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Thread: Oops!

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    Default Oops!

    Sparky strike again today in Frisco pre-drywall inspection.

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    Default Re: Oops!

    Hey, the electrician KNEW he would not be allowed to cut a hole that large through those members, so he figured a way around that problem ...

    However, there are some here who still do not understand and comprehend "lack of maintaining spacing" for NM cables, I wonder what those people think of that large group of "lack of maintaining spacing" cables and if the consider that as such, and do they consider that as being greater than 24", and would that require derating like the NEC says it requires.

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    Default Re: Oops!

    Quote Originally Posted by Jerry Peck View Post
    Hey, the electrician KNEW he would not be allowed to cut a hole that large through those members, so he figured a way around that problem ...

    However, there are some here who still do not understand and comprehend "lack of maintaining spacing" for NM cables, I wonder what those people think of that large group of "lack of maintaining spacing" cables and if the consider that as such, and do they consider that as being greater than 24", and would that require derating like the NEC says it requires.
    JP: I told them to either relocate the cables or install them in conduit and to separate the cables that are bundled or de-rate the circuits. That drew smiles all around.

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    Default Re: Oops!

    I am going to assume nobody is dumb enough to just do that without having negotiated it w/ the builder or owner. Sparky is a part of my resume and any association to work like that is too painful to acknowledge. Maybe that area will be soffited ? Looks like the sandwiched layers of engineered lumber were too much for sparky to drill. Probably didn't have a hole hawg, ( right angle drill motor ). It is no justification, but those I beam webs are often manufactured w/ knock-outs and it is unlikely that those KOs would be lined up through that many layers. That just could not have been done by an electrician. Probably an engineer from Maine or similar


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    Default Re: Oops!

    Quote Originally Posted by Garry Blankenship View Post
    I am going to assume nobody is dumb enough to just do that without having negotiated it w/ the builder or owner. Sparky is a part of my resume and any association to work like that is too painful to acknowledge. Maybe that area will be soffited ? Looks like the sandwiched layers of engineered lumber were too much for sparky to drill. Probably didn't have a hole hawg, ( right angle drill motor ). It is no justification, but those I beam webs are often manufactured w/ knock-outs and it is unlikely that those KOs would be lined up through that many layers. That just could not have been done by an electrician. Probably an engineer from Maine or similar
    You assume too much. The plans were on site. There is not soffit in the plans. It was a licensed electricista.

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    Default Re: Oops!

    Quote Originally Posted by Aaron Miller View Post
    JP: I told them to either relocate the cables or install them in conduit and to separate the cables that are bundled or de-rate the circuits. That drew smiles all around.
    @Aaron. So after the smiles dissipated, did they give any indication as to how this will be remedied?

    @Jerry. The 24" you mention, does that mean that cables can be bundled <= @24", so to pass through something, and then must separate? What is a standard separation?

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    Quote Originally Posted by Steven Turetsky View Post
    The 24" you mention, does that mean that cables can be bundled <= @24", so to pass through something, and then must separate? What is a standard separation?
    Yes, the NM cables can be located such that "lack of maintaining spacing" (the code no longer uses the term "bundled" as that created confusion as to what a "bundle" was or was not) can continue for up to 24 inches (one such use would be to pass through multiple holes in those joists - as long as no insulation is installed around the cables where they pass through the holes), then the cables are separated.

    Now comes the not-specified-in-the-code part of the answer: While the intent of the code is to have the NM cables separated for ventilation to dissipate heat and to only allow short distances of "lack of maintaining spacing" where heat could build up, the code wording actually allows just the opposite - one could install the cables in lengths of up to 24" with "lack of maintaining spacing", separate the cables, and then go back to "lack of maintaining spacing" for up to another 24", separate the cables and then go back to ... and keep repeating the cycle. While that actually does meet the actual wording of code, it is not the intent of the code to allow that.

    Here is another not-specified-in-the-code part of the answer: The distance between the cables to be considered as 'maintaining spacing' is not specified. Many years ago I called Southwire®, the makers of Romex™, and talked with their engineers about what "maintaining spacing" meant to them. They said they had never been asked that before, but ... their first response was 'Well, if you used staples to secure the cables and there were two cables side by side, and you placed the staples next to each other, the cables would be about 1/4" apart' ... then after some further discussion, one of the engineers said 'If we go by what is stated, maintaining spacing, then we need to start where the spacing which is to be maintained starts, at the boxes and the spacing between where the NM cables enter' ... further discussion went into 'two cables are allowed in a typical fitting, so what is the spacing of those which needs to be maintained' ... the responses were 'back to the two staples securing two cables side by side, or about 1/4" would be the minimum' ...

