60? vs 90? C - NMB

[Gunnar Alquist]

This one took me by surprise and I am trying to figure out exactly how to research it. I would very much appreciate some direction from some of the electrical code experts.

Old home (particularly for this area - 1872) that has been largely remodeled. It had knob & tube wiring, but has been completely replaced (as best as I can tell without opening walls & ceilings).

Their electrician has apparently stated that the NMB cable entering the box in the second pic is rated for 60? C but since it is going directly to a fixture rather than a box it should be rated for 90? C instead.

I was under the impression that most recessed fixtures got around that by providing a junction as a part of the fixture. The 60? C cable would be connected at the provided box and the fixture itself would have 90? C wiring between the box and the fixture.

At this point, I do not know when the home was rewired. Since there is both yellow and white NMB, I suspect the wiring has been done over a period of time rather than all at once. I do not believe that they are looking for me to pay for this, but it was something that took me by surprise. Unfortunately, I do not have any other images than those that I have posted.

3441734418

[Jerry Peck]

My recollection of the changes is:

White (14 AWG, 12 AWG, and 10 AWG) NM cable all used to be white (presuming that we are referring to the PVC outer jacketed NM cable used after the fabric NM cable).

That NM cable had 60?C rated insulation ... mostly ...

The new NM-B came into the NEC in the 1984 edition, before that ... the conductors were 60?C
rated ... or 75?C ... or 90?C ... getting fun, isn't?

Regular NM cable, marked as NM cable, contained 60?C rated conductors. NM cable with conductors rated for 75?C and 90?C had additional lettering designations following the "NM" marking.

That was made simple in 1984 as the construction of NM cable was changed to require all conductors in NM cable to be 90?C rated (for allowing use of the 90?C ampacity column for derating ampacity for ambient temperature and 'bundling'/lack of maintaining spacing) and "NM" became "NM-B" in 1984. The 60?C ampacity column was still used for overcurrent protection sizing.

Color coding of the outer NM sheath started in 2001 with 'white' indicated that it was 14 AWG sized conductors, 'yellow' indicated that it was 12 AWG sized conductor, and 'orange' indicated that it was 10 AWG conductor. Larger sizes, such as 8 AWG and 6 AWG had an outer sheath which was black.

Sooo ... if the NM cable was used under the 1984 NEC or later, the conductors were required to be 90?C rated conductors.

And after 2001 (suppliers were still allowed to sell 'white' NM cable which was in stock until they ran out of stock, so if someone is still getting 'white' NM cable and it is nor 14 AWG size, then it is really, really, really old stuff someone is still trying to get rid of almost 20 years after the change ... or ... or it may very well be fake stuff which 'is not real' NM cable.

back to your photos - if the outer sheath of the NM cable is yellow (12 AWG) or orange (10 AWG), then it was produced after 2001 ... which was a long time after the 1984 change to 90?C rated conductors.

The above dates (except for the 1984 date, which is from the NEC) are potentially a little flexible as I didn't find specific documentation for those dates (as I found in the 1984 NEC).

I find this interesting:

Their electrician has apparently stated that the NMB cable entering the box in the second pic is rated for 60?

Have the electrician send you a letter stating that the NMB going into that box is only rated 60?C. After receipt of that letter, with the electrician for acknowledging that the NM is in fact NM-B (or as many say 'NMB', and even more just say 'NM', but we know what it really is NM-B). Then reply that NM-B has 90?C rated conductors, that is what makes it NM-B, and NM-B came into the NEC in 1984.

He will then have to back track and explain his error in that he meant to say NM, not NM-B, which is when you reply that the outer color sheath of yellow and orange indicate that the NM cable was manufactured 2001 or later, and that makes it NM-B as ... NM became NM-B with the 1984 NEC.

Of course, there could be an explanation for that electrician's thinking - maybe the newest NEC he has is the 1981 NEC ... in which case he should retire. ;)

Just pondering ponderables.:welcome:

[Gunnar Alquist]

Thanks Jerry,

I am going to have to read that a couple of times.

Are the changes regarding the 60 C, 75 C, and 90 C found in the NEC or is it some referenced standard?

