Effectiveness of 1920's armored cable ground

[al hildenbrand]

correct me if I'm wrong- wouldn't it need two paths to be allowed? (aside from updated new code) a conductor of some sort and only then- armor clad..... "two or more of the following" 250.118...

The language isn't what you are remembering. If it were, EMT, alone, would not be an EGC (which it is.)

2014 NEC

250.118 Types of Equipment Grounding Conductors. The equipment grounding conductor run with or enclosing the circuit conductors shall be one or more or a combination of the following:

 

[rambojoe]

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...

 

[tkb]

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...

If you mean in the US, then yes it is still allowed for EMT and AC. MC also if it is the new MCap style.

 

[al hildenbrand]

you need a conductor along with emt,mc,ac ect.

Not according to the National Electrical Code.

I thought we stopped using pipe as the equipment back in 96?!

No.

your're kidding right? is it allowed in your county? I am genuinely curious...

Not kidding. What copy of the Code do you work out of? Your profile says you are under the "2007"? Is that a local designation to you?

 

[rambojoe]

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....)

 

[wwhitney]

I have established that Type AC armor is an EGC from direct citations from the Codes, including the 2014 NEC.

Al, would it be fair to summarize your position as "the code under which it was installed called it Type AC cable, so in all future codes the term Type AC cable includes it"? I think it would be fair to summarize my position as "when the construction requirements for Type AC cable changed to require the bonding strip, the old stuff ceased to be Type AC cable."

Anyway, there is certainly some controversy on this topic, if not in your immediate geographic region.

Cheers, Wayne

 

[al hildenbrand]

. . .there is certainly some controversy on this topic, if not in your immediate geographic region.

I stand by my QUOTES from the published National Electrical Code. Go back to the citations I posted in this and earlier threads and read that original language.

If you want to stand by your opinion, can you please substantiate it with something other than opinion?

 

[wwhitney]

If you want to stand by your opinion, can you please substantiate it with something other than opinion?

Here's a quick version (from the 2011 NEC), there's no point in reprising all the points of our prior discussion:

250.118(8) lists "Armor of Type AC cable as provided in 320.108" as a type of EGC. Two reasons that BX cable armor without a bonding strip fails to qualify:

(A) 320.108 says "Type AC cable shall provide an adequate path for fault current as required by 250.4(A)(5) or (B)(4) to act as an equipment grounding conductor." In the typical case of a grounded system, 250.4(A)(5) applies and refers to "a low-impedance circuit facilitating the operation of the overcurrent device". We know that old BX cable armor without a bonding strip does not meet this requirement, so it does not meet 320.108 and thus fails to qualify under 250.118(8). [For an ungrounded system, 250.4(B)(4) applies and leads to a similar conclusion.]

(B) Moreover, the current NEC doesn't even recognize old BX cable as Type AC cable. 320.100 is incorporated into the definition of type AC cable, and it says "Type AC cable shall have an armor of flexible metal tape and shall have an internal bonding strip of copper or aluminum in intimate contact with the armor for its entire length." Older BX cable without such a bonding strip is no longer considered type AC cable, regardless of what prior codes may or may not have referred to it as.

Cheers, Wayne

 

[al hildenbrand]

We know that old BX cable armor without a bonding strip does not meet this requirement, . . .

This is opinion. Can you please move off of restating this meme with published studies? There must be good laboratory analysis of this somewhere, right? I'd love to see some hard evidence.

 

[wwhitney]

This is opinion. Can you please move off of restating this meme with published studies? There must be good laboratory analysis of this somewhere, right? I'd love to see some hard evidence.

Do you otherwise agree with Reason A? If so, I'll look into this. If not, what other disagreement do you have with Reason A?

Reason B still applies, regardless of whether unbonded BX cable armor provides a low-impedance fault path.

Cheers, Wayne

 

[al hildenbrand]

Do you otherwise agree with Reason A? If so, I'll look into this. If not, what other disagreement do you have with Reason A?

Reason B still applies, regardless of whether unbonded BX cable armor provides a low-impedance fault path.

Cheers, Wayne

So, you are bargaining to draw me into opinion vs. opinion? Please, just facts. Substantiate the hazard, please.

 

[wwhitney]

So, you are bargaining to draw me into opinion vs. opinion? Please, just facts. Substantiate the hazard, please.

