Mike Holts illustrated guide

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Beto59

Member
Location
Midland,Texas
Occupation
Journeyman Electrician
Based on 2017 guide pg.260, ampacity adjustment is based on conductor's temperature insulation, not terminal temperature. Yet on pg. 261 it has reference to temp. Listing of terminal. "Bit confused"
 

Dennis Alwon

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Staff member
Location
Chapel Hill, NC
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Retired Electrical Contractor
Most of us do not have mike holt 2017 guide so we cannot see the actual wording. However as xformer stated both terminal and temp of the conductor comes into play.

For instance, if you have 90C wire and the terminals or the equipment that you connect to are rated 75C then you must use the 75C rating. You can however use the 90C rating if you have to de-rate but the final ampacity cannot be larger than the 75C rating.
 

don_resqcapt19

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Staff member
Location
Illinois
Occupation
retired electrician
The ampacity adjustment and or correction is based on the temperature rating of the conductor.

However, the ampacity that you can use that conductor at in the circuit may be limited by the rating of the terminations.

They are really two independent issues.
 

mikeames

Senior Member
Location
Germantown MD
Occupation
Teacher - Master Electrician - 2017 NEC
And to add more confusion, even if you have 90c rated conductors and 90c rated terminals, you would still need 90c rated equipment to use the 90c ampacity in the circuit. 90c terminals are common but 90c equipment is not.
 

Carultch

Senior Member
Location
Massachusetts
And to add more confusion, even if you have 90c rated conductors and 90c rated terminals, you would still need 90c rated equipment to use the 90c ampacity in the circuit. 90c terminals are common but 90c equipment is not.

Correct. It is generally when you terminate on separately-installed connectors in an otherwise-empty enclosure, that you get to take credit for a 90C rating of the terminals. Or in an enclosure that contains nothing but busbars. Everything inside the enclosure needs a 90C rating to take credit for 90C terminations.

It is very common that the lug is marked for 90C, but built within equipment that isn't. 75C is the most common rating of equipment. There is a line drawn at 100A and less, such that 60C is the default for 100A and less, while 75C is the default over 100A. Think of it as a burden of proof, for the manufacturer to have listing and labeling that spells out the 75C rating. Cases where the 60C rating governs a design are usually more academic than practical, because most equipment carries a 75C listing to override this default.
 

Carultch

Senior Member
Location
Massachusetts
Cases where the 60C rating governs a design are usually more academic than practical, because most equipment carries a 75C listing to override this default.

One notable exception to that, is anytime you use NM cable, commonly known as Romex. For this, the NEC specifies a requirement to use 60C terminations.
 
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