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Electrical Calculators, Practical Guides & EL Tronic Media

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V = I × R

Ohm's Law Calculator

Calculate Voltage (V), Current (Amps), Resistance (Ω), and Power (Watts) in single-phase circuits.

Voltage (V):120 V
Current (I):10 A
Power (P):1,200 W (1.2 kW)
VD = 2 × K × I × L / CM

Voltage Drop Calculator

Calculates conductor voltage drop percentage according to NEC 3% branch limit standards.

100ft Copper #10:1.98% Drop
NEC Compliance:PASS (< 3%)
P = √3 × V × I × PF

3-Phase Power Calculator

Industrial 480V/208V delta and wye 3-phase real (kW) and apparent (kVA) power calculations.

480V 50A (0.85 PF):35.33 kW
Apparent Power:41.57 kVA
AWG / mm² Ampacity

Cable Size & AWG

Conductor sizing by ampacity, ambient temperature correction factors, and conduit fill.

30A Continuous:#10 AWG Cu
100A Service:#4 AWG Cu / #2 Al
I = (HP × 746) / (V × Eff × PF)

Motor Current (FLA)

Full Load Amps (FLA) for AC single-phase and 3-phase induction motors with locked rotor amps.

10 HP (460V 3Ø):14.0 Amps FLA
Breaker Rec:30A Thermal-Mag
kVA = (V × I × √3) / 1000

Transformer Sizing

Primary and secondary current ratings, turns ratio, and impedance voltage drops.

75 kVA 480V Pri:90.2 Amps
208V Sec:208.2 Amps
1 HP = 0.745699 kW

HP ↔ kW Converter

Exact conversion between electrical horsepower, mechanical horsepower, and metric kilowatts.

50 HP Mechanical:37.28 kW
100 kW Generator:134.10 HP
T = (V × Ah × Eff) / W

Battery Backup Runtime

Calculate inverter runtime, solar battery bank capacity, and Peukert's exponent adjustments.

12V 100Ah @ 200W:5.1 Hours
Usable Energy (80% DOD):960 Wh
kWh = kW × PSH × PR

Solar PV Array Sizing

Photovoltaic daily solar generation, peak sun hours (PSH), array tilt, and inverter sizing.

10 kW System (5.0 PSH):42.5 kWh / day
Annual Output:15,512 kWh
R = (V_s - V_f) / I_f

LED Series Resistor

Determine current-limiting resistance and resistor wattage rating for single or series LEDs.

12V Supply, 3.2V LED:440 Ω (Use 470 Ω)
Resistor Power:0.18W (Use 1/4W)
PF = kW / kVA • Q_c

Power Factor & kVAR

Determine active, apparent, reactive power, and calculate capacitor bank sizing to reach target PF.

50 kW @ 0.72 PF → 0.95:31.8 kVAR Cap
Feeder Current Drop:-24.2% Amps
Cost = kWh × Rate

Electricity Cost & kWh

Calculate daily, monthly, and yearly appliance electric power consumption, kWh usage, and utility cost.

1,500W (8 hrs/day @ $0.15):12 kWh / day
Estimated Utility Cost:$54.00 / month
NEC Ch 9 Table 1

Conduit Fill & Capacity

Calculates maximum allowable THHN conductors inside EMT or PVC conduit to comply with NEC 40% limits.

3/4" EMT + 3x #12 AWG:18.7% Fill (PASS)
Max Wires Allowed:16 Wires Max
NEMA MG-1 %VUB

Voltage Unbalance (NEMA)

Percent voltage unbalance, negative-sequence ratio and motor derating from three line voltages.

480/472/456 V:2.84% unbalance
Motor derating:0.89
η = Pout / Pin

Motor Efficiency & Losses

Shaft output vs electrical input, typical copper, core and mechanical losses and yearly loss cost.

50 HP, 58 A, 0.87 PF:92.8% efficiency
Losses:2.9 kW
MVAsc, kA & peak

3-Phase Fault Level

Symmetrical fault MVA, short-circuit kA and first-cycle peak for a substation bus.

1500 kVA, 250 MVA utility:28.4 kA
Peak (X/R 6):64 kA
NEC 430.122 / MG-1 Pt 31

VFD Cable & Reflected Wave

Inverter-duty motor cable ampacity, carrier heating and reflected-wave peak voltage.