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    Default Re: Oops!

    Quote Originally Posted by Steven Turetsky View Post
    @Aaron. So after the smiles dissipated, did they give any indication as to how this will be remedied?

    @Jerry. The 24" you mention, does that mean that cables can be bundled <= @24", so to pass through something, and then must separate? What is a standard separation?
    Time for some fact unsubstantiated opining. I've always felt the heat build-up concern w/ bundling is more directly associated with individual conductors in raceways than cable assemblys in open air. This is not born out in code language, but type NM cable, ( for example ), has two insulating and space creating layers that single conductors do not. A conduit inhibits or at least slows heat dissapation. Further; cable assemblys like NM contain complete circuits, hots with their associated neutrals and grounds which enables better heat or hysterisis dissapation. Conduits also will have complete circuits, but it is possible for same phase conductors to be shouldered together in a conduit where that is not possible with N/M. I have never seen bundling called on a N/M job other than at the panel entrance. I know it can be and it is called, but with cable assemblys I see no reason for calling it. I'd love to see a N/M installation study report that bears out this phantom heat build-up, but doubt anyone could find one.


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    Default Re: Oops!

    Quote Originally Posted by Garry Blankenship View Post
    I have never seen bundling called on a N/M job other than at the panel entrance. I know it can be and it is called, but with cable assemblys I see no reason for calling it.
    I guess you are from areas which do not have thorough inspectors?

    In South Florida where I was, it was called out frequently, and I call it out frequently.

    I'd love to see a N/M installation study report that bears out this phantom heat build-up, but doubt anyone could find one.
    Go ask the people who have begun to make the code address "lack of maintaining spacing', especially with NM cables, more stringent, and they do not make these code changes without having substantiation provided with the proposal for the code change - if the proposer does not provide sufficient substantiation, then the code change is not approved, it may be sent back with a request for more data and substantiation.

    By the way, as I pointed out in my previous post, "bundling" is not longer addressed in the code, it is "lack of maintaining spacing".

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    Default Re: Oops!

    Quote Originally Posted by Jerry Peck View Post
    I guess you are from areas which do not have thorough inspectors?
    I am from an area where the inspectors amazingly enough are more realistic than those who waste peoples time making them space cables in a residential* application. Yea yea I know it says somewhere that you and many of the other unrealistic inspectors can cite at a seconds notice that spacing is required and yea yea I know some ignorant group of no experience brainless morons with an agenda passed that BS into code and yea yea I know this sentence is running on and on. But guess what, neither I nor any inspector I have ever met has cited or been cited for bundling of cables except when they are bundled in a conduit!

    *Above rant does not apply to commercial or industrial applications!


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    Quote Originally Posted by Lou Romano View Post
    I am from an area where the inspectors amazingly enough are more realistic than those who waste peoples time making them space cables in a residential* application.
    So you think it is unrealistic and a waste of time to have electricians do what they should already know what to do and to help reduce the risk of fires?

    Check, got it, now I know where you are coming from.

    *Above rant does not apply to commercial or industrial applications!
    Oh, so you treat residential dwellings, where people live and sleep, as minor irritations and safety is not important?

    Check, got it, understand where you are coming from now.

    Just additional evidence to go along with your other posts letting us know was you stand with regard to property damage and life safety for residential dwellings.

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    Default Re: Oops!

    All you and other people who think like you do is escalate the cost of building a house without reasonable cause. Name one house that burned down or even caught fire because of "bundled" cables... just one! You can't because it has NEVER happened and if it did it was because of a staple pinching a cable not the bundle itself!

    I am sick and tired of people who want nothing more than to complicate simple things. I haven't posted here in a while because every post I read is filled with a bunch of inane banter from people who have no experience except for maybe what they have read in some book or worse yet...learned here!

    Don't bother ignoring me, I won't be back!


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    Default Re: Oops!

    Quote Originally Posted by Jerry Peck View Post
    So you think it is unrealistic and a waste of time to have electricians do what they should already know what to do and to help reduce the risk of fires?

    Check, got it, now I know where you are coming from.



