In a conduit with 9 conductors, Load #3 uses 6 AWG and the 133°F high-temperature rating applies to its current-carrying capacity. What is the current rating of Load #3 wire according to the problem data?

In a conduit with 9 conductors, Load #3 uses 6 AWG and the 133°F high-temperature rating applies to its current-carrying capacity. What is the current rating of Load #3 wire according to the problem data?

• A. 32
• B. 26
• C. 43
• D. 37

Answer: (D)

The concept being tested is derating ampacity when multiple current-carrying conductors are in a conduit and using the correct temperature rating for the insulation. First, the 133°F rating tells you which ampacity column to use for the conductor. For the 6 AWG conductor in this problem, you use the corresponding ampacity from the table that matches that temperature rating (the 60°C column is the typical match for a 133°F insulation rating). Second, count the current-carrying conductors in the conduit. With 9 conductors in play, you must apply the derating factor for that number of conductors. The NEC specifies a reduction factor for more than three current-carrying conductors in a raceway or cable; for 7–9 conductors, that factor reduces the base ampacity accordingly. Third, multiply the base ampacity (from the 60°C column for 6 AWG) by the derating factor for 9 conductors. The result, using the problem’s data, comes out to 37 A, which matches Load #3’s current rating in the given data. In short: the 133°F rating fixes the starting ampacity, the nine conductors trigger a derating, and applying that derating yields the 37 A value.

The concept being tested is derating ampacity when multiple current-carrying conductors are in a conduit and using the correct temperature rating for the insulation.

First, the 133°F rating tells you which ampacity column to use for the conductor. For the 6 AWG conductor in this problem, you use the corresponding ampacity from the table that matches that temperature rating (the 60°C column is the typical match for a 133°F insulation rating).

Second, count the current-carrying conductors in the conduit. With 9 conductors in play, you must apply the derating factor for that number of conductors. The NEC specifies a reduction factor for more than three current-carrying conductors in a raceway or cable; for 7–9 conductors, that factor reduces the base ampacity accordingly.

Third, multiply the base ampacity (from the 60°C column for 6 AWG) by the derating factor for 9 conductors. The result, using the problem’s data, comes out to 37 A, which matches Load #3’s current rating in the given data.

In short: the 133°F rating fixes the starting ampacity, the nine conductors trigger a derating, and applying that derating yields the 37 A value.