question asks
what is the ampacity or AMP of a 4 AWG THHN aluminum conductor?
Answer:
75 amps * 0.85 = 63.75 amps
Step-by-step explanation:
1. There are some thick wires inside a long metal box.
2. Each wire can carry electricity.
3. The wires are made of aluminum.
4. Each wire is 4 AWG size.
5. The wires are THHN type.
6. There are 4 wires bundled together in each cable.
7. There are several cables in the metal box.
8. The cables fill up the metal box but do not overflow.
9. What is the maximum electric current each wire can safely carry?
10. Round the final number to the nearest whole number.
The ampacity of a 4 AWG THHN aluminum conductor is 75 amps at 75°C (167°F) in free air.
The ambient temperature correction factor for an eight-foot solid metal cover is 0.85.
The ampacity of each conductor is therefore:
75 amps * 0.85 = 63.75 amps
another way :
- There are several 4-conductor cables installed in a ladder cable tray
- Each cable has 4 conductors that are 4 AWG THHN aluminum
- The cable tray has an 8 foot solid metal cover
- We need to calculate the ampacity of each conductor without exceeding the fill of the cable tray
To determine the ampacity, we'll need to refer to the National Electrical Code (NEC). A few key points:
- 4 AWG THHN aluminum has an ampacity of 100 amps in free air per Table 310.15(B)(16) (based on the 75°C column)
- Since this is in a ladder cable tray, we derate the ampacity to 80% per NEC 392.80(A)(1)(c).
- The ampacity needs to be further derated to the allowable fill percentage of the cable tray per NEC 392.22(A). Let's assume a fill percentage of 40% which requires an additional derating to 0.7 per Table 392.22(A)
So the final derated ampacity is:
100 amps x 0.8 x 0.7 = 56 amps
Therefore, the final ampacity of each 4 AWG THHN aluminum conductor is 56 amps (rounded to the nearest whole number).