Wire Ampacity

[Alwayslearningelec]

I was listening to the 2023 fundamentals NEC calculation chapter 2 starting at 21:16.

It was referring to 4 wires in raceway. He was doing the adjustments but giving a different ampacity to the wire in the conduit and the wire in the box @ the terminals.

That’s correct to have two different ampacities for same wire at different points?

When using adjustment and correction and it's a continuous load you don't use 125% for the portion in the raceway?

 

[charlie b]

Yes, a run can have more than one ampacity assigned for different portions of a run. That can enable you to use different wire sizes for different portions of the run.

The concepts of continuous loads and adjustments/corrections are unrelated. You calculate the load taking continuous and non-continuous loads into account. Then you select wire sizes with sufficient ampacity for that load. The value of ampacity will depend on conditions of installation, including the use of conduit. Then you select a breaker capable of protecting the wires.

 

[infinity]

It was referring to 4 wires in raceway. He was doing the adjustments but giving a different ampacity to the wire in the conduit and the wire in the box @ the terminals.

Since you mentioned "4 wires in a raceway" one would assume that there were 4 CCC's, otherwise there would be no derating required.

 

[don_resqcapt19]

I was listening to the 2023 fundamentals NEC calculation chapter 2 starting at 21:16.

It was referring to 4 wires in raceway. He was doing the adjustments but giving a different ampacity to the wire in the conduit and the wire in the box @ the terminals.

That’s correct to have two different ampacities for same wire at different points?

When using adjustment and correction and it's a continuous load you don't use 125% for the portion in the raceway?

Very often the ampacity of the conductors after the application of any required adjustment and/or corrections will exceed the 75°C ampacity as shown in Table 310.16. However, most equipment terminations limit you to the 75°C or sometimes the 60°C ampacity.

 

[wwhitney]

The concepts of continuous loads and adjustments/corrections are unrelated.

They are actually related. In the portions of the circuit where ampacity adjustment/correction apply (the run of the wire), there is no continuous load factor. The wire ampacity is itself a continuous rating. In the portions of the circuit where you need to use a 125% continuous load factor (terminations that are not 100% rated), you do not need to apply ampacity adjustment/correction.

Really "wire ampacity" and "termination ampacity" are two different but related concepts, and the NEC should use two different terms for them.

Cheers, Wayne