Effectiveness of 1920's armored cable ground

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
(A) 320.100 is referenced by the (2011) NEC definition of type AC cable, so it is invoked every time the words "type AC cable" are used in the modern NEC.

(B) As demonstrated above, a preponderance of the available data shows that old BX without a bonding strip fails to satisfy 320.108.

Cheers, Wayne
Wayne, your ability to generalize knows no bounds.
 

wwhitney

Senior Member
Location
Berkeley, CA
Wayne, your ability to generalize knows no bounds.
This should be obvious, but the way a definition works is that whenever you see the word being defined, you can substitute the definition text without changing the meaning.

So 250.118(8) has the meaning: Armor of "A fabricated assembly of insulated conductors in a flexible interlocked metallic armor. See 320.100." as provided in 320.108.

Ungrammatical in this form, but it references 320.100.

Cheers, Wayne
 

wwhitney

Senior Member
Location
Berkeley, CA
To directly answer your question, 2011 & 2014 NEC 250.118(8) declares that "the armor of Type AC cable" is an acceptable Equipment Grounding Conductor, with the caveat to evaluate it as an "adequate path for fault current". the NEC says YES, there is an EGC present to extend on the modern method unless it is not "adequate".
If we ignore the 320.100 issue, I'm going to agree with you on the above, with the elaboration that the NEC also says it has to be "low-impedance". [250.118(8) => 320.108 => 250.4(A)(5)]

Now, what is adequate and low-impedance? The obvious choice is to look to the UL standard for armored cable. Its first standard for maximum "ohmic resistance" for armored cable was adopted as advisory in 1929 and mandatory in 1941 (Sleights, section 2.2). That standard is 1.5 ohms/100 feet for #14 armored cable (it has since been lower).

Among the combined samples tested by Dini and Sleights, less than 10% met this standard.

Cheers, Wayne
 

user 100

Senior Member
Location
texas
I think reducing this discussion into bullet points will be very helpful.

-Unbonded BX cable was recognized by the NEC as an EGC at one point in time, and was code compliant at the time of its installation.

- The UL standard for AC cable was revised and updated so that unbonded BX does not meet the UL construction standard for type AC cable, and therefore it's an obsolete wiring method (like knob and tube, ungrounded NM cable and reduced ground NM cable).

-Unbonded BX cable is not listed in the current edition of the NEC as a suitable equipment grounding means.

-Extensions and modifications to branch circuits, as well as receptacle replacement, must meet the current edition of the NEC. For most of us, that's the 2014 or 2011 NEC.

-Modern wiring extensions and receptacles must include an equipment grounding means.

Putting all of these facts (not opinions) together, we can easily conclude that unbonded BX cable cannot be used an EGC for installation of new 3-wire receptacles, or new branches and extensions to an existing circuit wired with unbonded BX cable.
I think the nm w/reduced egc could sort of still be compliant- 250.118 mentions copper conductor ( 250.122 gives us sizes, probably making that a moot point). FWIW, 406's grounding means doesn't do it for me- you are trying to connect an egc to new rec, not "grounding means."

I see no issue safety wise w/ a #16 egc in rec replacement- provided it's "verified", the joints are good and visible, (none of that goofy backwrap, or only twisted egc bundle w/ no connector in kind of crap, etc), but it's cheaper, easier, and definitely code compliant to just gfci.
 

user 100

Senior Member
Location
texas
Wanted to ask a related question... bx/ac predates cloth nm, two wire....why was the latter ever a legal install? When did no grounding become an option over marginal grounding? Anyone know for about how many years it was used? I think 1965 would have been the latest 2 wire nm was used; how early was it used?
I believe that 2 wire nm caught on because it was cheaper and less hassle to install. The earliest I have read nm was installed was in the 1920's.


The egc just wasn't considered important- most homes throughout the early 1900s didn't have metal cased appliances like refrigerators, freezers etc- most everything was 2 prong, for many years most of those two examples given only had a 2 wire plug. Even today, if you think about it, how much stuff in your house needs an egc?

The NEC did however a rule that went wayyyy baaack that stated something like that metal boxes within "x" distance of grounded objects (think old steel plumbing) had to be bonded- however this was not enforced a lot. The code gradually changed and started requiring grounded outlets in more and more areas. Those old rules are why you will find grounded recs and switches/light fixtures in the area around the kitchen sink, bathroom, or the porch, etc but no where else in the house.

The NEC finally started requiring all recs in a home to be grounded in the 1962 code, but that wasn't adopted in many areas right away. Another thing ec's would do is continue to use 2 wire outlets even w/ the new cable that had an egc- many ahjs only required the outlet be grounded, not of a grounding variety.:)
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
This should be obvious, but the way a definition works is that whenever you see the word being defined, you can substitute the definition text without changing the meaning.

So 250.118(8) has the meaning: Armor of "A fabricated assembly of insulated conductors in a flexible interlocked metallic armor. See 320.100." as provided in 320.108.

