Phần hướng dẫn bên dưới chưa có bằng tiếng Việt nên được hiển thị bằng tiếng Anh. Bản thân máy tính đã được dịch đầy đủ.
Cách sử dụng máy tính này
- Choose what to solve for: amps, watts or volts.
- Choose the circuit type. Household outlets are single-phase AC.
- Enter the two known values and, for AC, the power factor (1.0 for resistive loads like heaters; 0.8–0.95 for motors).
Công thức
Real power depends on voltage, current and, in AC circuits, the power factor between them. Three-phase power uses line-to-line voltage and a factor of √3.
DC: P = V × I
Single-phase AC: P = V × I × PF
Three-phase AC: P = √3 × V × I × PF
Example
- A 1,800 W heater on 120 V (PF 1): I = 1,800 / 120 = 15 A.
- That's the full rating of a 15 A circuit; continuous loads should stay at or below 80% (12 A).
Câu hỏi thường gặp
What is the 80% rule?
In the US NEC, continuous loads (3+ hours) shouldn't exceed 80% of a breaker's rating. A 20 A circuit should carry no more than 16 A continuously.
What is power factor?
The ratio of real power (W) to apparent power (VA). Inductive loads such as motors draw more current than their wattage alone suggests.
What voltage should I use?
Common supplies are 120/240 V in North America, 230 V in Europe and much of the world, and 100 V in Japan. Three-phase systems are typically 208, 400 or 480 V line-to-line.