Was I correct in my presumption regarding the recessed light fixtures? That the 90 C insulated conductor requirement is addressed by the manufacturer-provided junction box that is separate from the actual lamp housing? Or is it still required to have 90 C wiring to the box?

[Jerry Peck]

Are the changes regarding the 60 C, 75 C, and 90 C found in the NEC or is it some referenced standard?

It was in my 1984 NEC. As I recall, and I can look at it again, when I looked in the 1984 NEC I didn't catch whst it said, but when I went to the 1984 NEC Handbook, which contains the code and explanations, that's when I saw it.

I'll scan thst part in when I look it up later today.

[quite]Was I correct in my presumption regarding the recessed light fixtures? That the 90 C insulated conductor requirement is addressed by the manufacturer-provided junction box that is separate from the actual lamp housing? Or is it still required to have 90 C wiring to the box?[/QUOTE]

I forgot about that part (I was tired and it was getting hard to finish what I was doing.

I'm typing on my phone, I'll look at that when I have my computer on later.

[Jerry Peck]

First things first: NM-B

The first page (file ending with 'a') at the bottom, then the second page (file ending with 'b') at the top addresses it.

I also noticed that I was incorrect with the "NM-B" as the handbook says "NMB" as the proper designation. Me bad.

[Jerry Peck]

Their electrician has apparently stated that the NMB cable entering the box in the second pic is rated for 60? C but since it is going directly to a fixture rather than a box it should be rated for 90? C instead.

I was under the impression that most recessed fixtures got around that by providing a junction as a part of the fixture. The 60? C cable would be connected at the provided box and the fixture itself would have 90? C wiring between the box and the fixture.

Fixture manufacturer's get around that 90C rating for conductors by having a separate box (you have seen many, most?, recessed fixtures with a separate box off to one side on the rough-in kit, with a separate lead going to the recessed lighting housing.

However 1 ... :cool: ... the second photo shows a box directly mounted to the top of the fixture, with that box being at the hottest area of the recessed fixture (the top of it), so that likely would require 90C rated conductors.

However 2 ... :cool: ... that yellow outer sheath NM cable is indicating to all that the conductors in the NM cable are 90C rated - this is because 90C rated conductors have been required since 1984 and the yellow outer color only began in 2001.

But ... you do see the other things in those photos, I presume.

[Gunnar Alquist]

I also noticed that I was incorrect with the "NM-B" as the handbook says "NMB" as the proper designation. Me bad.

Thank you very much for all the information Jerry. Looks like I have a bit of reading and research before me.

I have some significant holes in my Electric Code archive that I guess I am going to have to plug. You wouldn't happen to know any free-to-cheap sources for out-of-date NEC (preferrably handbooks), would you? The oldest that I have is (I believe) the 1965 and then it jumps to 1999.

By the way, the 1999 NEC at the end of article 336.30 (b) does refer to NM-B rather than NMB. I used the term NMB because I didn't know any better. Now I can say I used to know it but forgot.

336-30. General. Nonmetallic-sheathed cable shall com*-
ply with (a) and (b).


(a) Construction. The outer cable sheath shall be a non*-
metallic material.


(1) Type NM. The overall covering shall be flame re*-
tardant and moisture resistant.


(2) Type NMC. The overall covering shall be flame
retardant, moisture resistant, fungus resistant, and corrosion
resistant.


(3) Type NMS. Type NMS cable is a factory assembly
of insulated power, communications, and signaling conduc*-
tors enclosed within a common sheath of moisture-resistant,
flame-retardant, nonmetallic material. The sheath shall be
applied so as to separate the power conductors from the
communications and signaling conductors. The signaling
conductors shall be permitted to be shielded. An optional
outer jacket shall be permitted.


FPN: For composite optical cable, see Sections 770-4 and
770-52


(b) Conductors. The insulated power conductors shall be
one of the types listed in Table 310-13 that is suitable for
branch-circuit wiring or one that is identified for use in these
cables.
The power conductors shall be sizes No. 14 through
No.2 with copper conductors or sizes No. 12 through No.2
with aluminum or copper-clad aluminum conductors.
The signaling conductors shall comply with Section
780-5.
In addition to the insulated conductors, the cable shall
be permitted to have an insulated or bare conductor for
equipment grounding purposes only. Where provided, the
grounding conductor shall be sized in accordance with Arti*-
cle 250.
Conductors shall be rated at 90?C (194?F).