65 A motor, 150 ft:3 AWG Cu
Peak at motor:1,290 V
NEC Table 250.66

Grounding Electrode Conductor

Sizes the GEC from the largest service-entrance conductor, with the rod and concrete-encased electrode caps.

4/0 Cu service:2 AWG Cu GEC
Rod-only cap:6 AWG Cu
NEC Table 250.122

Equipment Grounding Conductor

Finds the minimum equipment grounding conductor from the breaker or fuse rating, including 250.122(B) upsizing.

20 A breaker:12 AWG Cu EGC
100 A breaker:8 AWG Cu EGC
NEC Article 430

Motor Branch Circuit

Motor FLC from Tables 430.248/250, conductors at 125%, breaker or fuse maximum and overload setting.

10 HP, 460 V, 3φ:14 A FLC
Inverse-time breaker:35 A max
NEC 314.16

Box Fill

Counts conductors, devices, clamps and grounds against the volume of an outlet or junction box.

4×1-1/2 sq, 6×14 AWG:18 in³ used
Box capacity:21 in³ (PASS)
NEC 690.8 / VD

DC Solar Cable

Sizes 12 V, 24 V and 48 V solar and battery cable for ampacity and voltage drop.

24 V, 50 A, 15 ft:4 AWG Cu
Voltage drop:1.93%
kW = (Load + Surge) × 1.25

Standby Generator Sizing

Size standby generators for continuous running loads and motor locked-rotor inrush surge.

10 kW + 3 HP Motor Surge:18.1 kW Peak
Recommended Gen:22.6 kW (28.3 kVA)
I_SC = I_FLA / (%Z / 100)

Short Circuit & AIC Rating

Computes maximum symmetrical short circuit fault current (SCCA) at transformer secondary.

100 kVA 480V (4.5%Z):2,673 A SCCA
Breaker Rating:10 kA AIC Min
f_r = 1 / (2π √(LC))

LC Resonant Frequency

Determine resonant frequency and characteristic reactance for LC tank circuits and RF filters.

1 mH + 10 µF Tank:1,591.55 Hz
Impedance at Resonance:10.0 Ω
E = ½ C V² • Q = C V

Capacitor Stored Energy

Calculates stored electrostatic energy in Joules and charge in Coulombs for capacitors.

100 µF @ 400V DC:8.00 Joules
Electric Charge:40.0 mC
V_out = V_in × R₂ / (R₁ + R₂)

Voltage Divider

Calculate output voltage, circuit current, and power dissipation in resistor attenuation pairs.

12V in (10kΩ / 3.3kΩ):2.98 Volts
Circuit Current:0.90 mA
V_G = V_in × [ΔRatio]

Wheatstone Bridge

Compute differential galvanometric output voltage and balance resistance for bridge sensors.

5V in (1kΩ bridge / 1.05kΩ R4):+12.20 mV Offset
Balance Resistance:1,000.0 Ω
kW = BTU / 3412.14

Electric Space Heating

Determine required heating kW capacity and dedicated 240V circuit breaker sizing for rooms.

1,000 cu ft + 30°F Rise:2.98 kW (10,175 BTU)
Breaker Sizing (125%):16 Amp Double-Pole
Bill = Demand + Energy

Tariff & Peak Demand

Calculate commercial utility bills combining 15-minute peak kW demand charges with kWh usage.

45 kW Peak + 12k kWh:$1,522.50 Total
Blended Tariff Rate:$0.127 / kWh
λ = v / f • ¼λ = λ / 4

Frequency & Wavelength

Converts frequency to physical wavelength λ and calculates quarter-wave antenna whip length.

100 MHz FM Radio:λ = 3.00 m
Quarter-Wave Antenna:29.5 inches
τ = R × C

RC Time Constant

Calculate RC charging/discharging time constant τ (63.2% threshold) and 5τ full charge time.

10 kΩ + 100 µF:τ = 1.000 s
5τ Full Charge:5.000 Seconds
τ = L / R

RL Time Constant

Calculate RL circuit time constant τ, magnetic field rise time, and stored energy.

