wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
Take the case of installing a 100A breaker (75C terminations), #1 Al XHHW-2 (75C ampacity is 100A) for 4', a separate splice box with 90C connectors to #2 Al XHHW-2 (90C ampacity is 100A), etc. I understand this is generally accepted as a way to utilize the full 90C ampacity of a conductor (the #2 Al XHHW-2 in this example).
How does that practice square with the interpretation of the first sentence of 110.14(C) where landing the 90C-rated #1 Al conductor on the 75C breaker reduces its ampacity to 100A? If the temperature rating associated with the #1 Al is now reduced to 75C (except for ampacity correction and adjustment per the second sentence of 110.14(C)), then since the first sentence mentions "any connected . . . conductor", the #2 Al temperature rating would be likewise limited to 75C via its connection to the 75C limited #1 Al.
But if you view the termination limits as separate limits that apply per termination, rather than affecting the conductor ampacity, there's no problem. And if the goal of the rules is to ensure that no point along the circuit will have a temperature exceeding the temperature rating of any equipment at that point, that point of view is in accordance with the physics.
Cheers, Wayne
How does that practice square with the interpretation of the first sentence of 110.14(C) where landing the 90C-rated #1 Al conductor on the 75C breaker reduces its ampacity to 100A? If the temperature rating associated with the #1 Al is now reduced to 75C (except for ampacity correction and adjustment per the second sentence of 110.14(C)), then since the first sentence mentions "any connected . . . conductor", the #2 Al temperature rating would be likewise limited to 75C via its connection to the 75C limited #1 Al.
But if you view the termination limits as separate limits that apply per termination, rather than affecting the conductor ampacity, there's no problem. And if the goal of the rules is to ensure that no point along the circuit will have a temperature exceeding the temperature rating of any equipment at that point, that point of view is in accordance with the physics.
Cheers, Wayne