4/0 75*C Ampacity?

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Thanks... but still confused as to why the ampacities are different.
 

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mbrooke said:
Thanks... but still confused as to why the ampacities are different.
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You can only compare ampacities where all of the conditions are the same. The first bare ampacity table you posted is based on a 25°C ambient, and a maximum 75°C conductor temperature. The second on a 40°C ambient and 80°C conductor temperature. The first is based on a 50°C rise and the second on a 40°C rise.
 
don_resqcapt19 said:
You can only compare ampacities where all of the conditions are the same. The first bare ampacity table you posted is based on a 25°C ambient, and a maximum 75°C conductor temperature. The second on a 40°C ambient and 80°C conductor temperature. The first is based on a 50°C rise and the second on a 40°C rise.
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Good point.
 
Bare conductors can cool much faster than insulated conductors. Remember that the word "insulation" is used for both resistance to electrons passing through and resistance to heat passing through.
 
Also, there is no insulation to be damaged, so they can get hotter without increased hazard risk.
 
Calculated according IEEE 738/2007 IEEE Standard for Calculating the Current-Temperature of Bare Overhead Conductors for no sun, wind 2ft/s and ε[Emissivity (0.23 to 0.91)]=0.23 the ampacity of 4/0 copper [75oC conductor 25oC air]=487 A
 
581 A it will do this job:)
Over 300oC copper softens and loses mechanical strength.
However above 90 degrees Celsius the surrounding objects can be ignited or damaged by heat - the contacts of the circuit breakers for example
 
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