Current carrying conductors?

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ramsy said:
Denis Alwon points out 240.4(D) prohibits the 75°C operating column for these small conductors.
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That's not true if the terminals on both ends are rated for 75° C and the conductor is at least a 75° C conductor.
 
kwired said:
I see no mentioning of temperature at all in 240.4(D).
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240.4(D) operating ampacity limits refer to the 60°C column of Chap. 3 Tables.
240.4(D) prohibits the 75°C operating ampacity of Table 310.15(B)(16).

We intuitively fail 240.4(D) when selecting the 75°C operating temperature column from Chap. 3 idiot tables.

Qualified electricians trained under NFPA-70, while perhaps aware of 110.14(C), 220.18, or 334.80, must use NFPA idiot Tables with the concept of temperature out of sight, and out of mind, expected to memorize numbers from 240.4(D) (indirectly referencing temperature columns), critically over-riding the idiot tables, as do common-inductive equipment, and listings limits burried elsewhere in this code.

When using NFPA-70 Chap. 3 idiot tables without knowing temperature, all idiotic rules are critical to get it right.

Apparently nobody is getting it, or following the 60°C limits referenced in 240.4(D), critical to getting Chap. 3 tables right.
 
infinity said:
That's not true if the terminals on both ends are rated for 75° C and the conductor is at least a 75° C conductor.
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Without qualified engineering supervision the limits of 2420.4(D) have always applied to all of us.

Chap 3 idiot table are subject to, over-ridden by 240.4(D), 110.14(C), 220.18, or 334.80, etc..

Using NFPA-70 Chap. 3 idiot tables is more problematic and difficult than the engineering it tries to replace.
 
240.4(D) does not mention temperature rating of insulation at all. It is simply an additional limitation imposed on top of the usual ampacity procedure.

NM-B cable has 90C rated conductor insulation, and the 90C ampacity may be used as the starting point for ampacity calculations, with the final ampacity further limited to (a) the tabular (unadjusted) 60C ampacity and (b) any limitations imposed by 240.4(D).

Cheers, Wayne
 
ramsy said:
Without qualified engineering supervision the limits of 2420.4(D) have always applied to all of us.

Chap 3 idiot table are subject to, over-ridden by 240.4(D), 110.14(C), 220.18, or 334.80, etc..

Using NFPA-70 Chap. 3 idiot tables is more problematic and difficult than the engineering it tries to replace.
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I cannot follow your posts but I will say that my last statement was correct.
 
wwhitney said:
..with the final ampacity further limited to (a) the tabular (unadjusted) 60C ampacity and (b) any limitations imposed by 240.4(D).
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I doubt inspectors are wise to 240.4(D) limitations, much less all other limits with the derateing or adjustment process in Chap. 3.

My guess is Inspectors rely on plans, from architects, or municipal building department Plan Checks, both using qualified engineering expert systems that are not required to consider 240.4(D).
 
ramsy said:
I doubt inspectors are wise to 240.4(D) limitations, much less all other limits with the derateing or adjustment process in Chap. 3.

My guess is Inspectors rely on plans, from architects, or municipal building department Plan Checks, both using qualified engineering expert systems that are not required to consider 240.4(D).
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Are you saying that you cannot use a 75° C conductor with 75° C terminals at the conductors 75° C ampacity?
 
It doesn't have to do with temp. What I was getting at was that the 75C is not viable for 14, 12 and 10 because the wire overcurrent protective device cannot be higher than what the 60C column states except for where 240.4(G) allows. The op wanted to use a 35 amp overcurrent protective device for #10. You cannot do that
 
Dennis Alwon said:
It doesn't have to do with temp. What I was getting at was that the 75C is not viable for 14, 12 and 10 because the wire overcurrent protective device cannot be higher than what the 60C column states except for where 240.4(G) allows. The op wanted to use a 35 amp overcurrent protective device for #10. You cannot do that
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#10 THHN is good for 35 amps at 75° C so if the wiring method, terminals, and 240.4(G) allows it you can use #10 at 35 amps.
 
Dennis wins!
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Dennis pointed out to 240.4(D) to me.

I believe the NFPA-70 derating and adjustment process in Chap. 3 should point out 240.4(D) to everybody, and the exceptions in 240.4(E) & (G), which is the most comprehensive list of issues that break Chap. 3 ampacity tables.

Chap. 310.1 only mentions a limited scope with its warning about motor loads.

310.15 section (C) Engineering Supervision, does show the preferred method of Architects and Planning departments, as the only alternative to these problematic idiot tables.

I would rather pay for an ampacity calculator designed under qualified engineering supervision, than waist any more aggravation trying to explain NFPA idiot tables and all the exceptions.
 
ramsy said:
I believe the NFPA-70 derating and adjustment process in Chap. 3 should point out 240.4(D) to everybody, and the exceptions in 240.4(E) & (G), which is the most comprehensive list of issues that break Chap. 3 ampacity tables.
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It actually does. Look at the double asterisks by sizes 18 through 10 in Table 310.15(B)(16), and the ** note at the bottom.
 
LarryFine said:
It actually does. Look at the double asterisks by sizes 18 through 10 in Table 310.15(B)(16), and the ** note at the bottom.
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NFPA's idiot Table derating, adjustments, and load-calculations avoid IEEE formulas, in favor of private copywrite of public comments.

Equipment listed in 240.4(G) like Motors require exceptions and separate adjustments beyond Chap.3 Tables for all sizes, not just small conductors => #10.

Apparently the Asterix are not working, since they are incomplete, prompting detrimental reliance on impossible Table schemes that fail separate adjustments or exceptions for all systems listed in 240.4(G), for all wire sizes.
 
ramsy said:
NFPA's idiot Table derating, adjustments, and load-calculations avoid IEEE formulas, in favor of private copywrite of public comments.

Equipment listed in 240.4(G) like Motors require exceptions and separate adjustments beyond Chap.3 Tables for all sizes, not just small conductors => #10.

Apparently the Asterix are not working, since they are incomplete, prompting detrimental reliance on impossible Table schemes that fail separate adjustments or exceptions for all systems listed in 240.4(G), for all wire sizes.
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240.4(D) is a maximum overcurrent protection rule (general use rule, with some exceptions like motors that has been mentioned). It has little to nothing to do with conductor ampacity selection and adjustments. If you have nine 12 AWG THHN in raceway for general use circuits you can make ampacity selection and corrections/adjustments starting with 90C ampacity table. You then can not have smaller conductor than required for 75C terminal, if you have 75C terminals. When that is all said and done you still can not protect it at more than 20 amps in accordance with 240.4(D)(4).
If you should need more than 20 amp overcurrent protection then you need a larger conductor (again for general purpose applications, some specific applications mentioned in (G) may allow higher OCPD.
 
kwired said:
240.4(D) is a maximum overcurrent protection rule (general use rule, with some exceptions like motors that has been mentioned). It has little to nothing to do with conductor ampacity selection and adjustments. If you have nine 12 AWG THHN in raceway for general use circuits you can make ampacity selection and corrections/adjustments starting with 90C ampacity table. You then can not have smaller conductor than required for 75C terminal, if you have 75C terminals. When that is all said and done you still can not protect it at more than 20 amps in accordance with 240.4(D)(4).
If you should need more than 20 amp overcurrent protection then you need a larger conductor (again for general purpose applications, some specific applications mentioned in (G) may allow higher OCPD.
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Well done. Now what happens when the load is LED lights?

Lighting and retrofits demand the same load calculation across industrial electrical, construction, electrical maintenance, and service industries, and they all are getting it wrong.
 
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