    Oh, so you treat residential dwellings, where people live and sleep, as minor irritations and safety is not important?

    Check, got it, understand where you are coming from now.

    Just additional evidence to go along with your other posts letting us know was you stand with regard to property damage and life safety for residential dwellings.
    The loads are not the same in a residential occupancy as the loads in a non-resi building, the NEC requirements need to be modified for dwellings as it's a non-issue, if it was a problem, there would be a whole heap more house fires.

    The NEC has become a sales tool, the manufacturers sold a bill of goods w/ AFCI's, bubble covers are a PITA unless the best quality is used,(which is not happening in low bid contruction) making them more of a hazard when the lids get broken off leaving the receptacle exposed to the weather, & a lot of people will not give a rats behind about the damage and just leave it as-is.


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    Quote Originally Posted by Rollie Meyers View Post
    The loads are not the same in a residential occupancy as the loads in a non-resi building, the NEC requirements need to be modified for dwellings as it's a non-issue, if it was a problem, there would be a whole heap more house fires.
    The tests they have done have been on wood frame dwelling type structures. If you and Lou decide not to pay attention to what the NFPA finds and the changes in the NEC, there is nothing I or anyone can do to make you do the work correctly until your local inspector catches up to speed.

    The NEC has become a sales tool, the manufacturers sold a bill of goods w/ AFCI's, bubble covers are a PITA unless the best quality is used,(which is not happening in low bid contruction) making them more of a hazard when the lids get broken off leaving the receptacle exposed to the weather, & a lot of people will not give a rats behind about the damage and just leave it as-is.
    Maybe at some point in time some attorney will see these postings and say: 'That is how electricians feel about this stuff? Ummm, maybe I can get their attention by adding their names to the list of Defendants on this case I have where seven family members died in a house fire traced back to the electrical system.'. Maybe someday we will get to meet ...

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    Quote Originally Posted by Garry Blankenship View Post
    I am going to assume nobody is dumb enough to just do that without having negotiated it w/ the builder or owner. Sparky is a part of my resume and any association to work like that is too painful to acknowledge. Maybe that area will be soffited ? Looks like the sandwiched layers of engineered lumber were too much for sparky to drill. Probably didn't have a hole hawg, ( right angle drill motor ). It is no justification, but those I beam webs are often manufactured w/ knock-outs and it is unlikely that those KOs would be lined up through that many layers. That just could not have been done by an electrician. Probably an engineer from Maine or similar
    Three of those four members are glue lams, not I joists. While glue lams can be drilled with limitations, most builders do not want them drilled at all.


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    Quote Originally Posted by Jerry Peck View Post
    The tests they have done have been on wood frame dwelling type structures. If you and Lou decide not to pay attention to what the NFPA finds and the changes in the NEC, there is nothing I or anyone can do to make you do the work correctly until your local inspector catches up to speed.



    Maybe at some point in time some attorney will see these postings and say: 'That is how electricians feel about this stuff? Ummm, maybe I can get their attention by adding their names to the list of Defendants on this case I have where seven family members died in a house fire traced back to the electrical system.'. Maybe someday we will get to meet ...

    Who said anything about not installing code required items? I am waiting for the time when AFCI's fail to do what was claimed they will do, when a slimey lawyer gets into a case where there is loss of life or serious injury because of the bill of goods that was sold to the code panel(s), BTW if GFCI's had been required everywhere, I would be very comfortable w/ it, as they are cheap & reliable. That being said, I install AFCI's,& in use (bubble) covers, & I do not care for bundling homeruns..... Lab tests do not replicate real world conditions, like EPA fuel mileage, or crash test data for a couple of examples.


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    Default Re: Oops!

    Quote Originally Posted by Robert Meier View Post
    There is a provision int the NEC to allow bundling of NM cable more than 24" without the requirement to apply derating factors. {310.15(A)(2)Ex}This is one reason why installations like the one in the photo may not require derating.
    310.15(A)(2) Selection of Ampacity. Where more than one ampacity
    applies for a given circuit length, the lowest value shall be
    used.
    Exception: Where two different ampacities apply to adjacent
    portions of a circuit, the higher ampacity shall be permitted to
    be used beyond the point of transition, a distance equal to 3.0
    m (10 ft) or 10 percent of the circuit length figured at the
    higher ampacity, whichever is less
    Robert,

    I have not seen an installation in a dwelling unit (residence) to which that is applicable as the "circuit ampacity" is the same from the overcurrent protection to the furthest end of the circuit unless there is another, lower rated, overcurrent device taped off it. Example: a 20 amp breaker feeds a #12 AWG circuit which feeds lights and receptacles. The "circuit ampacity" is 20 amps from the breaker to the end of the circuit.