10 mH + 50 Ω:τ = 0.200 ms
5τ Steady State:1.000 ms
dBm = 10 log₁₀(P / 1mW)

Decibel (dBm / dBu / dBV)

Convert RF power in milliwatts to dBm, and AC signal voltages to dBu / dBV levels.

10 mW RF Output:+10.00 dBm
Voltage (50Ω):0.707 Vrms
δ = √(ρ / (π f μ))

AC Skin Effect & Depth

Calculates AC skin depth penetration in copper and aluminum conductors across operating frequencies.

Copper @ 60 Hz:δ = 8.47 mm
Copper @ 1 MHz:δ = 0.066 mm
N_p / N_s = V_p / V_s

Transformer Turns Ratio

Calculate primary to secondary turns ratio, output voltage step-down/up, and current scaling.

240V to 12V Step-Down:Ratio 20:1
Secondary Current:20× Primary Amps
R_Y = R_Δ / 3

Delta-Wye (Δ-Y) Conversion

Convert 3-phase balanced or unbalanced delta resistor networks to equivalent wye configurations.

Balanced 30Ω Delta:10.0 Ω Wye Leg
Power Balance:100% Equivalent
1/R_eq = 1/R₁ + 1/R₂

Series & Parallel Networks

Calculate total equivalent resistance and total equivalent capacitance for series/parallel combinations.

100Ω || 100Ω Parallel:50.0 Ω Total
100Ω + 100Ω Series:200.0 Ω Total
A_v = 1 + (R_f / R_in)

OP-AMP Voltage Gain

Non-inverting and inverting operational amplifier closed-loop voltage gain and output voltage.

Rf=10k, Rin=1k (Non-Inv):Gain A_v = 11.0
Decibel Gain:20.83 dB
X_L = 2π × f × L

Inductive Reactance (X_L)

Calculates AC inductive reactance in ohms and stored magnetic energy in Joules.

10 mH @ 60 Hz:X_L = 3.77 Ω
10 mH @ 1 kHz:X_L = 62.83 Ω
X_C = 1 / (2π f C)

Capacitive Reactance (X_C)

Calculate AC capacitive reactance in ohms for power supply decoupling and AC filtering.

10 µF @ 60 Hz:X_C = 265.26 Ω
10 µF @ 1 kHz:X_C = 15.92 Ω
kW = (3600 × N) / (Kh × T)

Meter Pulse & Instant Load

Calculate real-time power consumption from utility meter disk Kh or optical LED flashes.

10 pulses in 30s (Kh 1.0):1.20 kW Load
Current Draw (230V):5.22 Amps
Ampacity ≈ Area × Density

Copper & Al Busbar Capacity

Determine maximum ampacity rating for solid copper and aluminum electrical busbars.

1/4" × 2" Copper Bar:500 Amps
Aluminum Bar:375 Amps
R_g = (ρ / 2πL) [ln(8L/d)-1]

Ground Rod Resistance

Calculates grounding electrode resistance to earth based on soil resistivity (Ω·m) per IEEE 80.

8ft Rod in 100 Ω·m Soil:27.8 Ω Resistance
NEC 250.53 Rule:25 Ω Target
I = 0.048 × ΔT^0.44 × A^0.725

PCB Trace Width (IPC-2221)

Calculate required printed circuit board copper trace width for target current and temperature rise.

3A @ 10°C Rise (1 oz Cu):52.4 mil (1.33 mm)
2 oz Copper:26.2 mil (0.67 mm)
f = 1.44 / ((R₁ + 2R₂) C)

NE555 Timer Astable

Calculate pulse frequency, period, high/low time, and duty cycle for NE555 timer IC circuits.

R1=1k, R2=10k, C=100nF:f = 685.7 Hz
Duty Cycle:52.4% High
I_N = √(ΣI² - ΣI_a I_b)

3-Phase Unbalanced Neutral

Calculates neutral conductor current flow resulting from unbalanced 3-phase 4-wire loads.

Phase A=100A, B=80A, C=60A:I_N = 34.6 Amps
Balanced Loads:I_N = 0 Amps
P_AC = P_DC × Efficiency %

Solar Inverter Output

Calculate AC output power, DC array clipping loss, and weighted CEC inverter efficiency.

