Load calculation question from Mike Holt video?

[Rolson]

I had some questions regarding this image from a Mike Holt video. Now according to NEC 2014 a number 12 copper wire at 60C is rated at 20amps. So how can you carry at 23 amp load on this 20 amps worth of wire. After following the note to 240.4 (D) we see

Also according to the code section 240.4 (D) After all correction factors are taken into account a 12AWG must not exceed 20 amps unless stated in 240.4 (E) or (G). E should have no effect unless it is a tap situation. So that leads up to 240.4 (G) which states

That the code can be altered for air condition equipment and refer to 440 parts 3 and 4 which states

We must have some more information on the problem but also we must have 125% for our branch circuit conductors so that 23 must be sized to 28.75.

On another code section that should be taken into account would be 110.14 (C) (1) which talks about electrical connections and temperature limitations. The code states "The temperature rating associated with the ampacity of a conductor shall be selected rating of any connected termination, conductor, or device. Conductors with the temperature rating higher than specified for terminations shall be permitted to use for ampacity adjustment, correction, or both."

Still on the same code section it states unless all the equipment is "listed or marked" the conductors should be sized off of 310.15 (B)(16). Also a termination provision of equipment 100 amps or less or marked 14AWG-1AWG should be sized off of the 60C column unless it marked differently as above in 110.14(C) or some exceptions that are not related to this.

If it over 100amps or bigger than 1AWG you can use the 75C column.

So where is this 25amps on 12AWG at 60C coming from?

 

[Carultch]

I had some questions regarding this image from a Mike Holt video. Now according to NEC 2014 a number 12 copper wire at 60C is rated at 20amps. So how can you carry at 23 amp load on this 20 amps worth of wire. After following the note to 240.4 (D) we see

Also according to the code section 240.4 (D) After all correction factors are taken into account a 12AWG must not exceed 20 amps unless stated in 240.4 (E) or (G). E should have no effect unless it is a tap situation. So that leads up to 240.4 (G) which states

That the code can be altered for air condition equipment and refer to 440 parts 3 and 4 which states

We must have some more information on the problem but also we must have 125% for our branch circuit conductors so that 23 must be sized to 28.75.

On another code section that should be taken into account would be 110.14 (C) (1) which talks about electrical connections and temperature limitations. The code states "The temperature rating associated with the ampacity of a conductor shall be selected rating of any connected termination, conductor, or device. Conductors with the temperature rating higher than specified for terminations shall be permitted to use for ampacity adjustment, correction, or both."

Still on the same code section it states unless all the equipment is "listed or marked" the conductors should be sized off of 310.15 (B)(16). Also a termination provision of equipment 100 amps or less or marked 14AWG-1AWG should be sized off of the 60C column unless it marked differently as above in 110.14(C) or some exceptions that are not related to this.

If it over 100amps or bigger than 1AWG you can use the 75C column.

So where is this 25amps on 12AWG at 60C coming from?

View attachment 12971

The only way that can be correct is if terminations on both sides are listed and marked otherwise for 75C, which is the most likely case practically in the field.

 

[Smart $]

...but also we must have 125% for our branch circuit conductors so that 23 must be sized to 28.75....

That is not correct. A "minimum circuit ampacity" rating already includes the 125%.

If I read the copyright correctly, it is 2014... which makes it a violation for 60°C termination... but that would have been okay back under 2008 cycle when #12 @ 60°C was rated 25A. Perhaps the copyright year was updated but wire size being compliant was overlooked.

 

[Rolson]

Thanks for the insight on this. The video was suppose to be based on 2014 but wanted to see if I was overlooking something.

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[Rolson]

The only way that can be correct is if terminations on both sides are listed and marked otherwise for 75C, which is the most likely case practically in the field.

Now does all the terminations and devices have to be rated 75C?

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[Carultch]

Now does all the terminations and devices have to be rated 75C?

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All terminations that are in direct contact with that particular section of conductor.

Both the breaker, and the load equipment. And any taps you might make, such as an insulation piercing connector mid-tapping the wiring.
Once you put a 60 C termination in the system, or 60C wiring, the ampacity comes from the 60C column of the NEC.


An interesting point about wire with a 60C rating. You have to connect it to a device that is rated to accept it. Not enough to just derate it to its 60C ampacity. If connecting to a device that is only rated at 75C, you need either 75C or 90C wiring. That is why you see equipment dual rated as 60C/75C. That was a mystery to me, when I first saw it on a datasheet.

 

[Rolson]

All terminations that are in direct contact with that particular section of conductor.

Both the breaker, and the load equipment. And any taps you might make, such as an insulation piercing connector mid-tapping the wiring.
Once you put a 60 C termination in the system, or 60C wiring, the ampacity comes from the 60C column of the NEC.


An interesting point about wire with a 60C rating. You have to connect it to a device that is rated to accept it. Not enough to just derate it to its 60C ampacity. If connecting to a device that is only rated at 75C, you need either 75C or 90C wiring. That is why you see equipment dual rated as 60C/75C. That was a mystery to me, when I first saw it on a datasheet.

I noticed the dual rating on breakers for example. Now there is another rating of 40C is that for ambient temperature of install to keep the trip curve correct?

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