FPN: Types NM, NMC, and NMS cable identified by the
markings NM-B, NMC-B, and NMS-B meet this require*-
ment.

[Jerry Peck]

I have some significant holes in my Electric Code archive that I guess I am going to have to plug. You wouldn't happen to know any free-to-cheap sources for out-of-date NEC (preferrably handbooks), would you? The oldest that I have is (I believe) the 1965 and then it jumps to 1999.

I don't know of NFPA online free codes go back that far (just checked, it does: https://www.nfpa.org/codes-and-standards/all-codes-and-standards/list-of-codes-and-standards/detail?code=70 ).

But not the handbook (which has the explanatory information) ... and NFPA makes it about as user UNfriendly as they can to use the free online version.


By the way, the 1999 NEC at the end of article 336.30 (b) does refer to NM-B rather than NMB. I used the term NMB because I didn't know any better. Now I can say I used to know it but forgot.
.
..
FPN: Types NM, NMC, and NMS cable identified by the
markings NM-B, NMC-B, and NMS-B meet this require*-
ment.

Okay, so I got NM-B from having seen it that way before.

Makes sense, it started out as NM, then went to NM (60C) NMA (75C) and NMB (90C), then ALL NM became 90C (NMB), and at some point later it likely went to NM-B.

It likely changed because NM (60C) had limited uses - installed with any part of it in an attic or even outside walls and it required derating, which made it of limited use.

And because there was NM, NMA, and NMB, it made it a nightmare for contractors to use the correct type in the proper locations, and for inspectors to have to check EVERY run of NM cable to see if it was NMB on it, then have it replaced if it was in an attic and only marked NM. Changing all conductors to being 90C rated made it all NMB (then NM-B), eliminating those mistakes.

[Gunnar Alquist]

I would also guess that the cost difference between the 60-C and 90-C insulation was negligible, providing further incentive to eliminate the less practical cable.

[jack davenport]

NMB cable is rated for 90 degree as per the manufactures and the listing of the cable.

NMB is LIMITED to 60 degree as far as the ampacity is concerned (by The National Electric Code)
One uses the 90 degree column in the NEC for derating and such BUT the 60 degree column for ampacity.
For example a # 8 awg NMB cable is rated for 55 amps at 90 degree BUT limited to 60 Degree which limits it to 40 amps.

Maybe this is what the electrician was thinking about ?

[Jerry Peck]

Their electrician has apparently stated that the NMB cable entering the box in the second pic is rated for 60? C but since it is going directly to a fixture rather than a box it should be rated for 90? C instead.


NMB is LIMITED to 60 degree as far as the ampacity is concerned (by The National Electric Code)
One uses the 90 degree column in the NEC for derating and such BUT the 60 degree column for ampacity.
For example a # 8 awg NMB cable is rated for 55 amps at 90 degree BUT limited to 60 Degree which limits it to 40 amps.

Maybe this is what the electrician was thinking about ?

Possible, but that's certainly a twist around the clock to arrive at that possibility.

[Gunnar Alquist]

NMB cable is rated for 90 degree as per the manufactures and the listing of the cable. NMB is LIMITED to 60 degree as far as the ampacity is concerned (by The National Electric Code) One uses the 90 degree column in the NEC for derating and such BUT the 60 degree column for ampacity. For example a # 8 awg NMB cable is rated for 55 amps at 90 degree BUT limited to 60 Degree which limits it to 40 amps. Maybe this is what the electrician was thinking about ?


Possible, but that's certainly a twist around the clock to arrive at that possibility.

I would have to find and re-read the email and I no longer really care. This particular inspection has had somewhere in excess of 35 emails so far. Plus, I did not receive an email directly from the electrician, but through the client's husband. So, I don't have his exact wording. There are likely errors in translation.

[Joe Martin]

Looks like over-sized yellow 12-2 NM-B cable to me? It terminates in a junction box, just because the box is integral to the fixture doesn't make it any less of a junction box. What concerns me more is that I don't see cable connectors or a clamps in any of the junction boxes.