5 kW DC @ 97.5% Eff:4.875 kW AC
Heat Loss:125 Watts
Time = kWh / (kW × Eff)

EV Charging Time

Calculate EV battery charging duration for Level 1 (120V), Level 2 (240V AC), and Level 3 DC Fast Charging.

60 kWh @ 7.2 kW (L2):9.2 Hours
DC Fast Charge 50 kW:1.3 Hours
T = 9550 × kW / rpm

Motor Torque & Power

Shaft torque in N·m and lb·ft from motor power and speed, with efficiency, losses and shaft shear stress.

37 kW @ 1480 rpm:238.8 N·m
Imperial:176.1 lb·ft
S = (Ns − Nr) / Ns

Motor Slip & Speed

Synchronous speed, slip percentage and rotor frequency from supply frequency, poles and rotor speed.

4-pole, 60 Hz, 1750 rpm:2.78% slip
Rotor frequency:1.67 Hz
N = 120 f (1 − S) / P

VFD Frequency & Speed

Shaft rpm, V/Hz voltage and low-speed torque derating for constant- and variable-torque loads.

1750 rpm motor @ 30 Hz:875 rpm
Voltage:230 V (7.67 V/Hz)
LRA = kVA/HP × HP × 1000 / (√3 V)

Motor Inrush & LRA

Starting inrush for direct-on-line, star-delta and soft-starter methods with breaker pickup guidance.

50 HP, 460 V, code G (DOL):395 A
Inrush / FLA:6.07 ×
C = P η / (2π f V²)

Motor Run Capacitor

Run and start capacitor sizing in µF with minimum AC working voltage for single-phase motors.

1 HP @ 230 V 60 Hz:26.2 µF
Rating:370 V AC min
R = V_DC² / P_peak

Brake Resistor Calculator

Dynamic braking resistance in ohms and continuous watt rating from DC bus voltage, regen power and duty.

30 kW peak @ 750 VDC:18.75 Ω
Continuous (10% duty):3.0 kW
P = (C × 2π f V²) / 10⁶

Motor Power from Run Cap

Determine single-phase motor power in Watts, HP, and kW given its run capacitor microfarad (µF) rating.

45 µF @ 230V 50Hz:748 W (1.0 HP)
Formula:Inverse Run Cap
C_start ≈ 3.5 × C_run

Motor Start Capacitor

Calculate starting capacitor rating (µF) for high starting torque CSCR / CSIR single-phase motors.

1 HP @ 230V 50Hz:157 µF (135–180 µF)
Duty Cycle:Short-Duty 250V-330V
P = (C_start × 2π f V²) / (3.5 × 10⁶)

Motor Power from Start Cap

Determine motor power rating in Watts, HP, and kW given its start capacitor microfarad (µF) rating.

160 µF @ 230V 50Hz:760 W (1.02 HP)
Formula:Inverse Start Cap
THD % = √(ΣV_n²) / V₁ × 100

Total Harmonic Distortion (THD)

Calculates total voltage and current harmonic distortion percentage according to IEEE 519 standards.

V1=230V, V3=11.5V, V5=4.6V:THD = 5.38%
IEEE 519 Standard:5% Limit
η = P_out / (P_out + P_loss)

Transformer Efficiency & Loss

Calculate transformer operating efficiency, core losses, copper losses, and peak efficiency load point.

100 kVA @ 75% Load (0.8 PF):98.48% Efficiency
Losses (250W Core / 1.2kW Cu):925 W Total
kVA_VV = √3 × kVA_1φ

Open-Delta (V-V) Capacity

Determine continuous 3-phase capacity using two single-phase transformers in emergency open-delta.

2 × 50 kVA Transformers:86.6 kVA 3-Phase
Bank Capacity Ratio:57.7% of Full Delta
IEEE Std 80 Earth Grid

Substation Earthing Grid

Calculate substation grounding grid resistance based on soil resistivity, grid area, and conductor length.

100 Ω·m, 500 m² Grid Area:R_g = 2.31 Ω
IEEE 80 Target:< 1.0 Ω Recommended
S = √(I² × t) / k

Cable Fault Withstand Size

Calculate minimum conductor cross-section (mm²) to withstand fault current thermal stress per IEC 60364-5-54.