Ungrammatical in this form, but it references 320.100.
Wayne, you do realize you are applying the 320.2 definition of the term "Armored Cable, Type AC" to words in 250.118(8) that do not USE THAT TERM. I understand that you want 250.118(8) to say: "Armor of Type AC armored cable as provided in 320.108."

But, it does not. The red, bold, underlined word "armored" is not used in 250.118(8).
 

Fulthrotl

~~Please excuse the mess. Sig under construction~~
I have rarely seen old BX in decent condition. If I had to strip and reconnect an old piece, the conductor insulation would crumble right at the cut of the sheath. I mostly was able to get customer to replace it. Sometimes I would slide a heat shrink tube over the wire into the sheath. I only did that a few times and quit, as it was worrying me so much. I have seen knob & tube jobs that held up far better than BX.
at 9 pages into this thread, delving into the last 100 years of code subtleties,
with subtle nuances and inflections, etc. it still comes down to the fact that
it's freaking old wiring, almost always having suffered the years of fiddling with
poorly, and for that reason alone, is a good candidate for replacement.

i don't run across it personally very often, but for me, it kinda goes right alongside
with old panels by a manufacturer at the end of the alphabet. i'll replace it when
i have to interact with it, unless it's in good shape, which i've not seen much of,
but to be honest, i don't want the liability of putting my hands on it, and having
it fail three months later of old age.

let's just go back to thinwall, and pulling wire. metal pipe, metal enclosures,
and pull a ground wire, just to be sure.....
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
. . .it's freaking old wiring, almost always having suffered the years of fiddling with poorly, and for that reason alone, is a good candidate for replacement.

i don't run across it personally very often, but for me, it kinda goes right alongside with old panels by a manufacturer at the end of the alphabet. i'll replace it when i have to interact with it, unless it's in good shape, which i've not seen much of, but to be honest, i don't want the liability of putting my hands on it, and having it fail three months later of old age.
I believe you offer a reasonable and balanced approach. It is right to be cautious with Armored Cable and to verify that the EGC is "adequate". Regrettably, "adequate" is not explained procedurally by the NEC and we have to collaborate with AHJs and clients to solve the meaning.

To be clear, I work in a Metro of 3 million souls, that has a HUGE installed base of dwellings and businesses that are wired partially, or completely, in non-bonding-strip Type AC armored cable, and I work on it almost every day. The Metro does not keep erupting in fire from this old cable. (Things that make you go, "Hmmm.")

I am pushing back, here on this Forum, against the claims by others that "BX was never, and is not now, an EGC."
 

wwhitney

Senior Member
Location
Berkeley, CA
The red, bold, underlined word "armored" is not used in 250.118(8).
Try searching the current NEC for the term "type AC". You will see that that the phrases "type AC armored cable" and "type AC cable" are used interchangeably. Article 320 itself uses primarily the term "type AC cable". To suggest that a distinction is intended is ridiculous.

Cheers, Wayne
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
FWIW, 406's grounding means doesn't do it for me- you are trying to connect an egc to new rec, not "grounding means."
Remember, 406.4(D)(1), in addition to using "grounding means" also includes "equipment grounding conductor."
2014 NEC
406.4 General Installation Requirements.
(D) Replacements.
Replacement of receptacles shall comply with 406.4(D)(1) through (D)(6), as applicable.
(1) Grounding-Type Receptacles. Where a grounding means exists in the receptacle enclosure or an equipment grounding conductor is installed in accordance with 250.130(C), grounding-type receptacles shall be used and shall be connected to the equipment grounding conductor in accordance with 406.4(C) or 250.130(C).
Once one gets to seeing that the 2014 NEC 250.118(8) says that all "Type AC cable" has armor that is an EGC, then 406.4(D)(1) falls into place as inescapable.
 

JFletcher

Senior Member
Location
Williamsburg, VA
I believe that 2 wire nm caught on because it was cheaper and less hassle to install. The earliest I have read nm was installed was in the 1920's.


The egc just wasn't considered important- most homes throughout the early 1900s didn't have metal cased appliances like refrigerators, freezers etc- most everything was 2 prong, for many years most of those two examples given only had a 2 wire plug. Even today, if you think about it, how much stuff in your house needs an egc?

The NEC did however a rule that went wayyyy baaack that stated something like that metal boxes within "x" distance of grounded objects (think old steel plumbing) had to be bonded- however this was not enforced a lot. The code gradually changed and started requiring grounded outlets in more and more areas. Those old rules are why you will find grounded recs and switches/light fixtures in the area around the kitchen sink, bathroom, or the porch, etc but no where else in the house.

The NEC finally started requiring all recs in a home to be grounded in the 1962 code, but that wasn't adopted in many areas right away. Another thing ec's would do is continue to use 2 wire outlets even w/ the new cable that had an egc- many ahjs only required the outlet be grounded, not of a grounding variety.:)
thank you for the reply. as for what needs a ground, that's a whole different topic. :cool:

eta: the wire insulation(TW?) in that old AC seems to be more problematic than a ground path. Maybe it's just been my luck, but more times than not the insulation has disintegrated to the point of needing replacement.
 