Well, I just didn't want to waste my time verifying what appears to be common knowledge if you are just going to disagree elsewhere. But OK, I'll waste a few minutes. Here you go:

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". Unfortunately the article text is not freely available, but the abstract says in part:

Testing was performed on samples of aged cables removed from service to determine impedance and temperature rise of the armor when conducting AC current. The results were compared to the DC resistance of the armor as well as the applicable Underwriters Laboratories standard. The performance of cable samples was also tested in construction configurations likely to be encountered in buildings. Results indicate that ground fault currents conducted via the armor of older cable constructions can result in fire and shock hazards where the impedance and circuit characteristics limit the fault current to below the trip level of the circuit overcurrent protective device. Temperature rise of the armor can easily exceed the rating of the conductor insulation contained therein and in some cases present a fire hazard to combustible material in contact with the cable.

That's the result of 1 minute of googling, I'm sure there's more out there.

Cheers, Wayne

 

[al hildenbrand]

Wayne, I am not asking this lightly. Do you honestly think I haven't searched?

The abstract is opinion of studies. What are the studies?

 

[iwire]

I understand that this is your opinion.

I have established that Type AC armor is an EGC from direct citations from the Codes, including the 2014 NEC. I have been driven by my reality under multiple AHJs in my State and Metro.

The fact remains that old BX is not modern AC and is not constructed as modern AC is required.

 

[al hildenbrand]

The fact remains that old BX is not modern AC and is not constructed as modern AC is required.

I agree with you that "armored cable Type AC" has been constructed in different manners over the time from the 1913 NEC. 250.118(8) does not differentiate between your distinctions, but rather, only references 320.108 (not 320.100).

So, this comes down to the meme that replacing a receptacle device with a grounding-type receptacle device in pre-bonding-wire armored cable wiring method causes fire, loss and death.

Show me the studies that make this "what we know."

 

[user 100]

I've replaced 2 prong with the same- I dont think they make tr 2-prong, but sometimes its about making it better, not right.

It's right and it's perfectly legal to do so- tr not required for 2 prong replacement:

406.12 exception (4)

"Nongrounding receptacles used for replacements as permitted in 406.4 (D)(2)(A)

 

[K8MHZ]

The fact remains that old BX is not modern AC and is not constructed as modern AC is required.

I was thinking along the same lines, but can't really find anything in the NEC that comes right out and says old BX type cable no longer meets the specifications of AC cable. I wish I could. But I can't. If it met the specs when it was installed, it seems like the code would allow it to be used as installed.

My take is, so what if the NEC allows old, nasty BX to be used as an EGC, I personally won't do it. I try to stay a few hairs above being a 'bare minimum' electrician.

 

[wwhitney]

Wayne, I am not asking this lightly. Do you honestly think I haven't searched?

I haven't really considered it. Anyway, here's an earlier report from the same author that's not behind a paywall:

http://ewh.ieee.org/cmte/pses/ffat/support/RESAReport.pdf

I've only scanned it, but it shows that old BX cable without a bonding strip has an impedance of between 2 and 3 ohms per 100 ft, using 9 samples from 4 different states. I believe that's comparable to 24 AWG copper! I would say that is not "low impedance" and thus fails 320.108.

The abstract is opinion of studies. What are the studies?

I'm happy to take the abstract at face value, rather than pay for the full text. You disagree?

Cheers, Wayne

 

[tkb]

I was thinking along the same lines, but can't really find anything in the NEC that comes right out and says old BX type cable no longer meets the specifications of AC cable. I wish I could. But I can't. If it met the specs when it was installed, it seems like the code would allow it to be used as installed.

My take is, so what if the NEC allows old, nasty BX to be used as an EGC, I personally won't do it. I try to stay a few hairs above being a 'bare minimum' electrician.

I don't think the old BX still has a valid listing.
It's like when EMT compression fittings listing changed and they were not listed as rain tite anymore.

 

[user 100]

I don't think the old BX still has a valid listing.

It doesn't- 320.100 says so. I too gave grandfathering this stuff a little consideration in the other thread, that is until the thing about listing came up. This is what makes vintage BX different from other older wiring methods like nm w/undersized ground or old rigid/emt- those are ​still listed egcs when you replace an old receptacle w/a grounding variety.

Interestingly, 406.4(D)(1) mentions "grounding means", which may come across as a little ambiguous, but it is not,(imo)-under the 2014 you are replacing a receptacle, the conductor to be terminated to the egc terminal is supposed to be an egc, and 250.118 tells you acceptable egc's. On the other hand, 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.