E2 Conductor Ampacity and Derating 2

Question 1

When more than 3 current-carrying conductors are installed in a conduit, NEC Table 310.15(C)(1) requires a derating factor. What is the correction factor when 7 to 9 conductors are bundled together?

Accepted Answer

0.70

Answer

NEC Table 310.15(C)(1) specifies a 0.70 (70%) adjustment factor when 7 to 9 current-carrying conductors are installed in a raceway or cable.

Question 2

A 4 AWG THHN copper conductor has a 75°C terminal rating. Using NEC Table 310.16, what is the ampacity used for circuit calculations?

Accepted Answer

85A

Answer

NEC Table 310.16 lists 4 AWG THHN copper at 95A for 90°C, but the 75°C column value of 85A governs when terminals are rated 75°C.

Question 3

Which NEC article provides the general rules for conductor ampacity calculations including adjustment and correction factors?

Accepted Answer

Article 310

Answer

NEC Article 310 covers conductors for general wiring, including ampacity tables and the application of adjustment and correction factors.

Question 4

Six current-carrying 12 AWG THHN conductors are installed in a single conduit at an ambient temperature of 30°C. What is the derated ampacity per conductor?

Accepted Answer

15A

Answer

Six conductors require a 0.80 adjustment; 12 AWG THHN at 90°C is 30A, so 30A × 0.80 = 24A, but limited to 20A × 0.80 = 16A at 75°C terminal rating.

Question 5

Under NEC 310.15(E), what is the minimum allowable ampacity for a conductor used as an equipment grounding conductor?

Accepted Answer

It is not required to be derated for bundling

Answer

NEC 310.15(E) states that equipment grounding conductors and neutral conductors that are not current-carrying are not counted for bundling adjustment purposes.

(E2) E2 Commercial Electrical Inspector Practice Test

(E2) E2 Commercial Electrical Inspector Practice Test

E2 Conductor Ampacity and Derating 2