A commercial kitchen is being renovated, and several new 4 kW, 208 V, single-phase electric ovens are being installed. Each oven is connected to its own dedicated circuit. What is the minimum size of THHN copper conductor required for each oven's branch circuit? (Refer to CEC Table 2 and Table D1. Assume two current-carrying conductors in EMT at 30°C ambient).

Question: A commercial kitchen is being renovated, and several new 4 kW, 208 V, single-phase electric ovens are being installed. Each oven is connected to its own dedicated circuit. What is the minimum size of THHN copper conductor required for each oven's branch circuit? (Refer to CEC Table 2 and Table D1. Assume two current-carrying conductors in EMT at 30°C ambient).

Answer options:

• 10 AWG ✅ 8 AWG
• 6 AWG
• 4 AWG

Correct answer: 8 AWG

Explanation: First, calculate the current: I = P/V = 4000 W / 208 V = 19.23 A. Since this is likely a continuous load, multiply by 125%: 19.23 A * 1.25 = 24.04 A. From CEC Table 2, for copper THHN conductors with an 90°C rating, 10 AWG is rated for 35 A, and 8 AWG for 50 A. As this needs a 30A breaker, which 10 AWG (35A) supports, the minimum conductor is 10 AWG. However, for practical purposes and potential continuous loads, oversizing slightly is common. If considering a 30A breaker, 10AWG is suitable. Let's re-evaluate based on the options, and typical breaker selection. A 30A breaker would be used, so no more than 24A continuous (80% of 30A). 10 AWG is rated for 35 A, so it's technically sufficient for 24.04 A load. Given the options, 8 AWG is a common choice for this load size to reduce voltage drop or provide margin, but 10 AWG meets the ampacity requirement. Let's re-evaluate the question and find the best fit. For a 20A continuous load, a 30A breaker is often utilized. A 10 AWG conductor (rated for 35A at 90°C) is suitable for a 30A breaker. Therefore, 10 AWG is the minimum. However, considering heating appliances, often the maximum overcurrent protection is used as the basis. From Rule 8-104 (2)(b) for continuous loads, the branch circuit must be rated for 125% of the continuous load. So, 1.25 * 19.23 A = 24.04 A. A 25A or 30A overcurrent device would be selected. A 10 AWG conductor is rated for 35A (Table 2 for 90°C). Thus, 10 AWG is the minimum required size.