Effectiveness of 1920's armored cable ground

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wwhitney said:
http://ewh.ieee.org/cmte/pses/ffat/support/RESAReport.pdf
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Yes. I've read this also. David Dini's technical report: Residential Electrical System Aging Research Project. Note that David Dini is a P.E. with Underwriters Laboratory.

It's a very informative read.
3.2 Armored Cable Armored Cable first appeared in the 1903 NEC, but didn’t become popular until around 1930, and is still a popular wiring method today. The armor of AC cable systems is tested for grounding and can provide a suitable equipment grounding path. AC cable made after 1959 requires a No. 16 AWG aluminum bonding strip under the armor to help improve the conductivity of this path.
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12.1 Effects of Aging Older armored cable installed before the 1960s may not have a bonding strip (e.g., bare aluminum conductor) installed between the metal armor and the current carrying conductors to help supplement the use of the armor as an effective grounding path. Older examples of this cable that were found without this bonding strip exhibited armor resistances that in some cases were more than double the original design value.
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user 100 said:
. . . if an ahj considers it acceptable to use old bx casing as an egc then so be it- they have decided what they believe is best for their constituents- local amendments to the NEC get made all the time.
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I realize you probably aren't talking specifically about my many AHJs. I just want to clarify, that the State of Minnesota, and my various Metro AHJs all work from a 100% un-altered or amended NEC, cycle after cycle. That is, without local amendment, they approve the armor of Type AC armored cable, with bonding strip or not, as an equipment grounding conductor.
 
al hildenbrand said:
I realize you probably aren't talking specifically about my many AHJs. I just want to clarify, that the State of Minnesota, and my various Metro AHJs all work from a 100% un-altered or amended NEC, cycle after cycle. That is, without local amendment, they approve the armor of Type AC armored cable, with bonding strip or not, as an equipment grounding conductor.
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Then they interpret it as being legal and acceptable w/out amendment, they may look at it from the perspective of not having any issues that crop up, lack of an epidemic, iow's. There was one state California I think that ended up ignoring 394.12(5) and started allowing insulation around K&T (with conditions iirc) because they determined there was no problem. Look at Michigan and the afci move recently (they amended in writing of course)- they decided there was part of the code they didn't like and they've ditched it.:D
 
rambojoe said:
ill search for the other threads before I get off topic from the op but still- you need a conductor along with emt,mc,ac ect. I thought we stopped using pipe as the equipment back in 96?! your're kidding right? is it allowed in your county? I am genuinely curious...
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Been answered already but I agree - NO.

rambojoe said:
fair enough. however, every ground up I've been on has required it in the specs. I'll still count on pulling one. i'm just surprised I guess. i work under what ever code book the inspector uses, but i have quite a few laying around. and.... found the thread(s). holy crap its a long one. time for coffee. (thread on armor clad as....)
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Specifications often do call for a wire type EGC to be installed, but NEC would be met with raceway or cable sheaths alone in most of those instances. Health care applications - NEC does require raceway or cable sheath that is a qualifying EGC as well as a wire type EGC in patient care areas though.
 
ActionDave said:
Used as installed would include using two wire recpts.
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I challenge you to show, in the old NECs, that non-bonding-strip Type AC was not allowed to have grounding-type receptacle outlets installed on the wiring method.
 
ActionDave said:
They didn't exist.
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So, you're saying grounding-type receptacle devices don't exist prior to the advent of the 1959 addition of the armored cable bonding strip? Can you share a document that claims such a late date of the first existence of grounding-type receptacle outlet devices?
 
al hildenbrand said:
So, you're saying grounding-type receptacle devices don't exist prior to the advent of the 1959 addition of the armored cable bonding strip? Can you share a document that claims such a late date of the first existence of grounding-type receptacle outlet devices?
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I can't but from experience seeing older wiring seems as though they certainly were not common or even non existent. Anything you ever see that has a third conductor had a 120/240 rating on it. Old AC cable installs may have had grounded sheath but they always installed non grounding type receptacles, if you would have run into a three wire receptacle it wasn't a 5-15 it was a 120/240 rated receptacle.
 
