Conductor ampacity

augie47 said:
I don't see much difference from the manner we treat the 90° column in 310.16. 310.17 is simply addresses another location where the conductors ampacity is effected by the environment. The final allowable ampacity is effected by various factors such as ambient and termination limitations.
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Really ?? Id have to respectfully disagree The ampacity of a #12 60c conductor in 310.17 is 30 amps the same value of a 310.16 90c conductor .the ampacity of a 310.17 75 c conductor is higher than a 310.16 90 c conductor . If 110.14(c)(a)(3) was applicable and 310.17 75c ampacity was chosen it would be a clear violstion
 
Jaybone812 said:
Exactly , and branch circuit conductor ampacity comes down to the values listed in 310.16 after applying all the required adjustment factors and required temp rating
. guys don’t understand that circuits less than 100 amps are not always restricted to 60 c ampacity unless the wiring method is restricted 60 c ampacities . For instance specific conductor applications part of 240.4(g) can size their branch circuit conductors to both the terminal temp rating and temp of the equipment in accordance with 110.14(c)(1)(a)(3)


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My point is that with cablebus the Table 310.17 ampacities are used for most installations, even though the code says we can't do that.
 
don_resqcapt19 said:
My point is that with cablebus the Table 310.17 ampacities are used for most installations, even though the code says we can't do that.
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I understood and agreed with your comment , my comment included a typo and when I corrected the typo accidentally deleted the part of my comment saying as much after ‘Exactly ‘ I was just saying and even though 310.16 is the only table the nec allows us to use for branch circuit conductor ampacity, quite a few people in the industry don’t understand how to find the correct ampacity of their conductors based on the temp rating of the wiring method in specific applications . .
 
Jaybone812 said:
What are you even talking about , 310.16 is the only table in the nec we use for the ampacity of our branch circuit conductors . The other tables are used for to find the demand factor that applies when ampacity correction is required. Everything comes down to the ampacity values listed in table 310.16 based on temp rating of the conductors
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What i am talking about is what i said from the beginning. Many electricians here have tried to sqeeze more ampacity out of wires based on their particular wiring method.

For example, removing wire from conduit to place it in free air and using the higher ampacity for the same wires while now using table 310.17. Then they do this without considering ampacity ambient adjustment or conductor bundling ampacity correction and table 310.16.

If i did not read 110.14 C 1, I also would have thought using other tables ampacity without matching table 310.16 after ampere derating would have been correct.

As the picture i sent from the nec book shows, device temperature termination points are tested using table 310.16 and using other tables without reducing ampacity to correspond to this table could result in higher temperatures than allowed
 
Jpflex said:
What i am talking about is what i said from the beginning. Many electricians here have tried to sqeeze more ampacity out of wires based on their particular wiring method.

For example, removing wire from conduit to place it in free air and using the higher ampacity for the same wires while now using table 310.17. Then they do this without considering ampacity ambient adjustment or conductor bundling ampacity correction and table 310.16.

If i did not read 110.14 C 1, I also would have thought using other tables ampacity without matching table 310.16 after ampere derating would have been correct.

As the picture i sent from the nec book shows, device temperature termination points are tested using table 310.16 and using other tables without reducing ampacity to correspond to this table could result in higher temperatures than allowed
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My whole point is 310.17 is not permitted to use for branch circuit conductor ampacity
 
Jaybone812 said:
I understood and agreed with your comment , my comment included a typo and when I corrected the typo accidentally deleted the part of my comment saying as much after ‘Exactly ‘ I was just saying and even though 310.16 is the only table the nec allows us to use for branch circuit conductor ampacity, quite a few people in the industry don’t understand how to find the correct ampacity of their conductors based on the temp rating of the wiring method in specific applications . .
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We know how to find it, but just choose to ignore it based on past experience with the cablebus installations in industrial applications. :)
 
don_resqcapt19 said:
We know how to find it, but just choose to ignore it based on past experience with the cablebus installations in industrial applications. :)
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You’re right even the dude that thinks individual branch circuits that serve a piece of hardwired utilization equipment are not supplied by a outlet only it’s only a termination , actually understands applications in 240.4(g) are not subject to 240.4(d) . So it must be pretty easy to comprehend I guess lol . But there are quite a few guys who love reciting 240.4(d) for everything under 100 amps even though the largest conductor referenced in the rule #10 lol. Idk how I still get surprised anymore lol
 
Jpflex said:
For example, I recall one post here on Mike Holts forum of an electrician trying to justify assigning a higher ampacity to a wire based on NEC table 310.17.