    And the complaint is in applying this to dwelling units, not to other-than-dwelling units ("commercial" is not a good term to use for other-than-dwelling units).

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    Quote Originally Posted by Robert Meier View Post
    Are you saying that you disagree that 310.15(A)(2)Ex. would apply to bundled NM cable? The purpose of the exception is to allow the heat sink effect of the other portion of the circuit to keep the conductors within their safe operating range.
    I am saying that you are reading it wrong, not that I am disagreeing with it.

    You must keep in mind what it is referring to: "Where two different ampacities apply to adjacent portions of a circuit,", and there is BUT ONE ampacity of that circuit.

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    Don't bother ignoring me, I won't be back!
    We certainly hope that is the case.

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    Default Re: Oops!

    Quote Originally Posted by Jerry Peck View Post
    I guess you are from areas which do not have thorough inspectors?

    In South Florida where I was, it was called out frequently, and I call it out frequently.



    Go ask the people who have begun to make the code address "lack of maintaining spacing', especially with NM cables, more stringent, and they do not make these code changes without having substantiation provided with the proposal for the code change - if the proposer does not provide sufficient substantiation, then the code change is not approved, it may be sent back with a request for more data and substantiation.

    By the way, as I pointed out in my previous post, "bundling" is not longer addressed in the code, it is "lack of maintaining spacing".
    What people ? Who are they and what data do they have to support this. people say and it is well known does not cut it. What heat build up ? I just want to see the data. I think the code is an effective medium, but I do not think it is either perfect or beyond monetary influence. Show me the meat !


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    Quote Originally Posted by Garry Blankenship View Post
    What people ? Who are they and what data do they have to support this. people say and it is well known does not cut it. What heat build up ? I just want to see the data. I think the code is an effective medium, but I do not think it is either perfect or beyond monetary influence. Show me the meat !
    Whether the code is perfect or not is not the issue. Once adopted by a municipality it becomes the law; like it or not.

    Now, get your fork and steak knife . . .

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    Quote Originally Posted by Aaron Miller View Post
    Whether the code is perfect or not is not the issue. Once adopted by a municipality it becomes the law; like it or not.

    Now, get your fork and steak knife . . .

    http://www.copper.org/applications/e...ion_report.pdf
    Very interesting, but couldn't you at least have included some A1 Sauce?

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    Default Re: Oops!

    Quote Originally Posted by Robert Meier View Post
    Jerry I have to disagree that I'm reading it wrong, maybe we're missing something in translation.

    Here's a graphic that more clearly depicts what I'm saying regarding the application of 310.15(A)(2)Ex. The exception allows me to not consider derating on the entire circuit if a portion of the circuit fits the parameters of the 10' or 10% rule.

    Robert,

    Mike Holt's drawing would not relate to those circuits as the ampacity of the last part of the circuit which goes to a receptacle *could* still have a hair dryer, portable heater, etc., plugged into it.

    Mike Holt's drawing would only work when the ampacity of the remainder of the circuit was known. That drawing would also not apply to any of the other NM cables.

    Mike's drawing would be applicable only when the ampacity of the end of the circuit is known, and, as I said in previous posts:
    Quote Originally Posted by Jerry Peck
    I have not seen an installation in a dwelling unit (residence) to which that is applicable as the "circuit ampacity" is the same from the overcurrent protection to the furthest end of the circuit unless there is another, lower rated, overcurrent device taped off it. Example: a 20 amp breaker feeds a #12 AWG circuit which feeds lights and receptacles. The "circuit ampacity" is 20 amps from the breaker to the end of the circuit.

    And the complaint is in applying this to dwelling units, not to other-than-dwelling units ("commercial" is not a good term to use for other-than-dwelling units).
    I agree that there may be, in a non-residential installation, rare cases when that might be applicable as shown in Mike's drawing, and, where the installation of the conductors would be such that it would not be with other conductors of other circuits which would not fit that drawing and which would STILL require derating.