Last edited:

wwhitney

Senior Member
Location
Berkeley, CA
I am pushing back, here on this Forum, against the claims by others that "BX was never, and is not now, an EGC."
I'm sorry, did you show us a version of the NEC that (a) uses the term EGC, (b) doesn't require type AC cable to have a bond wire, and (c) lists the armor of such type AC cable as an EGC?

I'm pretty sure that has never been true at any point in time. Regardless, the current 250.118(8) excludes cable armor without a bonding strip.

Cheers, Wayne
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
To suggest that a distinction is intended is ridiculous.
Opinion.

To suggest that 2011 & 2014 320.2 Definition "Armored Cable, Type AC" is the ONLY DEFINITION of "Type AC cable" is where your broad brush generalization fails. The four word term and the three word term are not equated by published statement that limits one to having only to accept 2011 & 2014 NEC 320.100 bonding strip construction ONLY.



Original 1918 National Electrical Code requiring Type AC armored cable cannot be excluded from the meaning of the three word term "Type AC cable". David Dini, P.E. of UL, and John Sleights of Travelers Engineering Laboratory both publish that non-bonding strip armored cable is historically used as a grounding means, and was manufactured, tested, and evaluated as such, and is still a grounding means.
 

wwhitney

Senior Member
Location
Berkeley, CA
(A) Article 320 "Armored Cable: Type AC" uses the term "type AC cable" throughout. This establishes as a fact that in the current NEC, type AC cable and type AC armored cable are synonyms.

(B) 250.118 says "Armor of Type AC cable". To suggest the meaning would be different if it said "Armor of Type AC armored cable" boggles the mind. The writer didn't include the word "armored" because it would be redundent--if the cable has armor, it is obviously armored.

Cheers, Wayne
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
(A) Article 320 "Armored Cable: Type AC" uses the term "type AC cable" throughout. This establishes as a fact that in the current NEC, type AC cable and type AC armored cable are synonyms.

(B) 250.118 says "Armor of Type AC cable". To suggest the meaning would be different if it said "Armor of Type AC armored cable" boggles the mind. The writer didn't include the word "armored" because it would be redundent--if the cable has armor, it is obviously armored.
In your opinion. That & $1.25 gives me a $1.25 cup of coffee. Your mind boggling is a personal problem, in my opinion.
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
I'm sorry, did you show us a version of the NEC that (a) uses the term EGC, (b) doesn't require type AC cable to have a bond wire, and (c) lists the armor of such type AC cable as an EGC?

I'm pretty sure that has never been true at any point in time.
Wayne, please.

I am weary of repeating things to you again and again. Please get some old Code books and school yourself.

I have posted in numerous places on this Forum, as have others, that the term Equipment Grounding Conductor did not come into definition in the NEC until the second half of the Twentieth Century. Other language was used to mean the same thing. You do have John Sleight's excellent summary of the history of the use of the armor of armored cable as an equipment grounding means and he makes this very point that I am saying right now.
 

wwhitney

Senior Member
Location
Berkeley, CA
P.S. The text of the 2011 NEC uses the phrase "type AC" 56 times. 9 of those times some aspect of the armor is under discussion, so the armor is specifically referred to. Also, the title, scope, and definition in Article 320 uses the phrase "armored cable, type AC" plus for some reason 368.65 uses the phrase "type AC armored cable". The other 43 instances omit "armor" or "armored", including 16 uses in Article 320 itself.

So if anything "type AC cable" is the usual NEC term for the product covered by Article 320.

Cheers, Wayne
 

wwhitney

Senior Member
Location
Berkeley, CA
In your opinion.
Let's be clear here. You are saying that if 250.118(8) said "Armor of Type AC armored cable", you would agree that it excludes old BX without a bonding strip, but that since it says "Armor of Type AC cable," it does not?

If so, I rest my case with respect to 320.2, as I doubt anyone will agree with that.

Cheers, Wayne
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
P.S. The text of the 2011 NEC uses the phrase "type AC" 56 times. 9 of those times some aspect of the armor is under discussion, so the armor is specifically referred to. Also, the title, scope, and definition in Article 320 uses the phrase "armored cable, type AC" plus for some reason 368.65 uses the phrase "type AC armored cable". The other 43 instances omit "armor" or "armored", including 16 uses in Article 320 itself.

So if anything "type AC cable" is the usual NEC term for the product covered by Article 320.

Cheers, Wayne
[Ennui] Yes Wayne. . . Type AC cable is used in the Code. . . expand your search to track it over all the Codes. . .[/Ennui]
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
Let's be clear here. You are saying that if 250.118(8) said "Armor of Type AC armored cable", you would agree that it excludes old BX without a bonding strip, but that since it says "Armor of Type AC cable," it does not?

If so, I rest my case with respect to 320.2, as I doubt anyone will agree with that.

Cheers, Wayne
[Ennui]See post #99.[/Ennui]
 
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