Although he would appear correcect in doing this for the free air conductor wiring method he claimed to have, it would be incorrect according to the opening wording of NEC code 110.14 (C) (1) which states:
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110.14 is titled Electrical Connections.

It has nothing to do with selecting the ampacity of the conductors.

310.14 is titled Ampacity for Conductors.

It directs you how to select the ampacity of conductors. It directs you to 310.15, which directs you to Ampacity Table 310.16 through 310.21.

Selecting an ampacity from Table 310.17 is perfectly acceptable when the conditions specified therein are met.
 
david luchini said:
110.14 is titled Electrical Connections.

It has nothing to do with selecting the ampacity of the conductors.
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So on the one hand I agree, as the ampacity at a termination seems to be a distinct idea or limit from the ampacity for the "run" of the wire. This is not very explicit in the code language, but is clear enough in Annex D, particularly Example D3(a).

On the other hand, 110.14(C) starts off "The temperature rating associated with the ampacity of a conductor shall be selected and coordinated . . .," so it seems to be saying something about how we apply 310.14. It is only the second sentence of 110.14(C) that partially rescinds that first sentence to make the distinction somewhat clear.

I think a lot of the uses of the word "ampacity" in the NEC would be clearer if a few different subterms were defined and used, like "termination ampacity" (what 110.14(C) discusses), "wire ampacity" (the "run" of the wire) and maybe "base ampacity" (a value directly from one of the tables in 310, which may end up as the final answer (termination ampacity) or may be further subject to adjustment or correction (wire ampacity)).

Cheers, Wayne
 
For example, I don't have clarity on the following question:

Say I terminate 90C rated #10 Cu on a 30A 75C rated breaker at one end and 75C rated equipment at the other end, and no ampacity adjustment or correction is required (30C ambient temperature, 3 CCCs in a conduit). What is the "ampacity" of the wire?

I would be inclined to say the wire ampacity is 40A, while the termination ampacity is 35A. [As a separate matter, the maximum allowable OCPD is 30A under 240.4(D) unless 240.4(G) applies, but that is not ampacity.] And then I guess I'd say the overall circuit ampacity (the minimum of all applicable ampacities to all parts of the circuit) is 35A.

But it's certainly possible to read 110.14(C) as saying that the wire ampacity is only 35A. That argument would be that you have to select the 75C temperature rating for the ampacity of the conductor because of the termination rating; the allowance for using the 90C ampacity for adjustment and correction is immaterial, as no such adjustment or correction applies.

Is there any section of the NEC that requires an increased ampacity without also requiring an increased OCPD size? If there is, then the above question could matter for applying that section. If not, then it's primarily an academic question, as under both interpretations the installation is fine.

Cheers, Wayne
 
david luchini said:
110.14 is titled Electrical Connections.

It has nothing to do with selecting the ampacity of the conductors.

310.14 is titled Ampacity for Conductors.

It directs you how to select the ampacity of conductors. It directs you to 310.15, which directs you to Ampacity Table 310.16 through 310.21.

Selecting an ampacity from Table 310.17 is perfectly acceptable when the conditions specified therein are met.
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Exactly once all the required corrections /adjustments of 310.15 are made, we can apply the conductor temp rating 110.14(c)(1) permits based on the application and terminal temperature rating used when sizing your branch circuit conductors by the ampacity values of 310.16


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Jaybone812 said:
Exactly once all the required corrections /adjustments of 310.15 are made, we can apply the conductor temp rating 110.14(c)(1) permits based on the application, when sizing your branch circuit conductors by the ampacity values of 310.16
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You make it sound like one long computation. It's really two separate computations--one is the wire ampacity which just requires looking at 310; the other is termination ampacity, which is covered by 110.14(C).

