Question 1

What is the minimum copper conductor size required for a 20-amp continuous load in a location with 60°C insulation rating?

Accepted Answer

10 AWG (NEC NEC 310.16). Per NEC 210.19(A)(1), continuous load conductor ampacity must be at least 125% of the load. 20A × 1.25 = 25A minimum. Per Table 310.16, 10 AWG at 60°C = 30A, which satisfies 25A. 12 AWG at 60°C = 20A is insufficient.

Question 2

A 30-amp non-continuous load requires which minimum copper conductor size at 75°C rating?

Accepted Answer

10 AWG (NEC NEC 310.16). Per NEC 310.16, Table 310.16, 75°C column: 10 AWG copper = 35A. Since the load is 30A non-continuous, a conductor rated for 30A or higher is required. 10 AWG at 75°C = 35A, which exceeds the 30A requirement.

Question 3

What is the minimum aluminum conductor size for a 40-amp load at 90°C insulation rating?

Accepted Answer

6 AWG (NEC NEC 310.16). Per NEC 310.16, Table 310.16, 90°C column for aluminum: 8 AWG = 50A, 6 AWG = 60A. For a 40-amp load, 6 AWG aluminum at 90°C = 60A satisfies the requirement. 8 AWG at 90°C = 50A is also acceptable, but 6 AWG is the safer standard choice for 40A at 90°C.

Question 4

A 50-amp continuous load requires which minimum copper conductor size at 75°C rating?

Accepted Answer

4 AWG (NEC NEC 310.16). Per NEC 310.16 and 125% continuous load rule: 50A × 1.25 = 62.5A required conductor rating. Table 310.16, 75°C column: 4 AWG copper = 85A, which exceeds 62.5A. Therefore, 4 AWG is the minimum required.

Question 5

Determine the minimum copper conductor size for a 100-amp continuous load at 90°C rating.

Accepted Answer

1/0 AWG (NEC NEC 310.16). Per NEC 310.16 and 125% continuous load rule: 100A × 1.25 = 125A required conductor rating. Table 310.16, 90°C column for copper: 1 AWG = 145A, 1/0 = 170A. Since 125A is needed, 1/0 AWG at 90°C = 170A is the minimum that satisfies the requirement.

Practice Questions: Conductor Sizing