Help!!!!!

[wwhitney]

I see nothing that actually changes the ampacity when you use the exception.

I would say the phrase "the higher ampacity shall be permitted to be used" has the effect of changing the ampacity. Since "used" is unlimited, we can use the higher ampacity for all purposes.

Just like a lot of other rules, the exception simply permits the conductor to be protected with an OCPD rated higher than the actual conductor ampacity.
The small conductor is a tap and must be installed per the tap rules.

Whenever the bolded portion is true, there is no tap (assuming the whole thing isn't a tap). So if 310.14(A)(2) Exception covers the case of a lower ampacity due to a reduction in conductor size, then there is no tap.

Anyway, because of this sloppy wording, I submitted a PI to change the start of the exception to "Where different ampacities apply to portions of a circuit of identical conductor size,"

Cheers, Wayne

 

[jim dungar]

A straightforward if very naive interpretation of the current wording of 310.14(A)(2) Exception is that if you put 10' of #12 in a circuit next to 90' of 100A conductor, the exception promotes the ampacity of the #12 to 100A. In which case there's no tap, just some #12 with an unreasonably high ampacity.

I think we just need to add the words "of the same size conductor" to the phrase "portions of a circuit" to rule this out.

Cheers, Wayne

As soon as you add the #12 conductor you have created a tap and the upstream OCP will likely be limited to 20A. You cannot ignore all of the rules in 240.

 

[don_resqcapt19]

I would say the phrase "the higher ampacity shall be permitted to be used" has the effect of changing the ampacity. Since "used" is unlimited, we can use the higher ampacity for all purposes.


Whenever the bolded portion is true, there is no tap (assuming the whole thing isn't a tap). So if 310.14(A)(2) Exception covers the case of a lower ampacity due to a reduction in conductor size, then there is no tap.

Anyway, because of this sloppy wording, I submitted a PI to change the start of the exception to "Where different ampacities apply to portions of a circuit of identical conductor size,"

Cheers, Wayne

Once again, we will not be agreeing...there is no way that the reduced ampacity, either as a result of ampacity adjustment and/or correction, or a smaller conductors is not a tap.
I would expect that the PI gets resolved, but we will find out.
Corrected to add missing word "not"

 

[wwhitney]

As soon as you add the #12 conductor you have created a tap and the upstream OCP will likely be limited to 20A. You cannot ignore all of the rules in 240.

Not if the meaning of 310.14(A)(2) Exception is that the ampacity of the #12 conductor gets promoted to the higher value. Then there is no tap, as all the conductors are of sufficient ampacity.

Again, I don't believe that's the intention, that 310.14(A)(2) Exception applies to a reduction in conductor size. But the current wording doesn't make that distinction, as Don pointed out.

Cheers, Wayne

 

[wwhitney]

there is no way that the reduced ampacity, either as a result of ampacity adjustment and/or correction, or a smaller conductors is a tap.

Is that a typo? Because it sounds like you are agreeing with me.

To back up a minute, what is the point of 310.14(A)(2) Exception? My understanding it is to cover examples like the following branch circuit (circuit elements in order):

(A) 50A OCPD
(B) 10' of 90C #8 Cu at 30C ambient with 7-9 CCCs (in isolation, 38.5A adjusted ampacity)
(C) 90' of 90C #8 Cu at 30C ambient with 1-3 CCCs (55A ampacity)
(D) Utilization Equipment

310.14(A)(2) Exception promotes the ampacity of section (B) to 55A, and Articles 240 and 210 are complied with. No tap, correct?

OK, so if I change (B) to 10' of #12 Cu at 30C ambient with 1-3 CCCs (30A ampacity), what changes, code wise? Assuming a literal interpretation of the wording of 310.14(A)(2) Exception, so that it still applies.

Cheers, Wayne

 

[wwhitney]

The exception was carefully drafted not to use the words "adjustment" or "correction" which would have limited the application of the exception. The CMP chose to use the term "different ampacities" which makes it apply no matter why there is a different ampacity.

What exact point were you trying to make with the above observation? Presumably it wasn't to lead me down the rabbit hole that consideration of different conductor size led me to. : - )

Are there any reasons for different ampacity, other than different size, aluminum vs copper, different insulation temperature, and adjustment and correction?

Cheers, Wayne

 

[don_resqcapt19]

What exact point were you trying to make with the above observation? Presumably it wasn't to lead me down the rabbit hole that consideration of different conductor size led me to. : - )

Are there any reasons for different ampacity, other than different size, aluminum vs copper, different insulation temperature, and adjustment and correction?

