Sizing cable

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Haji

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In sizing up a cable for current carrying capacity, the terminals temperature need to be taken into account per NEC. But there is no mention of termination temperature in IEC. Why this discrepancy?
Thanks.
 
Haji said:
In sizing up a cable for current carrying capacity, the terminals temperature need to be taken into account per NEC. But there is no mention of termination temperature in IEC. Why this discrepancy?
Thanks.
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I am not very familiar with the IEC however I do know that the Canadian Electrical Code has just recently clarified their code to include the temperature rating of the lugs. In general it makes sense to me the that the weakest link in the circuit should be considered.

If you had a rope that could hold a 1000 lbs and you tied a short piece at the end that could only handle 500 pounds then you would not want to try and haul 1000 pounds with that setup.
 
Dennis Alwon said:
I do know that the Canadian Electrical Code has just recently clarified their code to include the temperature rating of the lugs. .
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Thanks, Dennis. Will you please expand on that by giving examples: cable size prior to the clarification and the same after the clarification for, interestingly, the cable size based on IEC or NEC works out to be the same and I want to know how?
 
Let's take a lug that is rated for a 1/0 wire at 75C. Looking at a 1/0 rated 90C--Based on the NEC T. 310.15(B)(16)-- the wire is rated 170 amps at 90C but only 150 amp at 75C. If the conductor was loaded to its max then there would be a considerable amount of heat being transferred to the terminal. That extra heat could cause a failure in the termination.

Using the 90C wire, we can de-rate from the higher ampacity since the insulation of the conductor is rated for higher temperatures, but the final ampacity would have to be equal to or less than the 75C rating of the terminal.

I am not sure I am answering what you want to know so maybe someone else can help.
 
Dennis Alwon said:
Let's take a lug that is rated for a 1/0 wire at 75C. Looking at a 1/0 rated 90C--Based on the NEC T. 310.15(B)(16)-- the wire is rated 170 amps at 90C but only 150 amp at 75C. If the conductor was loaded to its max then there would be a considerable amount of heat being transferred to the terminal. That extra heat could cause a failure in the termination.
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I do not know if it is correct to choose the size of cable exactly equal to the load current. In the cable sizer program of the previous post, the program chooses at least the next higher size of the cable in such cases............
 
Haji said:
I do not know if it is correct to choose the size of cable exactly equal to the load current. In the cable sizer program of the previous post, the program chooses at least the next higher size of the cable in such cases............
Click to expand...
As long as the load is not continuous then I can use a wire with an ampacity of 100 amps to feed a 100 amp load. If the load is continuous I must multiply the amps by 125%. Of course when we look for the wire that is appropriate for the job we use T. 310.15(B)(16). No calculations necessary. The NEC may not have the same values as the Canadian Electrical Code or the IEC. I did notice that the 2011 NEC changed the value of some of the wire ampacities in the table.
 
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