Why Unit Conversions Matter in Electrical Work
Electrical calculations involve quantities that span many orders of magnitude — from microfarads in capacitors to megawatts in power plants. A single unit conversion error can mean the difference between a working circuit and a dangerous one. This guide gives you the key conversions every electrician and engineer needs.
SI Prefix Quick Reference
| Prefix | Symbol | Multiplier | Example |
|---|---|---|---|
| Mega | M | × 1,000,000 | 1 MΩ = 1,000,000 Ω |
| Kilo | k | × 1,000 | 1 kV = 1,000 V |
| — | — | × 1 | Base unit |
| Milli | m | × 0.001 | 1 mA = 0.001 A |
| Micro | μ | × 0.000001 | 1 μF = 0.000001 F |
| Nano | n | × 0.000000001 | 1 nF = 0.000000001 F |
Current Conversions (電流の換算)
The base unit of current is the Ampere (A).
- 1 A = 1,000 mA (milliamps)
- 1 mA = 0.001 A
- 500 mA = 0.5 A
- 1 A = 1,000,000 μA (microamps)
Example: A circuit draws 250 mA. Convert to Amps: 250 ÷ 1,000 = 0.25 A
Voltage Conversions (電圧の換算)
The base unit of voltage is the Volt (V).
- 1 kV = 1,000 V
- 1 V = 1,000 mV
- 6,600 V = 6.6 kV (common Japanese distribution voltage)
- 100 V = 0.1 kV (standard Japanese household voltage)
Resistance Conversions (抵抗の換算)
The base unit of resistance is the Ohm (Ω).
- 1 MΩ = 1,000,000 Ω = 1,000 kΩ
- 1 kΩ = 1,000 Ω
- 1 Ω = 1,000 mΩ
Example: An insulation tester reads 20 MΩ. In ohms: 20 × 1,000,000 = 20,000,000 Ω
Power Conversions (電力の換算)
- 1 kW = 1,000 W
- 1 MW = 1,000 kW = 1,000,000 W
- 1 W = 1 J/s (joule per second)
- 1 horsepower (HP) ≈ 746 W
Example: A motor is rated at 5.5 kW. Convert to watts: 5.5 × 1,000 = 5,500 W
Capacitance Conversions (静電容量の換算)
- 1 F (Farad) = 1,000 mF = 1,000,000 μF
- 1 μF = 1,000 nF = 1,000,000 pF
- 100 μF = 0.0001 F
Energy Conversions (エネルギーの換算)
| From | To | Multiply by |
|---|---|---|
| kWh | Joules (J) | 3,600,000 |
| kWh | MJ | 3.6 |
| Wh | Joules | 3,600 |
| J | Wh | ÷ 3,600 |
Practical Conversion Tips
- Always write out units in full during calculations to catch errors early.
- When using formulas, ensure all quantities are in base units (A, V, Ω, W) before calculating.
- Convert your answer to a convenient prefix at the end (e.g., 0.0025 A → 2.5 mA).
- Double-check meter readings — a multimeter set to mA reads differently than one set to A.