Cheers, Wayne

It was simply to address the common misconception that the exception only applies to ampacity correction, and not to ampacity adjustment. This concept is found in post 7, and is a common view.

 

[wwhitney]

It was simply to address the common misconception that the exception only applies to ampacity correction, and not to ampacity adjustment. This concept is found in post 7, and is a common view.

Thanks you. So now I've taken it a bit further, to observe that the present language also covers (intentionally or not) ampacity difference due to change in size, change in insulation temperature, or change in material. Which I hope you can agree is what the words literally say, whether or not you see that as a problem or as requiring a PI.

Cheers, Wayne

 

[don_resqcapt19]

Is that a typo? Because it sounds like you are agreeing with me.

To back up a minute, what is the point of 310.14(A)(2) Exception? My understanding it is to cover examples like the following branch circuit (circuit elements in order):

(A) 50A OCPD
(B) 10' of 90C #8 Cu at 30C ambient with 7-9 CCCs (in isolation, 38.5A adjusted ampacity)
(C) 90' of 90C #8 Cu at 30C ambient with 1-3 CCCs (55A ampacity)
(D) Utilization Equipment

310.14(A)(2) Exception promotes the ampacity of section (B) to 55A, and Articles 240 and 210 are complied with. No tap, correct?

OK, so if I change (B) to 10' of #12 Cu at 30C ambient with 1-3 CCCs (30A ampacity), what changes, code wise? Assuming a literal interpretation of the wording of 310.14(A)(2) Exception, so that it still applies.

Cheers, Wayne

yes typo...I left the word "not" out of my statement
Once again, I don't see the exception as changing the ampacity of the lower ampacity conductor...it very clearly permits the higher ampacity to be used, but does not actually change the ampacity. That is just like the rule in 240.4(B)...that does not change the conductor ampacity...it just permits the conductor to be protected with an OCPD that exceeds the conductor ampacity.

Your example of using 12 AWG in the circuit would be a violation of the small conductor rule the exception does not change that rule

However for larger conductors that would not apply.

I think the PI should be:

Exception:
Where different ampacities result from ampacity adjustment and/or correction and apply to portions of a circuit, the higher ampacity shall be permitted to be used if the total portion(s) of the circuit with lower ampacity does not exceed the lesser of 3.0 m (10 ft) or 10 percent of the total circuit.

 

[wwhitney]

Once again, I don't see the exception as changing the ampacity of the lower ampacity conductor...it very clearly permits the higher ampacity to be used, but does not actually change the ampacity. That is just like the rule in 240.4(B)...that does not change the conductor ampacity...it just permits the conductor to be protected with an OCPD that exceeds the conductor ampacity.

Certainly I agree on 240.4(B).

But 310.14(A)(2) Exception doesn't say anything about OCPD or any specific purpose. It says the higher ampacity "shall be permitted to be used." So show me any NEC section that makes a requirement based on ampacity, and I'll say "310.14(A)(2) Exception lets us use the higher ampacity for that."

[As an aside, we once had an exchange on whether 310.12 changes ampacity or not. What is your present take on that?]

Your example of using 12 AWG in the circuit would be a violation of the small conductor rule

Yes, very nice. I should have been using #8 AWG in my examples. : - )

I think the PI should be:

I was just thinking of that as an alternative. Do you want to submit it or should I adjust mine? I'm happy to, but I expect your submission would carry more weight.

Thanks,
Wayne

 

[don_resqcapt19]

Certainly I agree on 240.4(B).

But 310.14(A)(2) Exception doesn't say anything about OCPD or any specific purpose. It says the higher ampacity "shall be permitted to be used." So show me any NEC section that makes a requirement based on ampacity, and I'll say "310.14(A)(2) Exception lets us use the higher ampacity for that."

[As an aside, we once had an exchange on whether 310.12 changes ampacity or not. What is your present take on that?]


Yes, very nice. I should have been using #8 AWG in my examples. : - )


I was just thinking of that as an alternative. Do you want to submit it or should I adjust mine? I'm happy to, but I expect your submission would carry more weight.

Thanks,
Wayne

I don't see the exception in question here, the round up rule in 240.4(B), or the rule in 310.12 as changing the ampacity of the conductors...those rules simply permit the conductors to be protected at a rating that exceeds their ampacity under the conditions specified in those sections.

Many think that the rule in 240.4(B) does change the conductor ampacity and because so many code users thought (think) that, the rules in 240.21 were changed to specify that the provisions of 240.4(B) do not apply. It was probably 10 cycles ago when that change was made.

I don't see it at a issue that I want to put a PI in on.