10 kA Fault @ 0.1 sec (Cu/XLPE):22.1 mm² (Rec 25mm²)
Standard Compliance:IEC 60364 Adiabatic
NEMA Code Letter Inrush

Motor Locked Rotor Amps

Calculate motor starting inrush current (LRA) using NEMA code letter kVA/HP classifications.

10 HP @ 460V 3-Phase (Code G):LRA = 74.1 Amps
Inrush kVA:59 kVA Starting
t_accel = J ΔN / (9.55 T)

Star-Delta Transition Timer

Calculate motor run-up acceleration time and recommended Star to Delta switching timer delay.

J = 2.5 kg·m², 1450 RPM, 80 N·m:4.74 Sec Acceleration
Timer Delay:Set 5.2 Seconds
NEC 430.32 Pickup

Thermal Overload Relay

Calculate motor thermal overload relay setting and trip class timing according to NEC standards.

25A FLA, 1.15 Service Factor:Set 31.25 Amps
Trip Class 10:≤ 10s @ 600% FLA
N_s = 120 f / P

VFD Motor Speed & Slip

Calculate synchronous speed, actual rotor RPM, and slip percentage across variable VFD operating frequencies.

4 Poles @ 50 Hz (1440 RPM):N_s = 1500 RPM
Rotor Slip:4.0% (60 RPM Slip)
NEC 690.7 Temp Voc

Solar String Cold Voc

Calculate maximum expected cold open-circuit voltage for solar strings at lowest ambient site temperature.

450V STC Voc @ -10°C (-0.28%/°C):Max Voc = 494.1 V
Inverter Sizing:< 500V Max Input
MPPT vs PWM Sizing

Solar Charge Controller

Calculate required charge controller ampacity and determine optimal MPPT or PWM technology selection.

1200W Array @ 24V Bank:Req 62.5 Amps
Recommended Controller:80A MPPT Unit
Peukert's Law Runtime

Battery Peukert Capacity

Calculate actual battery runtime and effective usable capacity under continuous high-discharge current loads.

100Ah @ 20Hr (15A Load, k=1.15):5.65 Hours Runtime
Effective Capacity:84.8 Usable Ah
NEC 625 125% Rule

EV Charger Circuit Sizing

Calculate breaker size and minimum conductor gauge for Level 2 EV charging stations per NEC Article 625.

7.2 kW Charger @ 240V AC:30A Load / 37.5A Req
Breaker & Wire:40A 2P (8 AWG Cu)
IEC 61643-11 SPD

Surge Protection Device (SPD)

Calculate continuous operating voltage (Uc) and surge discharge capacity (In/Imax) for distribution panels.

230V TN-S System (Type 2):U_c ≥ 265V AC
Discharge Capacity:In=20kA, Imax=40kA
Lumen Design Method

Indoor Lighting Lumen Count

Calculate required number of LED luminaires to achieve target illuminance (Lux) in indoor rooms.

500 Lux Target @ 50 m² Area:52,083 Lumens Req
Fixture Count (4000lm ea):14 LED Fixtures
Selectivity Margin

Breaker Selectivity Margin

Evaluate overcurrent breaker selectivity coordination ratio to prevent upstream main breaker nuisance trips.

100A Main / 20A Branch (1.5kA):5.0:1 Ratio (PASS)
Coordination:Branch Trips Alone
Zener Voltage Shunt

Zener Voltage Regulator

Calculate series limiting resistor value (Ω) and max Zener diode power dissipation (mW) for shunt regulators.

12V-15V In to 5.1V Zener (50mA):R_s = 125.5 Ω
Zener Dissipation:P_z = 377 mW
θ_SA Thermal °C/W

Heatsink Thermal Sizing

Calculate maximum allowable heatsink thermal resistance (°C/W) to prevent semiconductor thermal destruction.

15W @ 125°C Tj (40°C Ambient):θ_JA = 5.67 °C/W
Required Heatsink:θ_SA ≤ 3.67 °C/W
N = √(L_nH / A_L)

Ferrite Core Inductor Turns

Calculate magnet wire turns count N for toroidal and bobbin ferrite cores using manufacturer A_L inductance factors.

