3x500 for 1200A panel

[Carultch]

What is the ambient temperature

-Jon

Usually the basic derate for ambient temperature, typically 0.96 as most US ambient temperatures are slightly above 30C, is not enough to reduce the 90C wire ampacity below the 75C terminal ampacity. And the 75C ampacity is what you start with, no adjustments or corrections for temperature, in most cases for terminations. The 90C ampacity is what you get to use for temperature correction and bundling adjustments, which is a different value limiting the wire amps.

 

[jim dungar]

I am not sure it was ever permitted. Even in the 1978 code you could only round up to the next standard sized OCPD where the OCPD was 800 amps or less, just like in the current code.

It was commonly done for transformer secondary conductors because many code users did not understand the difference between conductor ampacity and the permission in 240 to use an oversized OCPD. Even though it was commonly done, it was a violation. This was addressed in the 2005 NEC with a provision in 240.21 that said you could not use the "round-up" rule for tap conductors or transformer secondary conductors.

You are correct that over the years article 240 has probably never allowed 'protective device rounding up' above 800A. It used to be covered by an Exception, like in 1975 240.3, but now it has its own explicit section 240.6.
The provision for supervised industrial installations kind of covers the practice in 'heavy industries' where the loading managed and controlled.

 

[Sierrasparky]

Maybe they are using the 90 degree column?
Some folks thing Lugs are rated at 90

 

[Carultch]

Maybe they are using the 90 degree column?
Some folks thing Lugs are rated at 90

It's not just lugs that matter. It is lugs and equipment as a manufactured assembly. Commonly, you will see AL9CU lugs on your equipment, and still not be able to use the 90C column.

 

[don_resqcapt19]

But not under the context of the conversation. We are talking building wire.

Comments based on the 2017 National Electrical Code.

It becomes building wire when they add the RHH or RHW on the jacket. Are you saying that 310.15(C) cannot be used for building wire?

 

[MasterTheNEC]

It becomes building wire when they add the RHH or RHW on the jacket. Are you saying that 310.15(C) cannot be used for building wire?

Don I think you know very well I understand listings of wire and cable. I work in that industry. The question was on higher ampacity of the DLO being used to meet the needs of the question which was 3x 500 and why manufacturers do not push for higher ampacity of 500 kcmil and so on.

The use of dual/triple or quad ratings on wire is not the issue here. The question I was addressing was the question regarding why manufacturers do not push for higher amp values on the products we offer. No question that if it has a dual or triple rating of RHH or RHW-2 that it would be acceptable in building wiring but the ampacity in question would have to conform to that within the NEC tables already expressed.

In regards to 310.15(C) with regards to conductors rated 2001 to 35,000 volts I will not comment on as we do not manufacturer such animals and would not consider them premise wiring applications from our perspective. Now if an engineer would like to invoke 310.15(B) then they own it but since you did not state (B) I will not venture down that path. Manufacturers of building wire (which is what I thought we were talking about) will adhere to the values of 310.15(B)(16) or the other tables where applicable.

 

[jumper]

Good point. So just crank the adjustment (if it has one) on the 1200A down to 1140A?

Maybe. One would have to meet 240.6(C), restricted access or (B) would apply:

(B) Adjustable-Trip Circuit Breakers.
The rating of adjustable-trip circuit breakers having external means for
adjusting the current setting (long-time pickup setting), not
meeting the requirements of 240.6(C), shall be the maxi-
mum setting possible.

 

[don_resqcapt19]

...
In regards to 310.15(C) with regards to conductors rated 2001 to 35,000 volts I will not comment on as we do not manufacturer such animals and would not consider them premise wiring applications from our perspective. Now if an engineer would like to invoke 310.15(B) then they own it but since you did not state (B) I will not venture down that path. Manufacturers of building wire (which is what I thought we were talking about) will adhere to the values of 310.15(B)(16) or the other tables where applicable.

I see nothing is 310.15(C) that restricts its use to conductors rated 2001 to 35,000 volts.

