductors (count as 1)

Internal cable clamps present?

Devices (switches/receptacles) — each = 2 volumes

Support fittings / studs (each = 1 volume)

Per 314.16(B): each conductor counts as its size's volume (Table 314.16(B)); device = 2× largest conductor; clamps/support = 1× largest; all grounds = 1× largest.

Motor Full-Load CurrentT.430.250

Horsepower

Voltage (3-phase)

Three-phase induction motor FLC per NEC Table 430.250. Use table values (not nameplate) for sizing conductors and overload per 430.6(A)(1).

Voltage Drop

System voltage (V)

Load current (A)

One-way length (ft)

Conductor

Material

Acceptable drop limit

1Φ: VD = 2 × K × I × L / cmil 3Φ: VD = 1.732 × K × I × L / cmil K ≈ 12.9 (Cu), 21.2 (Al) Ω·cmil/ft

OCPD / Breaker Sizing240.6

Load type

Load current (A)

Continuous loads: conductor & OCPD sized at 125% [210.20(A), 215.3]. Motor branch protection max % per Table 430.52; round up to next standard size if not exceeding the table max [240.6 standard ratings].

Conductor Derating

Conductor size

Column temp rating

Material

Ambient temperature

Current-carrying conductors

Adjusted = Base(90°C) × Ftemp × Fadjust (then limited by termination column)

Grounding Electrode Conductor250.66

Largest service-entrance ungrounded conductor

Material of service conductor

Per NEC Table 250.66. Note exceptions: GEC to a concrete-encased electrode need not exceed 4 AWG Cu [250.66(B)]; to ground rod(s) need not exceed 6 AWG Cu [250.66(A)].