Effectiveness of 1920's armored cable ground

[al hildenbrand]

The average resistance in the report was 2.83 ohms/100 feet for the 8 samples of #14 BX cable without a bonding strip. That's between the resistance of #24 and #25 copper wire. Are you honestly saying you consider a 24 gauge EGC to be an adequate fault path?

In the words of David Dini:

Residential Electrical System Aging Research Project
July 1, 2008
David A. Dini, P.E., Underwriters Laboratories Inc.
12.0 Summary of Findings
Some of the houses may have reached their structural end-of-life before they were demolished, and for economic or other reasons, the last inhabitants of the house may not have adequately taken care of the electrical, mechanical, or plumbing aspects of the building. This appeared to be the case for houses AL-5, AL-9, MA-1, NY-1, NY-2, OR-1, and WI-1. The reader is cautioned about drawing conclusions about houses in general, especially when based on data from houses that may have been neglected and not adequately maintained by the owner or occupants prior to its demolition.

 

[Fulthrotl]

Fine, you found a white buffalo.

And the construction of Type AC changed because it was obvious that there was a problem with the old stuff.

hey! be respectful of the white buffalo.
as soon as i can get my hands on one,
i'm going to cross breed it with my unicorn,
as rumor has it that if you cross breed the two of them,
you end up with the rarest mythological creature of them all....






an honest politician.




btw, is it a male or female white buffalo? this is somewhat important
to my plan, as i only have a male unicorn.

 

[al hildenbrand]

hey! be respectful of the white buffalo.

[laughing out loud] :lol: [/laughing out loud]

 

[Fulthrotl]

but using the bx sheath as an EGC isn't gonna get a lot of rave reviews here.

to balance that out, however, we have Al, who we keep chained up in the root
cellar, and he comes out when this topic is aired. :happyyes:

 

[al hildenbrand]

to balance that out, however, we have Al, who we keep chained up in the root
cellar, and he comes out when this topic is aired. :happyyes:

Cookies! Feed me cookies!

 

[wwhitney]

I don't know Al, 9 out of 9 is pretty compelling, even if the author has used cautious language at a few points, which you have been quick to highlight.

Have you done any testing of your own? If not, then you have to use the data available, and it clearly shows that BX cable armor without a bonding strip is not an adequate fault clearing path. I don't think you'll find anyone in this forum who would agree that the equivalent of a 24 gauge copper wire is an NEC compliant EGC.

Cheers, Wayne

 

[al hildenbrand]

I don't know Al, 9 out of 9 is pretty compelling, even if the author has used cautious language at a few points, which you have been quick to highlight.

Have you done any testing of your own? If not, then you have to use the data available, and it clearly shows that BX cable armor without a bonding strip is not an adequate fault clearing path. I don't think you'll find anyone in this forum who would agree that the equivalent of a 24 gauge copper wire is an NEC compliant EGC.

So David Dini and UL is just too weak to hold up to your opinion. . . eh?

Show me in documented studies that any installing of grounding-type receptacles on an Article 320 armored cable system CAUSES fire, property loss or death.

 

[wwhitney]

Sorry, I'm out, you're more stubborn than I am, Al.

For everyone else, I'm sure the evidence presented so far is enough.

Cheers, Wayne

 

[JFletcher]

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?

 

[iwire]

Well the fact is there was a change in Type AC construction. I wonder what the reason for that was?

And those changes now mean old BX is not AC and no longer is an EGC.

But Al knows this as he refuses to answer the question I have asked a number of times.

If we use modern cable to extend from old BX do we have an EGC or not?

 

[wwhitney]

The 2nd link currently on a google search for "old bx cable armor impedance test" is to the 2011 article "An Evaluation of Old Armored Cables in Building Wiring Systems".

OK, I tracked down a copy of this paper by John Sleights. The testing done was more extensive than in the earlier paper by Dave Dini. Let me paraphrase the test results comparable to the earlier results in this thread:

34 samples of 9 to 10 feet in length of old two conductor 14 AWG BX cable without a bonding strip were tested to determine the armor impedance with a fault current of 15A. The observed impedances were from 0.87 to 6.63 ohms / 100ft, with an average of 3.78 ohms/100 ft. Only 4 of the samples showed an impedance of less than 1.5 ohms / 100 ft, which was the earliest historical standard for armor impedance that UL adopted (it is now lower).

