Ampacity adjustment question

[Dsg319]

Thanks

 

[Dsg319]

It's the lesser of 10' or 10% of the adjoining length.

So no, not 20' in your example.

And if it's 100' total, then it would be 9', which is 10% of the adjoining 91'.

Cheers, Wayne

Sorry if not relevant but had a scenario come up In my mind. So if I have branch circuits in a home with none being over a hundred feet, Am I still allowed to use the 10ft sleeve and bundle or can only use 10% of the length of circuit conductor?

 

[Carultch]

Sorry if not relevant but had a scenario come up In my mind. So if I have branch circuits in a home with none being over a hundred feet, Am I still allowed to use the 10ft sleeve and bundle or can only use 10% of the length of circuit conductor?

It's 10 ft, or 10% of the remaining length, whichever is less. And if it is 2 ft or less, bundling adjustments need not apply, no matter how long the circuit is, because a different rule excepts the derate requirements.

So if the full length is the following, then up to the following lengths are allowed to have their elevated ampacity ignored.
If the full length is 22ft or less, then it is up to 2ft.
If the full length is 55ft, then it is up to 5ft. 5 ft is 10% of the remaining 50 ft.
If the full length is 99ft, then it is up to 9ft. 9 ft is 10% of the remaining 90 ft.
If the full length is 110 ft, then it is up to 10 ft. This is the overlap where 10 ft coincides with 10%.
If the full length is 220 ft, then it is up to 10 ft. After 10ft is 10%, 10 ft is the limit.

 

[Dsg319]

It's 10 ft, or 10% of the remaining length, whichever is less. And if it is 2 ft or less, bundling adjustments need not apply, no matter how long the circuit is, because a different rule excepts the derate requirements.

So if the full length is the following, then up to the following lengths are allowed to have their elevated ampacity ignored.
If the full length is 22ft or less, then it is up to 2ft.
If the full length is 55ft, then it is up to 5ft. 5 ft is 10% of the remaining 50 ft.
If the full length is 99ft, then it is up to 9ft. 9 ft is 10% of the remaining 90 ft.
If the full length is 110 ft, then it is up to 10 ft. This is the overlap where 10 ft coincides with 10%.
If the full length is 220 ft, then it is up to 10 ft. After 10ft is 10%, 10 ft is the limit.

Thank you.

 

[don_resqcapt19]

It's 10 ft, or 10% of the remaining length, whichever is less. And if it is 2 ft or less, bundling adjustments need not apply, no matter how long the circuit is, because a different rule excepts the derate requirements.
...

The language in the exception does not say that.

Exception:
Where different ampacities 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]

The language in the exception does not say that.

Ah, that's a 2017 change to 310.15(A)(2) Exception. I guess Carultch and I were out of date. : - )

They've also changed the allowance to 10 ft of the total circuit. The previous language would have allowed "10' lower ampacity - 200' higher ampacity - 10' lower ampacity" to use the exception on each 10' section separately. [And for an aggressive interpretation, the middle segment could have been only 100', not 200'.]

Cheers, Wayne

 

[wwhitney]

P.S. How does the current language preclude randomly sticking a short length of #12 Cu into any circuit, as long its under 10% and 10ft? Seems like it should say "Where different ampacities apply to portions of a circuit with identical conductor size," or something like that.

Cheers, Wayne

 

[Carultch]

P.S. How does the current language preclude randomly sticking a short length of #12 Cu into any circuit, as long its under 10% and 10ft? Seems like it should say "Where different ampacities apply to portions of a circuit with identical conductor size," or something like that.

Cheers, Wayne

Seems like going out of your way to make the circuit more complicated based on a questionable loophole, for little (if any) advantage, and another component to fail with the splice. It would also require a box to place the splice, that you otherwise wouldn't need. I agree that this should only apply to an identical conductor in both size and insulation.

 

[WasGSOHM]

A better way to state that, is that if the termination ampacity is less than the corrected and adjusted conductor ampacity, the termination ampacity governs the ampacity of the circuit.

Think of it like a chain on hooks. The chain has a strength, and the hooks have a strength. The strength of the assembly is the weaker of the two strengths. You can put a stronger chain on the hooks, but you can't take credit for its strength being greater than the strength of the hooks, when determining what load it can support.

IF you had programming THEN you might call it a bunch of IF-THEN statements.

IF (you have version xxx of the NEC AND your gauge is 12 AND there are less than N conductors) THEN (you might be right)!

And if you nest them, it's like nested parentheses.

If these NEC rules are written correctly there should be no ambiguity, but. . .

A rule:
Rugged cables should be used in hazardous environments.

What does this say about the other three cases,
rugged in benign environments,
fragile cables in hazardous,
fragile in benign.

It says nothing, believe it of not. Common sense helps you with fragile in hazardous.

Maybe that's the problem: your common sense may not be mine.

 

[shortcircuit2]

There are other ampacity correction factors to consider where calculating ampacity for a wire. You must also consider the "ambient" temperature for the location of the circuit. Another may be a raceway restriction such as LFMC used in a wet location your limited to 60 degrees default per UL. If you connect to equipment not marked with termination temperature, your limited to 60 degrees default.

LFNC has similar 60-degree C (140 F) limitation in wet location use. I also stumbled upon a restriction for LFNC in 356.12(2) where it can not be used where the combination of ambient and conductor temperature is in excess of which LFNC is listed. So if LNFC is used in a 90-degree F environment, you only can heat those conductors to 50-degrees F? Seems to make the product not useable.

 

[Carultch]

They've also changed the allowance to 10 ft of the total circuit. The previous language would have allowed "10' lower ampacity - 200' higher ampacity - 10' lower ampacity" to use the exception on each 10' section separately. [And for an aggressive interpretation, the middle segment could have been only 100', not 200'.]

I stand corrected on my 2014 knowledge of this rule. Thanks to the rooftop adder being greatly reduced in 2017, I haven't had to use this rule where 2017 or 2020 applies.

Still leaves open the possibility of:
5 ft lower ampacity : 200 ft higher ampacity : 5 ft lower ampacity. Two installments of this exception, as long as they add up to 10 ft, or 10% of the total length.