    How about if you provide a few examples of where that drawing would applicable to a circuit in a dwelling unit.

    How about if you provide a few examples of where that drawing would be applicable to a circuit in a non-residential installation - this should be easier, but in doing so you will probably understand why it would not be applicable to any typical residential circuit.

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    Default Re: Oops!

    Quote Originally Posted by Aaron Miller View Post
    Whether the code is perfect or not is not the issue. Once adopted by a municipality it becomes the law; like it or not.

    Now, get your fork and steak knife . . .

    http://www.copper.org/applications/e...ion_report.pdf
    Good stuff Aaron. That is the meat I was looking for. I'm both impressed and thankful that you found it. I am now a believer - - - more of a believer. The danger zone assumed some fairly unlikey circumstances, but not impossible circumstances, so I ate it and the taste wasn't so bad. Please recall that I started this with some "fact unsubstantiated opining", not assuming the code was wrong. I am surprized that bundled N/M can generate the heat indicated, even under unlikely circumstances. Thanks for the education. A tip of the hat.


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    Here is another not-specified-in-the-code part of the answer: The distance between the cables to be considered as 'maintaining spacing' is not specified. Many years ago I called Southwire®, the makers of Romex™, and talked with their engineers about what "maintaining spacing" meant to them. They said they had never been asked that before, but ... their first response was 'Well, if you used staples to secure the cables and there were two cables side by side, and you placed the staples next to each other, the cables would be about 1/4" apart' ... then after some further discussion, one of the engineers said 'If we go by what is stated, maintaining spacing, then we need to start where the spacing which is to be maintained starts, at the boxes and the spacing between where the NM cables enter' ... further discussion went into 'two cables are allowed in a typical fitting, so what is the spacing of those which needs to be maintained' ... the responses were 'back to the two staples securing two cables side by side, or about 1/4" would be the minimum' ...
    This is only an opinion and would need to be interpreted by the NFPA to be enforceable.

    All answers based on unamended National Electrical codes.

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    Default Re: Oops!

    Quote Originally Posted by Jim Port View Post
    This is only an opinion and would need to be interpreted by the NFPA to be enforceable.
    Correct ... the opinion of the manufacturer and their engineers.

    Without some other "authoritative" opinion to the contrary, that is all anyone has to go by.

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    Default Re: Oops!

    The power of the sun is formidable, but I'm struggling to see why it would be much of a concern. I'm admittedly biased in that sun is a limited commodity in my hood. Also not envisioning applications where bundled N/M would be outside. There is a U/V rated N/M cable for this, ( also direct bury rated ). Rarely saw it, but definitely different composition because it is a _itch to strip.


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    Default Re: Oops!

    Quote Originally Posted by Robert Meier View Post
    Jerry ,

    You've lost me.

    If the graphic depicted NM cables, 5' of which were bundled together and 55' that had maintained spacing between them then you would not need to apply any derating to the circuit at all. That's why the graphic shows one portion of the circuit with an ampacity of 30 amps and the other portion with an ampacity of 15 amps but the over all circuit ampacity of 30 amps. Not sure why a load would have anything to do with the application of 310.15(A)(2)Exception.
    "You've lost me. "

    "Not sure why a load would have anything to do with the application of 310.15(A)(2)Exception"

    I can see that in the above two statements.

    The application of the exception is based around the ampacity required for the load. In the example below from the Handbook, the load is known; however, in a residential installation the load is not known and is presumed to be fully loaded as the load is whatever is plugged into the receptacle. The load matters in determining the ampacity required. The exception is not to get around the derating required in 310.15(B)(2), the exception is to address the derating based on ambient temperatures as taken from Table 310.16.

    - 310.15 Ampacities for Conductors Rated 0–2000 Volts.
    - - (A) General.
    - - - (1) Tables or Engineering Supervision. Ampacities for conductors shall be permitted to be determined by tables as provided in 310.15(B) or under engineering supervision, as provided in 310.15(C).
    - - - - FPN No. 1: Ampacities provided by this section do not take voltage drop into consideration. See 210.19(A), FPN No. 4, for branch circuits and 215.2(A), FPN No. 2, for feeders.
    - - - - FPN No. 2: For the allowable ampacities of Type MTW wire, see Table 13.5.1 in NFPA 79-2007, Electrical Standard for Industrial Machinery.
    - - - (2) Selection of Ampacity. Where more than one calculated or tabulated ampacity could apply for a given circuit length, the lowest value shall be used.
    - - - - Exception: Where two different ampacities apply to adjacent portions of a circuit, the higher ampacity shall be permitted to be used beyond the point of transition, a distance equal to 3.0 m (10 ft) or 10 percent of the circuit length figured at the higher ampacity, whichever is less.