310.15Ampacities for Conductors Rated 0–2000 Volts.
(A)General.
(1)Tables or Engineering Supervision. Ampacities for conductorsshall be permitted to be determined by tables as provided in 310.15(B) or under engineering supervision, as provided in 310.15(C).
…
](C) Engineering Supervision. Underengineering supervision, conductor ampacities shall be permitted to becalculated by means of the following general equation:[/quote]

I doubt that a calculation would take the 535 KCMIL DLO/RHW to an ampacity that would exceed 400 amps, and the calculation would have to be done based on a maximum conductor temperature of 75°C to comply with the termination rules in 110.14(C).

 

[MasterTheNEC]

Don I think you know very well I understand listings of wire and cable. I work in that industry. The question was on higher ampacity of the DLO being used to meet the needs of the question which was 3x 500 and why manufacturers do not push for higher ampacity of 500 kcmil and so on.

The use of dual/triple or quad ratings on wire is not the issue here. The question I was addressing was the question regarding why manufacturers do not push for higher amp values on the products we offer. No question that if it has a dual or triple rating of RHH or RHW-2 that it would be acceptable in building wiring but the ampacity in question would have to conform to that within the NEC tables already expressed.

In regards to 310.15(C) with regards to conductors rated 2001 to 35,000 volts I will not comment on as we do not manufacturer such animals and would not consider them premise wiring applications from our perspective. Now if an engineer would like to invoke 310.15(B) then they own it but since you did not state (B) I will not venture down that path. Manufacturers of building wire (which is what I thought we were talking about) will adhere to the values of 310.15(B)(16) or the other tables where applicable.

I actually meant 310.60(B) as it pertained to your reference to 310.15(C) and not 310.15(B) in terms of the engineer but in my mind moved on to higher voltages ..my bad and sorry. But alas since I am not able to edit it....so be it. Other wise most (not MTW and so but you get the gist) wire used within the premise will conform to 310.104(A) and ampacity values expressed in the tables under 310.15(B) and in terms of engineering supervision...thats again on them as we manufacturers want no parts in that.

 

[GoldDigger]

Maybe. One would have to meet 240.6(C), restricted access or (B) would apply:

(B) Adjustable-Trip Circuit Breakers.
The rating of adjustable-trip circuit breakers having external means for
adjusting the current setting (long-time pickup setting), not
meeting the requirements of 240.6(C), shall be the maxi-
mum setting possible.

So unless restricted access applies, wires connected to a 1200A adjustable trip breaker must have an allowed ampacity of 1200A regardless of the calculated load or the trip setting?

 

[MasterTheNEC]

I see nothing is 310.15(C) that restricts its use to conductors rated 2001 to 35,000 volts.
310.15Ampacities for Conductors [/COLOR]Rated 0–2000 Volts[/SIZE].[/FONT][/B]
(A)General.
(1)Tables or Engineering Supervision. Ampacities for conductorsshall be permitted to be determined by tables as provided in 310.15(B) or under engineering supervision, as provided in 310.15(C).
…
](C) Engineering Supervision. Underengineering supervision, conductor ampacities shall be permitted to becalculated by means of the following general equation:

I doubt that a calculation would take the 535 KCMIL DLO/RHW to an ampacity that would exceed 400 amps, and the calculation would have to be done based on a maximum conductor temperature of 75°C to comply with the termination rules in 110.14(C).

I get you....but see the engineer supervision aspect is on THEM...not the wire and cable manufacturers. I just had a case where an engineer did engineering supervision and stated an elevated ampacity of a conductor and the conductor actually failed. It was not our wire but I was called in as expert witness as an outside source and fact was the engineer took on that responsibility and that indemnified the manufacturer.

Sorry....I got my quotes screwed up....it happens.

 

[jumper]

So unless restricted access applies, wires connected to a 1200A adjustable trip breaker must have an allowed ampacity of 1200A regardless of the calculated load or the trip setting?

:happyyes:, but the provisions for restricted access are not much.

(C) Restricted Access Adjustable-Trip Circuit Break-
ers.
A circuit breaker(s) that has restricted access to the
adjusting means shall be permitted to have an ampere rat-
ing(s) that is equal to the adjusted current setting (long-time
pickup setting). Restricted access shall be defined as lo-
cated behind one of the following:
(1) Removable and sealable covers over the adjusting
means
(2) Bolted equipment enclosure doors
(3) Locked doors accessible only to qualified personnel.