The study has lots of other data, like temperature rises in open air and insulation, including some lab photos of cellulose insulation catching on fire from an old BX circuit on a modern circuit breaker.

So there you have it, 39 out of 43 samples agree that old BX cable armor with a bonding strip is not a low impedance fault path.

Cheers, Wayne

 

[jmellc]

Greenlee markets a great all-in-one drill and tap that works well for this:

These are great. I have gone through several sets of them. Not good for really heavy work but good for boxes and/or cleaning ragged threads.

 

[Fulthrotl]

The study has lots of other data, like temperature rises in open air and insulation, including some lab photos of cellulose insulation catching on fire from an old BX circuit on a modern circuit breaker.

So there you have it, 39 out of 43 samples agree that old BX cable armor with a bonding strip is not a low impedance fault path.
Cheers, Wayne

that's it! back in the root cellar for the both of you....
chain them out of each others reach, and give them
a browser to surf levarage points, and don't forget to
close the door to the cellar to keep the sound down....

if we keep them down there to ferment for about six
weeks, that will be about the time this topic resurfaces,
like the loch ness monster.

as for cross breeding the unicorn and white buffalo,
in light of our current political climate of gender indifference
in all things, i'll just use two males for the cross breeding.

hey, if it doesn't matter on bathroom signage, it can't
make any difference.

 

[peter d]

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.

 

[kwired]

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.

You forgot to mention white buffaloes or unicorns

 

[jmellc]

You forgot to mention white buffaloes or unicorns

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.

 

[peter d]

And those changes now mean old BX is not AC and no longer is an EGC.

But Al knows this as he refuses to answer the question I have asked a number of times.

If we use modern cable to extend from old BX do we have an EGC or not?

I would also like to hear Al's answer to that.

 

[al hildenbrand]

I think reducing this discussion into bullet points will be very helpful.

Putting all of these facts (not opinions) together, we can easily . . .

Peter, you do not use actual Code language in the bullet points, which I can. So your "opinion" that you are stating facts isn't yet really substantiated by the written language of the Code when it comes to the single key inflection point in your bullet point flow of logic below. That key inflection bullet point is what is contentious.

-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.

I agree, as demonstrated in many prior posts that quote passages from pre-1958 NEC editions, and as demonstrated with scans of actual historic NECs.

- 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).

I agree the construction standard was changed, as can be demonstrated by the changes in written language of the appropriate rule of the Armored Cable article through the 1950s into the early 1960s. I have not posted quotes of this "construction rule" from the NEC, but will be happy to do so if asked.

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

This is where you loose me, Peter. I can't find this in the 2014 or the 2011 NEC.

2011 & 2014 NEC 250.118(8) says (in toto), "Armor of Type AC cable as provided in 320.108". 320.100 is not invoked when describing the 250.118 Types of Equipment Grounding Conductors. I have shown in direct quotes and page scans of the old NECs, posted on this Forum several times, that armored cable, installed to the NEC of its original installation, has been Type AC since the 1913 NEC went into enforcement.

The designation "Type AC" in today's NEC does not give us a way to indicate that bonding strip armored cable is the ONLY Type AC allowed as an EGC, and that non-bonding strip armored cable is not allowed as an EGC. Rule 250.118(8) calls out ONLY the "armor", it does not say "armor and bonding strip" or some variation of words that get to the meaning of the AC construction rule 320.100.

-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.

I agree.

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

I agree.

 

[wwhitney]

2011 & 2014 NEC 250.118(8) says (in toto), "Armor of Type AC cable as provided in 320.108". 320.100 is not invoked when describing the 250.118 Types of Equipment Grounding Conductors.

(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

 

[al hildenbrand]

And those changes now mean old BX is not AC and no longer is an EGC.

The Code citations I have been posting disagree with this opinion of yours.

But Al knows this as he refuses to answer the question I have asked a number of times.

You know my mind better than what I write here? You are wrong, Bob, and are mis-characterizing what "I know".

If we use modern cable to extend from old BX do we have an EGC or not?

Sorry for dropping your ball, Bob. We never got back to this after I researched the original old NECs to learn that "BX" is never used in the NEC and that armored cable has be required to be "Type AC" since first specifically required by rule in the 1913 NEC.

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". In my Metro area with its huge installed base of armored cable systems, the answer to your question is YES, there is an EGC present to extend on the modern method unless it is not "adequate".