    "(2) Selection of Ampacity. Where more than one calculated or tabulated ampacity could apply for a given circuit length, the lowest value shall be used."

    The calculated ampacity may be calculated "as provided in 310.15(C)", the tabulated ampacity would be taken from Table 310.16.

    310.15(C) Engineering Supervision. Under engineering supervision, conductor ampacities shall be permitted to be calculated by means of the following general formula: (code gives formula which includes ambient temperature)

    From the 2008 NEC Handbook:
    - Application Example
    - - Three 500-kcmil THW conductors in a rigid conduit run from a motor control center for 12 ft past a heat-treating furnace to a pump located 150 ft past the motor control center. Where run in a 78°F to 86°F ambient temperature, the conductors have an ampacity of 380 amperes, per Table 310.16. The ambient temperature neat the furnace, where the conduit is run, is fond to be 113°F, and the length of this particular part of the run is greater than 10 ft and more than 10 percent of the total length of the run at the 78°F to 86°F ambient. Determine the ampacity of total run in accordance with 310.15(A)(2).
    - - Solution
    - - - In accordance with the correction factors for temperature at the bottom of Table 310.16, the ampacity is 0.82 x 380 amperes, or 311.6 amperes. This, therefore, is the ampacity of the total run, in accordance with 310.15(A)(2).
    - - - Had the run near the furnace at the 113°F ambient been 10 ft or less in length, the ampacity of the entire run would have been 380 amperes, in accordance with the exception to 310.15(A)(2). The heat-sinking effect of the run at the lower ambient temperature would have been sufficient to reduce the temperature of the conductor near the furnace.

    When derating for 310.15(B)(2), the derating is not for ambient temperature, the derating is for not allowing adequate spacing between cables/conductors to ventilate the heat.

    When you derate the conductors, first you derate for ambient, then for lack of maintaining spacing.

    The drawing example you posted shows a 12 AWG with an ampacity of 30 amps, that is not the ampacity of the circuit, that is the ampacity the conductor is derated from, and for a 12 AWG to have a 30 amp ampacity the insulation would be 90°C (194°F), THHN/THHW/THWN/etc.

    So let's start with the example drawing you posted (after all, you are asking me about the drawing you posted):
    - Let's take a 20 amp bathroom circuit of 12 AWG NM-B with a circuit ampacity of 30 amps for derating purposes and which has an 60 foot run, that run goes up into an attic and then goes 30 feet across an attic, the attic can get to 135°F in the summer, then back down into a wall to the bathroom. The 30 feet across the attic far exceeds 10 feet and also far exceeds 10% of the total run.
    - The 12 AWG NM-B cable starts off with a rating of 30 amps for derating purposes, Table 310.16 shows that 90°C (194°F) insulation needs to be derated by a factor of 0.71 to 21.3 amps. That 21.3 amps is still sufficient for the 20 amp circuit it is used for ... provided no additional derating needs to be done.
    - In the case of the photo, additional derating does need to be done. There are, let's estimate this, 16 2-conductor NM cables for 32 conductors, and derating for 32 conductors is to be adjusted down to 40%. Thus the derated for ambient ampacity of 21.3 now needs to be derated to 40% to 8.52 amps. That is not even suitable to use on a 10 amp breaker, if you could even find one.