 

[MasterTheNEC]

I see nothing is 310.15(C) that restricts its use to conductors rated 2001 to 35,000 volts.
310.15Ampacities for Conductors [/COLOR]Rated 0–2000 Volts[/SIZE].[/FONT][/B]
(A)General.
(1)Tables or Engineering Supervision. Ampacities for conductorsshall be permitted to be determined by tables as provided in 310.15(B) or under engineering supervision, as provided in 310.15(C).
…
](C) Engineering Supervision. Underengineering supervision, conductor ampacities shall be permitted to becalculated by means of the following general equation:

I doubt that a calculation would take the 535 KCMIL DLO/RHW to an ampacity that would exceed 400 amps, and the calculation would have to be done based on a maximum conductor temperature of 75°C to comply with the termination rules in 110.14(C).

My bad in terms of the reference...I was talking about Engineering Supervision and while at work got pulled to 310.60 and the brain fart just continued. However, the facts still remain that if they want to use Engineering Supervision most if not all wire and cable manufacturers will tell them they are on their own.

 

[MasterTheNEC]

What I would like to see if a re-evaluation of the ampacity values given in 310.15(B)(16) based on our modern day insulations. Those values in that table date back when the study was done on rubber insulation and other than rubber with limited input. The problem is i am sure none of my counterparts in the other wire and cable companies want to take on that task because it is a very long and detailed undertaking.

I can't begin to tell you the headache and detail of work that went into XHHW-2 being acceptable for 1000V rather than it's traditional UL 44 600V rating. This was a 2 year NEMA Study that concluded with testing that confirmed XHHW-2 is acceptable at 1000V BUT was steamrolled in CANENA meetings where mechanical protection was presented under the mask of Paschen's Law, with was irrelevant at 1000V and 30 mils of insulation. The focus when from what the task group had studied, which as the effects of 1000V on 600V rated insulation to a "What If" the electrician damaged the wire during installation and how to account for that poor installation.

Fact is you account for that using the UL 44 and UL 2556 standards that are already on the books. The mechanical protection is inherent in the demand for no less than 30 mils of insulation on a 14 AWG conductor, which is the test specimen. Test after test, data after data, and even UL proclaimed XHHW-2 acceptable at 1000V but one person (1) with a negative vote threw a monkey wrench in the entire 2 years of study just because they cited Canada having 45 mils on their RW90.

Moral of that story is......no one would support all the research and time it would take to change the values in 310.15(B)(16).

 

[Sierrasparky]

It's not just lugs that matter. It is lugs and equipment as a manufactured assembly. Commonly, you will see AL9CU lugs on your equipment, and still not be able to use the 90C column.

What if you terminated to a 90 lug and then switched to the larger size for termination.

 

[Smart $]

What if you terminated to a 90 lug and then switched to the larger size for termination.

That works... but you can't do it in the same enclosure. The minimum length of the larger size conductor has been debated without resolution. Some say at least 4' because of UL testing requirements...

 

[electrofelon]

That works... but you can't do it in the same enclosure. The minimum length of the larger size conductor has been debated without resolution. Some say at least 4' because of UL testing requirements...

Has the requirement that it be in a different enclosure been established with more certainty than the length?

 

[Sierrasparky]

That works... but you can't do it in the same enclosure. The minimum length of the larger size conductor has been debated without resolution. Some say at least 4' because of UL testing requirements...

Has the requirement that it be in a different enclosure been established with more certainty than the length?

weird I never heard that debate. Must have been long time ago.

 

[peter d]

What I would like to see if a re-evaluation of the ampacity values given in 310.15(B)(16) based on our modern day insulations.

I would like to see that as well. :thumbsup::happyyes:

 

[Smart $]

Has the requirement that it be in a different enclosure been established with more certainty than the length?

Yes. See page 4: http://www2.schneider-electric.com/...7/en_US/Wire Terminations 0110DB9901R2-02.pdf

weird I never heard that debate. Must have been long time ago.

TTBOMK, it has been a few years since it was tossed around on this forum.