CSLB C-10 Electrical ContractorPlanning and EstimatingMedium
A technician is performing a material takeoff for a commercial kitchen. The plan calls for wiring a 208V, 3-phase, 3-wire circuit to a 10 kW oven. The circuit will use three current-carrying conductors. What is the approximate continuous current draw of this oven?
- A57.7A
- B34.7A
- C27.7A
- D48.1A
Show answer & explanationAnswer & explanation
Correct answer: C. 27.7A
For a 3-phase circuit, the current (I) is calculated using the formula: I = P / (V * √3), where P is power in watts, V is line-to-line voltage, and √3 is approximately 1.732. Given: P = 10 kW = 10,000 W, V = 208V. I = 10,000 W / (208V * 1.732) = 10,000 W / 360.256 ≈ 27.76 A. Since this is a continuous load (oven), the OCPD and conductor sizing would further require a 125% multiplier, but the question only asks for the continuous current draw.
Why the other options are wrong
- A. Incorrect. This value might result from using 208V as a single-phase voltage in an incorrect formula.
- B. Incorrect. This value might result from incorrect voltage or formula application.
- D. Incorrect. This value might result from using the single-phase formula or incorrect voltage.
3-Phase Current Calculation
Calculating the current (amperes) in a 3-phase circuit given the power (watts) and line-to-line voltage, using the formula I = P / (V * √3).
- Applies to balanced 3-phase loads.
- √3 (square root of 3) is approximately 1.732.
- Power (P) must be in watts (W) and voltage (V) in volts (V).
Memory trick: Power is Root-Three times Voltage, Current, and Power Factor.