[Gunnar Alquist]

What concerns me more is that I don't see cable connectors or a clamps in any of the junction boxes.

Joe,

I addressed that in my report and that was not in question.

[Dave Ruth]

"And after 2001 (suppliers were still allowed to sell 'white' NM cable which was in stock until they ran out of stock,"

Does NEC mention color coding of outer sheath of NMB?

[Gunnar Alquist]

"And after 2001 (suppliers were still allowed to sell 'white' NM cable which was in stock until they ran out of stock,"

Does NEC mention color coding of outer sheath of NMB?

I looked in Article 334 of the 2014 NEC and did not find anything about the color of the sheath. This is probably ASTM or NEMA standard.

[Dave Ruth]

I looked in Article 334 of the 2014 NEC and did not find anything about the color of the sheath. This is probably ASTM or NEMA standard.
I'm not sure about standards, always thought it was manufacturers choice

[Jerry Peck]

NEMA Type NM-B Cable Jacket Color Coding for Conductor Size Identification

https://www.nema.org/Technical/Documents/Type%20NM-B%20Cable%20Jacket%20Color%20Coding%20for%20Conduc tor%20Size%20Idenification.pdf (https://www.nema.org/Technical/Documents/Type%20NM-B%20Cable%20Jacket%20Color%20Coding%20for%20Conduc tor%20Size%20Idenification.pdf)


There is no specific color code in use for NM-B cable with 8 AWG or larger conductors.

This color coding system was developed to aid those who sell, install, and inspect Type NM-Bcable so that the cable size can easily be identified, to reduce mistakes resulting from the use ofan incorrect conductor size.

It should be noted that this color coding system is not a requirement of NFPA 70, NationalElectrical Code?(NEC?) or UL 719, Safety Standard for Nonmetallic-Sheathed Cable. TypeNM-B can be produced and sold without using this color code. As such, the print legend, whichis required by the NEC?, should be used to verify the conductor size.

[Dave Ruth]

Ty Jerry Peck

[ROBERT YOUNG]

This one took me by surprise and I am trying to figure out exactly how to research it. I would very much appreciate some direction from some of the electrical code experts.

Old home (particularly for this area - 1872) that has been largely remodeled. It had knob & tube wiring, but has been completely replaced (as best as I can tell without opening walls & ceilings).

Their electrician has apparently stated that the NMB cable entering the box in the second pic is rated for 60? C but since it is going directly to a fixture rather than a box it should be rated for 90? C instead.

I was under the impression that most recessed fixtures got around that by providing a junction as a part of the fixture. The 60? C cable would be connected at the provided box and the fixture itself would have 90? C wiring between the box and the fixture.

At this point, I do not know when the home was rewired. Since there is both yellow and white NMB, I suspect the wiring has been done over a period of time rather than all at once. I do not believe that they are looking for me to pay for this, but it was something that took me by surprise. Unfortunately, I do not have any other images than those that I have posted.

3441734418

Morning, Gunner.
Like any cable, type, CU/AL, AWG, and potential energy = heat.

Your question; "since it is going directly to a fixture rather than a box it should be rated for 90 C instead."
I say, no.
The cable AWG downstream relates to upstream cable ><20% kinda/sortof:confused:

So, if the MAX cable ampacity is 60C downstream, it, 60C MAX, is maintained when other cables terminate upstream. Theoretically that cable will not surpass 60C MAX unless other vulnerabilities come into play like a transformer.

I think OHM's law comes into play when larger cable terminate on smaller cables on the same circuit and how that may/would/could effect connect devices.
That's my take on your question.

[Jerry Peck]

Morning, Gunner.
Like any cable, type, CU/AL, AWG, and potential energy = heat.
.
.
So, if the MAX cable ampacity is 60C downstream, it, 60C MAX, is maintained when other cables terminate upstream.

Robert,

The "heat" part is correct.

I did not include parts of your post to avoid a longer post and having others have to read it twice.

1) The 90C is for the "heat" at the termination an in the box.

2) The 90C also allows for a higher "heat" ambient that the NM cable travels through.

3) The 90C additionally allows for "heat" build-up for multiconductor cables which are bundled and/or where spacing between cables is not maintained.