    Now let's take another example which may allow your posted exception to come into play using the same example circuit:
    - Let's take a 20 amp bathroom circuit of 12 AWG NM-B with a circuit ampacity of 30 amps for derating purposes and which has an 15 foot run, that run goes up into an attic and then goes 1 foot across an attic (in this example, the bathroom backs up to the garage wall where the panel is located so the run in the attic is basically up-and-back-down), the attic can get to 135°F in the summer, then back down into a wall to the bathroom. The 1 foot across the attic is well within the 10 feet and also well within the 10% of the total run.
    - The 12 AWG NM-B cable starts off with a rating of 30 amps for derating purposes, Table 310.16 shows that 90°C (194°F) insulation needs to be derated by a factor of 0.71 to 21.3 amps. That 21.3 amps is still sufficient for the 20 amp circuit it is used for ... provided no additional derating needs to be done ... however ... 310.15(A)(2) says that if the run is the lesser of 10 feet or 10% of the total run then the ampacity may be the larger of the two ampacity ratings, i.e., derated to 21.3 amps or 30 amps, so the ampacity for derating is still 30 amps for any additional derating.
    - In the case of the photo, additional derating does need to be done. There are, let's estimate this, 16 2-conductor NM cables for 32 conductors, and derating for 32 conductors is to be adjusted down to 40%. Thus the NOT-derated for ambient ampacity of 30 now needs to be derated to 40% to 12 amps. That is STILL not suitable to use on a 15 amp breaker.
    - To address the above, the bundle of NM cables is split into two bundles, leaving 8 NM cables (16 conductors) in each bundle; so let's derate for the additional derating again: 30 amps NOT-derated for ambient derated now needs to be derated to 50% to 15 amps. That is now suitable for a *15 amp* breaker, but this is a *20 amp* bathroom circuit.
    - So we try it again, the above two bundles are further split into 2 separate bundles of 4 NM cable (8 conductors) in each bundle; so we derate once again for lack of maintaining spacing and the 30 amps is now derated to 70% to 21 amps. BINGO! MADE IT THIS TIME! That NM cable can now be used on a 20 amp bathroom circuit.

    Did you follow through that?

    You can't just go and use things out of context, you need to apply them within their context.

    Now back to what I said:
    [quote =Jerry Peck]I agree that there may be, in a non-residential installation, rare cases when that might be applicable as shown in Mike's drawing, and, where the installation of the conductors would be such that it would not be with other conductors of other circuits which would not fit that drawing and which would STILL require derating.[/quote]

    Okay, I *DID* find a way to make that fit in with a residential installation, but, as you can see, it was not as easy as you implied.

    I even made it work where that NM cable *DID NOT* need to be separated from other conductors to make it work ... but it could not be with more than 3 additional 2-conductor NM cables to allow it to work out.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  30. #30
    Garry Blankenship's Avatar
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    Default Re: Oops!

    Quote Originally Posted by Lou Romano View Post
    Don't bother ignoring me, I won't be back!
    Scott & Billy helped me out with this and I remain a rookie in Southern communication; but Bless You


  31. #31
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    Default Re: Oops!

    Quote Originally Posted by Garry Blankenship View Post
    Scott & Billy helped me out with this and I remain a rookie in Southern communication; but Bless You

    "Bless His Heart."


    It Might have Choked Artie But it ain't gone'a choke Stymie! Our Gang " The Pooch " (1932)
    Billy J. Stephens HI Service Memphis TN.

  32. #32
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    Default Re: Oops!

    Quote Originally Posted by Robert Meier View Post
    Some other food for thought. The 2005 NEC required multiple NM cables going through firestopped holes in framing to be derated. For all intents and purposes this was unenforceable unless the conductor length was 30" or less. The 2008 corrected this be requiring that 310.15(A)Ex not apply to this type of installation.
    It was also enforceable under the 2005 NEC when read as stated, not as come presumed, and apparently that is how you presumed it also - no length was specified or required.

    This is why it *WAS* enforceable under the 2005 NEC:
    - 334.80 Ampacity.
    - - The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15. The ampacity shall be in accordance with the 60°C (140°F) conductor temperature rating. The 90°C (194°F) rating shall be permitted to be used for ampacity derating purposes, provided the final derated ampacity does not exceed that for a 60°C (140°F) rated conductor. The ampacity of Types NM, NMC, and NMS cable installed in cable tray shall be determined in accordance with 392.11.
    - - Where more than two NM cables containing two or more current-carrying conductors are bundled together and pass through wood framing that is to be fire- or draft-stopped using thermal insulation or sealing foam, the allowable ampacity of each conductor shall be adjusted in accordance with Table 310.15(B)(2)(a).

    Note that it says "in accordance with Table 310.15(B)(2)(a).", and that is *DOES NOT* say "in accordance with 310.15(B)(2)(a)."

    Did you notice the word "Table" in Table 310.15(B)(2)(a)?

    TABLE 310.15(B)(2)(a) does not mention length at all.

    The 2008 corrected this be requiring that 310.15(A)Ex not apply to this type of installation.
    It did/does? Where?

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

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