100 µH Target (A_L = 250 nH/t²):100,000 nH
Winding Count:N = 20 Turns
IEEE C57.110 K-Factor

Transformer K-Factor

Calculate K-Factor rating from non-linear load harmonic currents to prevent transformer neutral and core overheating.

Harmonics: 3rd(15%), 5th(25%):K-Factor = 4.01
Recommended Rating:K-4 Transformer
T-Pad & π-Pad Resistors

RF / Audio Attenuator Pad

Calculate resistor values (Ω) for symmetrical T-Pad and Pi-Pad impedance-matched signal attenuators.

6 dB Attenuation @ 50 Ω (T-Pad):K Ratio = 1.995
Resistors:R1=R2=16.6Ω, R3=66.9Ω
kWh = W × h / 1000

Appliance Energy Cost

Daily, monthly and yearly running cost of any appliance with duty cycle and standby draw.

Default load:7.36 kWh/day
Monthly cost:33.12
Fuel = a·P_rated + b·P_load

Generator Fuel Consumption

Diesel, gas and LPG fuel use versus load, with cost per kWh generated.

100 kW set @ 75 kW:21.0 L/h
Specific use:0.280 L/kWh
kVA = kW / PF

Power Factor Penalty

Utility penalty for low power factor, kVA billing comparison and capacitor payback.

500 kW @ 0.78 PF:1,026 / month
Billing model:kVA demand
Payback = cost / savings

LED Savings & Payback

LED retrofit ROI with relamping labor, cooling-load credit and simple payback.

Default retrofit:11.1 months
Annual saving:6,677
kWh = load × days / DoD

Battery Bank Storage

Ah and kWh sizing with autonomy, DoD and lead-acid versus LiFePO4 comparison.

48 V bank:24.2 kWh
Layout:4S × 3P
DC/AC ratio & MPPT window

Grid-Tie Inverter Sizing

DC/AC ratio, clipping loss and MPPT string window matching.

DC/AC 1.20:~0.7% clipping
String range:5–14 modules
cost/mi vs gasoline

EV Range & Charging Cost

EV cost per mile versus gasoline with break-even electricity and fuel prices.

EV cost:$0.051 / mi
Gasoline:$0.117 / mi
VD = 2 × I × R × L

Solar Wire Voltage Drop

PV string and DC cable voltage drop with AWG and mm² selection.

300 V, 9.6 A, 300 ft 6 AWG:0.94% drop
Min size:8 AWG
Tilt from latitude

Solar Tilt & Azimuth

Optimum tilt, true azimuth and winter-solstice row spacing for a site latitude.

40°N year-round:33.5° tilt
Row pitch:3.29 m
T = 1.1 × R × C

555 Timer Monostable

One-shot pulse width from R and C with trigger and loading checks.

100 kΩ, 10 µF:1.10 s
Formula:T = 1.1 R C
C_eq & voltage sharing

Capacitor Series & Parallel

Equivalent capacitance and voltage sharing across series capacitors.

Default network:319.7 µF
Check:80% voltage rule
L_eq with coupling k

Inductor Series & Parallel

Equivalent inductance with mutual coupling and coupling-factor extraction.

Series aiding, k = 0.9:38 µH
Mutual M:9 µH
Γ = (ZL − Z0) / (ZL + Z0)

VSWR & Return Loss

Reflection coefficient, VSWR, return loss and mismatch loss.

VSWR 2:1:9.54 dB RL
Reflected power:11.1%
Z0, ε_eff

Microstrip Impedance

Characteristic impedance and effective dielectric constant from PCB trace geometry.

FR-4, 3 mm over 1.6 mm:50.2 Ω
ε_eff:3.33
λ = c / f

Dipole Antenna Length

Half-wave dipole and quarter-wave lengths with velocity-factor adjustment.

146 MHz dipole:0.975 m
7.1 MHz dipole:65.9 ft
FSPL = 20 log(4πd/λ)

Friis & Path Loss

Free-space path loss, received power and link margin for an RF link.

2.4 GHz, 1 km:FSPL 100.05 dB
Link margin:34.9 dB