And sections like 215.2(A)(1) impose different requirements on the necessary values for each--the wire ampacity just has to be at least the calculated load (215.2(A)(1)(b)); while the minimum termination ampacity includes a 125% factor for any portion of the load that is continuous (215.2(A)(1)(a)). Of course, 215.3 imposes a 125% factor on the continuous portion of the load for determining the minimum OCPD size, and then 240.4(B) will require that the wire ampacity be at least 1A more than the next smaller OCPD size (or at least the OCPD size if that is over 800A); either way, that likely is stricter than the requirement of 215.2(A)(1)(b).

Cheers, Wayne
 
david luchini said:
110.14 is titled Electrical Connections.

It has nothing to do with selecting the ampacity of the conductors.

310.14 is titled Ampacity for Conductors.

It directs you how to select the ampacity of conductors. It directs you to 310.15, which directs you to Ampacity Table 310.16 through 310.21.

Selecting an ampacity from Table 310.17 is perfectly acceptable when the conditions specified therein are met.
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The rule in 114.14(C)(1) requires equipment to be listed and marked if it is suitable for use with ampacities other than the Table 310.16 ampacities.
Can you give some examples?
 
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wwhitney said:
You make it sound like one long computation. It's really two separate computations--one is the wire ampacity which just requires looking at 310; the other is termination ampacity, which is covered by 110.14(C).

And sections like 215.2(A)(1) impose different requirements on the necessary values for each--the wire ampacity just has to be at least the calculated load (215.2(A)(1)(b)); while the minimum termination ampacity includes a 125% factor for any portion of the load that is continuous (215.2(A)(1)(a)). Of course, 215.3 imposes a 125% factor on the continuous portion of the load for determining the minimum OCPD size, and then 240.4(B) will require that the wire ampacity be at least 1A more than the next smaller OCPD size (or at least the OCPD size if that is over 800A); either way, that likely is stricter than the requirement of 215.2(A)(1)(b).

Cheers, Wayne
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You’re right my question was not written the correct way I and I apologize, I paraphrased and there are multiple factors to consider before even applying ampacity correction adjustment factors , and everything you said applies , and rhe application is taken into consideration as well , because if 240.4(d)(1-8) applies to the branch circuit used in your application any equipment provisions of 110.14(c) that permit the conductors to be sized using higher than 60c ampacities don’t apply Anyways .
My bad next time i make a technical comment such as this I’ll include all the required information . Thank you for the correction
 
I have never seen equipment marked for use with other than the 310.16 ampacities. Can you give an example?
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No. I'm not sure it's relevant to what I said, though.

A 75deg termination for a maximum #3awg would be rated for 100A.

A 75deg #3awg cu conductor in free air would have an allowable ampacity of 145.

Two separate issues. One doesn't change the other.
 
david luchini said:
No. I'm not sure it's relevant to what I said, though.

A 75deg termination for a maximum #3awg would be rated for 100A.

A 75deg #3awg cu conductor in free air would have an allowable ampacity of 145.

Two separate issues. One doesn't change the other.
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The way I read 110.14(C)(1) is that in those two examples, the ampacity at the termination is not permitted to exceed 100 amps.
It doesn't matter where the ampacity limit it, it limits the current for all of the circuit.
 
don_resqcapt19 said:
The way I read 110.14(C)(1) is that in those two examples, the ampacity at the termination is not permitted to exceed 100 amps.
It doesn't matter where the ampacity limit it, it limits the current for all of the circuit.
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What about a termination with a conductor range of #4-#3/0...

Per 310.16, What would be the ampacity limit of the termination do that it wouldn't exceed its 75 deg rating?
 
david luchini said:
What about a termination with a conductor range of #4-#3/0...

Per 310.16, What would be the ampacity limit of the termination do that it wouldn't exceed its 75 deg rating?
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It depends on the size conductor that is connected to it. That's why we use the 75 degree column; it is the current through the conductor that heats the terminal.
 
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