Take a read of AC power plugs and sockets. Well down in the article you will find:

The earthed consumer plug has several claimants to its invention. A 1911 book[28] dealing with the electrical products of A. P. Lundberg & Sons of London describes the "Tripin" earthed plug available in 2.5 amp and 5 amp models. The pin configuration of the "Tripin" appears virtually identical to modern BS 546 plugs. In her 1914 book Electric cooking, heating, cleaning, etc.[29] Maud Lucas Lancaster mentions an earthed iron-clad plug and socket by the English firm of Reyrolle and Co. The earliest American patent application for an earthed plug appears to be 11 January 1915 by George P. Knapp, on behalf of the Harvey Hubbell company.[30] This patent covers the use of an earthing pin which extends further than the other two contacts to ensure that it is engaged first. The configuration of the socket was not operable with existing two-contact unearthed plugs. Other earthed sockets that are widely used in the US today are operable with unearthed plugs.
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220px-Tripin_1911.jpg


Going to Reference [30] at the bottom of the Wikipedia article leads one to U.S. Patent 1,179,728 with a great patent drawing that you can blow up and scroll around in.

Lastly, prior to the 1962 NEC requirement for all 15 and 20 Amp 125 Volt receptacles to be of the grounding-type, the Code, instead, had a list of locations and utilization equipment that was required to be "grounded." Just because one rarely, if ever, sees a pre-1962 NEC grounding-type receptacle on an armored cable wiring method does not prove that Type AC armored cable without bonding strip could only have nongrounding-type receptacles installed to it.
 
kwired said:
Been answered already but I agree - NO.

Specifications often do call for a wire type EGC to be installed, but NEC would be met with raceway or cable sheaths alone in most of those instances. Health care applications - NEC does require raceway or cable sheath that is a qualifying EGC as well as a wire type EGC in patient care areas though.
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I realized my confusion. it was a san Francisco rule (on emt, rigid, bx/ac ) needing grounds. think earthquakes. anyhoo, thanks for the answer, I appreciate it. (no pvc either anywhere btw in s.f., back then anyways)
 
al hildenbrand said:
Take a read of AC power plugs and sockets. Well down in the article you will find.....
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Fine, you found a white buffalo. The NEC had section on using grounding type recpts in the '20s and '30s? '40s??



Lastly, prior to the 1962 NEC requirement for all 15 and 20 Amp 125 Volt receptacles to be of the grounding-type, the Code, instead, had a list of locations and utilization equipment that was required to be "grounded." Just because one rarely, if ever, sees a pre-1962 NEC grounding-type receptacle on an armored cable wiring method does not prove that Type AC armored cable without bonding strip could only have nongrounding-type receptacles installed to it.
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And the construction of Type AC changed because it was obvious that there was a problem with the old stuff.
 
Alright Al, it's pretty simple now:

Per "Residential Electrical System Aging Research Project", the 9 samples of armored cable without a bonding strip, from 6 houses in 4 states, all had an armor resistance of between 2 and 3 ohms/100 ft. That is too high to "provide an adequate path for fault current" as required in 320.108. In fact, it exceeds the listing requirement at the time of manufacture (1.50 ohms/100 ft for #14 BX cable).

250.118 requires type AC cable to comply with 320.108 in order to be an EGC. So your old BX cable without a bonding strip is not currently a recognized EGC. End of story.

Cheers, Wayne
 
ActionDave said:
Well the fact is there was a change in Type AC construction. I wonder what the reason for that was?
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Most recently, in Post # 43 I answered your question by quoting the published work of David Dini, P.E., Underwriters Laboratories, Inc.

Residential Electrical System Aging Research Project
July 1, 2008
David A. Dini, P.E., Underwriters Laboratories Inc.
3.2 Armored Cable
Armored Cable first appeared in the 1903 NEC, but didn’t become popular until around 1930, and is still a popular wiring method today. The armor of AC cable systems is tested for grounding and can provide a suitable equipment grounding path. AC cable made after 1959 requires a No. 16 AWG aluminum bonding strip under the armor to help improve the conductivity of this path.
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Note, that while writing on behalf of UL, David Dini states that "the armor of AC cable systems is tested for grounding and can provide a suitable equipment grounding path." He declares this for AC cable systems, without distinction. And in direct answer to your question, Dini says the change in construction was "to help improve", Dini does not say the change was to fix a problem.

Dini's published UL document correlates with the Code citations I've provided elsewhere on this Forum that document armored cable Type AC first appeared in the 1913 NEC and, even then, the armor was a suitable equipment grounding path.
 
al hildenbrand said:
Opinion. Yours.
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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?

Cheers, Wayne
 
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