The 60C ONLY applies to the maximum overcurrent device rating.

Going back to 2) and 3) above - those 90C ratings are used to derate the allowable ampacity of the circuit under the conditions it is installed.

I.e., install 90C NM cable through a 160F attic in Texas and that entire cable, from end to end, must be derated to compensate for that ambient "heat".

I.e., install 90C NM cables next to each other for long runs and the cables will "heat" up from each other's "heat" and ALL those cables, for their entire length from end to end need to be derated to compensate for that "heat" buildup.

I.e. do both of the above and that 90C rated NM cable may likely have to be increased in size to allow for the compensation needed for both conditions.

[ROBERT YOUNG]

As to the OP's thread title, 60? vs 90? C - NMB, heat is the underlying condition to safety.

From what I understand, and help me here if am am wrong.
1: An NMD branch circuit cable terminates in a junction box. Circuit cable rated 60C.
Please: Don't get into the breaker/OCPD's yet. Heat is heat.
2: An NMB cable for a luminary in/at that circuit enclosure is NMB cable rated at 90C.

Please, explain to me how the heat rating can increase if the NMB cable AWG was considered and luminary installed correctly?

[Gunnar Alquist]

This may also may be a manufacturer's installation requirement. In the past, I do recall having seen 90C mentioned in installation instructions of some light fixtures. If that is a manufacturer's requirement, then 90C wire would be necessary.

[Jerry Peck]

As to the OP's thread title, 60? vs 90? C - NMB, heat is the underlying condition to safety.

From what I understand, and help me here if am am wrong.
1: An NMD branch circuit cable terminates in a junction box. Circuit cable rated 60C.
Please: Don't get into the breaker/OCPD's yet. Heat is heat.
2: An NMB cable for a luminary in/at that circuit enclosure is NMB cable rated at 90C.

Please, explain to me how the heat rating can increase if the NMB cable AWG was considered and luminary installed correctly?

First, let's clarify this part: "heat rating can increase if the NMB cable AWG" 60C/75C/90C INSULATION as no relationship to AWG CONDUCTOR SIZE.

Then, I suspect that "1: An NMD" was a typo and you meant '1: An NMB', correct?

Finally, this part "Please: Don't get into the breaker/OCPD's yet. Heat is heat." can't be avoided when discussion circuit size and rating.

I know, I know, I didn't answer anything, all I did was seek clarifications.

[ROBERT YOUNG]

First, let's clarify this part: "heat rating can increase if the NMB cable AWG" 60C/75C/90C INSULATION as no relationship to AWG CONDUCTOR SIZE.

Then, I suspect that "1: An NMD" was a typo and you meant '1: An NMB', correct?

Finally, this part "Please: Don't get into the breaker/OCPD's yet. Heat is heat." can't be avoided when discussion circuit size and rating.

I know, I know, I didn't answer anything, all I did was seek clarifications.

Sorry for the late reply, Jerry. Executor, Exhaustion leading to Lung Infection, Doctor, Antibiotics. I am sure we have all been there, exhaustion, illness, at one time or another.

Anywho. ... I misread the OP's, Gunner's inquiry. "Their electrician has apparently stated, 'the NMB cable entering the box in the second pic is rated for 60? C'
Gunner's inquiry; 'since it is going directly to a fixture rather than a box it should be rated for 90? C.'

Getting past my misunderstanding of Gunners inquiry, I was under the understanding, there is NMB and NMD cables. NMD rated 60C. NMB rated 90C. Pic below.
34470
My hypotheses, the NMB cable terminated at a NMD cable. The NMD 60C cable was the circuit. The NMB cable went from the box to the fixture.

Leaving that aside, and while starting to recover, I found this article from IAEI; Wire Temperature Ratings and Terminations (https://iaeimagazine.org/magazine/2000/03/16/wire-temperature-ratings-and-terminations/) that might shed some light on the rules.

So Sorry for the mix-up Gunner, Jerry, Members. I have taken time off.

[Jerry Peck]

Robert,

There was the old NM (60C), NMA (75C), NMB (90C), and NMC.

Plain old NM and NMA are gone to history (to my understanding), leaving only NMB and NMC.

[ROBERT YOUNG]

TYPO. on the 60. Should have read 90.

