Effectiveness of 1920's armored cable ground

wwhitney

Senior Member
Location
Berkeley, CA
Please get some old Code books and school yourself.
I grant that in past codes old BX cable armor without a bonding strip was compliantly used as a grounding means. So if you want to verify whether an old installation was done compliantly at the time, you'd need the old Code books.

But for current work, you only need the current NEC. And under the current NEC, that old BX cable armor does not qualify as an EGC. The contents of old Code books are immaterial for making that determination.

Cheers, Wayne
 

wwhitney

Senior Member
Location
Berkeley, CA
Hi Al,

I'm sorry your forehead is hurting.

One thing I don't understand about the distinction you create between the 2011 NEC phrases "type AC cable" and "type AC armored cable". If the phrase "type AC cable" includes old BX without a bonding strip, so that you can say that it meets 250.118(8), who do you do about 320.100? It also uses the phrase "type AC cable". When the new inspector in town cites 320.100 to disallow the use of the old BX armor as an EGC, what do you say?

Cheers, Wayne
 

wwhitney

Senior Member
Location
Berkeley, CA
Hi Al,

Apparently being confronted with the implausibility of your "type AC cable" versus "type AC armored cable" interpretation is putting you to sleep.

So how about my comments on the 320.108 issue, that you never responded to? When you use BX cable armor without a bonding strip as an EGC, do you verify that it meets the historical UL standard of 1.5 ohms/100 feet for #14 conductors?

Cheers, Wayne


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.
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
Your continued refusal to educate yourself in the historic living Code in an attempt to execute verbal "gotchas" is transparent.

I have repeated myself to you and even shown you the extreme repetition, to no apparent avail. I will speak to fresh comment / query, but I'm done repeating.
 

big john

Senior Member
Location
Portland, ME
Al, reading this thread as an outside observer your position seems to be that since AC-without-bonding was once a code compliant EGC that it must still be a code compliant method because it hasn't been specifically rescinded?

That would be like saying it's acceptable for me to wire new houses in K&T. Codes and standards constantly evolve, so I really don't follow that argument.
 

kwired

Electron manager
Location
NE Nebraska
Al, reading this thread as an outside observer your position seems to be that since AC-without-bonding was once a code compliant EGC that it must still be a code compliant method because it hasn't been specifically rescinded?

That would be like saying it's acceptable for me to wire new houses in K&T. Codes and standards constantly evolve, so I really don't follow that argument.
I think this has been touched on but I will mention it again, it is sort of like the issue a few years back when standard compression fittings were deemed no longer acceptable as raintight fittings. Though I think that was a joke, you don't see everyone rushing out to replace all the previously existing fittings that are in areas that get wet.
 

big john

Senior Member
Location
Portland, ME
Funny you mention raintight fittings, it was the example I originally thought of using.

I'm certain there are plenty of BX installs that will adequately clear a fault. But there seems to be evidence that some of them won't, and create a fire hazard in the process of trying, hence the amendment changing the description of AC to include a bond wire.

It makes me want to try and find a 75' piece of BX and see how it passes current on a test set.
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
Al, reading this thread as an outside observer your position seems to be that since AC-without-bonding was once a code compliant EGC that it must still be a code compliant method because it hasn't been specifically rescinded?
My position is, because "Armored Cable Type AC" is the cable that the 1913 NEC thru to the late Fifties NEC required to be installed (when the rule in the Armored Cable article published the change in the construction of the cable to require the bonding strip) was not changed to Armored Cable Type AC-B (or some other changed "Type" designation the way NM changed to NM-B) there is, today, no way to make 2014 NEC 250.118(8) apply only to one Armored Cable Type AC over another type of Armored Cable Type AC, in my opinion.

Over the years from enforcement of the 1913 NEC until the 1959 NEC, countless utilization equipment was connected to the Main Bonding Jumper and the Grounding Electrode System via the armor of non-bonding strip Type AC cable. The utilization equipment electrical connection to the GES did not cease with the addition of the bonding strip under the 1959 NEC rule, but rather continues forward in time.
That would be like saying it's acceptable for me to wire new houses in K&T. Codes and standards constantly evolve, so I really don't follow that argument.
This is different than ungrounded K&T. To be clear, I have stated numerous time in explanation of my position, that I am not advocating using non-bonding strip Type AC cable in new construction. I do, as previously stated, continue to state that connecting new wire to an unmodified existing Type AC cable's wires in an existing junction box is not new construction of the Type AC cable.
 

wwhitney

Senior Member
Location
Berkeley, CA
Your continued refusal to educate yourself in the historic living Code in an attempt to execute verbal "gotchas" is transparent.
First, let me apologize for letting my posts earlier today become snippy. I found the whole "type AC cable" versus "type AC armored cable" thing exasperating.

Second, that's the only verbal gotcha going on here. A plain reading of the current NEC does not allow cable armor without a bonding strip as an EGC, and you to have go through wordsmithing gymnastics to get anywhere close to a justification for it.

Given the above, I agree it is time for us to stop repeating ourselves.

Cheers, Wayne
 

wwhitney

Senior Member
Location
Berkeley, CA
I think this has been touched on but I will mention it again, it is sort of like the issue a few years back when standard compression fittings were deemed no longer acceptable as raintight fittings. Though I think that was a joke, you don't see everyone rushing out to replace all the previously existing fittings that are in areas that get wet.
Sure, but if you had to take to apart one of those fittings to rework a conduit run, would you reuse the old compression fitting, or use a new one that meets the updated standard? Ignoring for the moment whether or not the change was a joke, suppose it was justified.

Cheers, Wayne
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
I'm certain there are plenty of BX installs that will adequately clear a fault.
I absolutely agree. I work on them regularly.

But there seems to be evidence that some of them won't, and create a fire hazard in the process of trying, hence the amendment changing the description of AC to include a bond wire.
The adding of the bonding wire improves the performance of the armor, but does not fix the fire hazard as we are still instructed by 320.108 to ensure the EGC is "adequate" with modern bonded Type AC armored cable systems. I prefer to say it the way David Dini published it:

Residential Electrical System Aging Research Project
July 1, 2008
David A. Dini, P.E., Underwriters Laboratories Inc.

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.
 

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".
So let me ask how do you evaluate whether it is an "adequate path for fault current"? I don't believe you've addressed that.

Cheers, Wayne
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
So let me ask how do you evaluate whether it is an "adequate path for fault current"? I don't believe you've addressed that.
Yes, Wayne, I did.

Regrettably, "adequate" is not explained procedurally by the NEC and we have to collaborate with AHJs and clients to solve the meaning.
 
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