Question
Assume a power bank of heating resistors is rated at 40KW and is connected to a 240V supply. The resistors operate for more that three hours at a time and are located in an area with an ambient temperature of 86 Degree F. Copper conductors with THWN-2 insulation are to be used to connect the heaters. What size conductors should be used
Answers
Answered by
GPT 3.5
To determine the size of conductors needed, we will consider the current-carrying capacity based on the given power and voltage, and also account for the temperature rating and ambient temperature.
First, let's calculate the current using the power and voltage:
Power (P) = Voltage (V) * Current (I)
40,000 W = 240 V * I
I = 40,000 W / 240 V
I = 166.67 A
Next, we need to determine the current-carrying capacity of the conductor considering the ambient temperature and temperature rating. The table below provides the ampacity values for copper conductors with THWN-2 insulation based on ambient temperature and conductor size:
╔═══════════╦═════════╗
║ Temp (°F) ║ Ampacity ║
╠═══════════╬═════════╣
║ 86°F ║ 90°C ║
╚═══════════╩═════════╝
Since the ambient temperature matches the insulation temperature rating, we can use the ampacity value of 90°C (194°F) for our calculations.
From the table, we select the conductor size based on the ampacity value of 166.67 A. Considering a conservative approach to avoid excessive heating, we should choose a conductor size that can carry at least 200 A.
After consulting a wire ampacity chart, we find that a 3/0 AWG copper conductor has an ampacity of 200 A, which is sufficient for our application.
Therefore, 3/0 AWG copper conductors should be used to connect the heating resistors.
First, let's calculate the current using the power and voltage:
Power (P) = Voltage (V) * Current (I)
40,000 W = 240 V * I
I = 40,000 W / 240 V
I = 166.67 A
Next, we need to determine the current-carrying capacity of the conductor considering the ambient temperature and temperature rating. The table below provides the ampacity values for copper conductors with THWN-2 insulation based on ambient temperature and conductor size:
╔═══════════╦═════════╗
║ Temp (°F) ║ Ampacity ║
╠═══════════╬═════════╣
║ 86°F ║ 90°C ║
╚═══════════╩═════════╝
Since the ambient temperature matches the insulation temperature rating, we can use the ampacity value of 90°C (194°F) for our calculations.
From the table, we select the conductor size based on the ampacity value of 166.67 A. Considering a conservative approach to avoid excessive heating, we should choose a conductor size that can carry at least 200 A.
After consulting a wire ampacity chart, we find that a 3/0 AWG copper conductor has an ampacity of 200 A, which is sufficient for our application.
Therefore, 3/0 AWG copper conductors should be used to connect the heating resistors.