Non-metallic (NM), Romex.

[Jerry Peck]

Robert,

There was the old NM (60C), NMA (75C), NMB (90C), and NMC.

Plain old NM and NMA are gone to history (to my understanding), leaving only NMB and NMC.

See this post below and its attachments from the 1984 NEC Handbook - it explains it:
- http://www.inspectionnews.net/home_inspection/electrical-systems-home-inspection-and-commercial-inspection/54829-60-vs-90-c-nmb.html#post284738

[mary theresa craig]

let me take a shot at this. I have 15 yrs residential electrical experience. The only time I have seen non-metallic sheathed cable rated at 90 degrees used, was for a large motor appliance with a continuous demand factor, such as a furnace. Especially if the length of the cable exceeds 50' from distribution to disconnect. Because the furnace, or AC, requires large amounts of power, immediately and continuously, conductors will heat up and require insulation that withstands higher temps. This is also the reason these circuits are calculated at 125% of their kw rating when calculating panel box loads in family dwellings and most other appliance circuits, 75% of their kw rating. I have never seen or used NM cable rated at 90 degrees smaller than a #8.
here are some rules of thumb that will Always apply for "over-current protection".
Never use over-sized conductors for a circuit in which it is intended. if the circuit overloads the conductor will not heat up and trip the breaker. damage will occur to the wiring and devices on that circuit.also, larger wires may not fit in the lugs of the breaker or fixture.
Never use an over-sized breaker for a circuit for which it is intended. the cable will heat up and melt the breaker before it trips the breaker.
Also, never downgrade along the path of a circuit. you may upgrade "1" level. for a 20 amp circuit upgrade from 12 gauge wire to #10. If the load of a circuit requires the use of a conductor with a higher temperature rating, That should not change through out the circuit.
Thanks
Theresa

- - - Updated - - -

let me take a shot at this. I have 15 yrs residential electrical experience. The only time I have seen non-metallic sheathed cable rated at 90 degrees used, was for a large motor appliance with a continuous demand factor, such as a furnace. Especially if the length of the cable exceeds 50' from distribution to disconnect. Because the furnace, or AC, requires large amounts of power, immediately and continuously, conductors will heat up and require insulation that withstands higher temps. This is also the reason these circuits are calculated at 125% of their kw rating when calculating panel box loads in family dwellings and most other appliance circuits, 75% of their kw rating. I have never seen or used NM cable rated at 90 degrees smaller than a #8.
here are some rules of thumb that will Always apply for "over-current protection".
Never use over-sized conductors for a circuit in which it is intended. if the circuit overloads the conductor will not heat up and trip the breaker. damage will occur to the wiring and devices on that circuit.also, larger wires may not fit in the lugs of the breaker or fixture.
Never use an over-sized breaker for a circuit for which it is intended. the cable will heat up and melt the breaker before it trips the breaker.
Also, never downgrade along the path of a circuit. you may upgrade "1" level. for a 20 amp circuit upgrade from 12 gauge wire to #10. If the load of a circuit requires the use of a conductor with a higher temperature rating, That should not change through out the circuit.
Thanks
Theresa

[Jerry Peck]

I have 15 yrs residential electrical experience. The only time I have seen non-metallic sheathed cable rated at 90 degrees used, ...

Any NM cable made for use under the 1984 NEC or later is 90?C rated, thus I'm sure that you've seen it used.

Sounds like you may be describing 'where you needed to apply derating to it'.

However, if you only applied derating for length of the run, and did not apply ambient derating first, the resulting ampacity you arrived at was likely not correct (unless no ambient derating was necessary due to the full cable run not going through a location with elevated ambient temperature).

And there were no other derating conditions either (bundling/lack of maintaining spacing/going through holes in wood top plates which are sealed with foam, caulk/etc. There are multiple conditions which require derating to be applied.

Length of circuit is not a "derating" condition per se, it is a voltage drop issue. Instead of derating and using a larger conductor size because of that, a larger conductor size is needed because of voltage drop over the length of the conductor (which are treated similar to resistors for voltage drop calculations because of their resistance, given per 1,000 feet for the calculation).

Southwire has a good voltage drop calculator, free online use.