# Pulling THHN through BX



## CoreyOnTheBrink (Apr 9, 2021)

Hey I have a question. Have any of you tried to pull #14THHN through old two-wire BX cable? None of my receptacles at my house have equipment grounds and I want to add them but had the thought that maybe I could do it w/o having to try to fish NMB into my old boxes. So I would use the old cloth insulated two wire to pull in (3)#14 wires. It’s my house so I thought it would be a good test run for something I haven’t tried before, plus it would be nice to know if this is a viable option for other resi jobs.


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## 99cents (Aug 20, 2012)

Try it and, guaranteed, after five minutes you will give up.


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## BlackHowling (Feb 27, 2013)

CoreyOnTheBrink said:


> Hey I have a question. Have any of you tried to pull #14THHN through old two-wire BX cable? None of my receptacles at my house have equipment grounds and I want to add them but had the thought that maybe I could do it w/o having to try to fish NMB into my old boxes. So I would use the old cloth insulated two wire to pull in (3)#14 wires. It’s my house so I thought it would be a good test run for something I haven’t tried before, plus it would be nice to know if this is a viable option for other resi jobs.


There's a reason the conductors in the cable don't just fall out on their own. 

Sent from my SM-G975W using Tapatalk


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## SteveBayshore (Apr 7, 2013)

The old armor and sometimes the tiny aluminum strip inside of newer BX are the equipment ground. Make sure it's not fed with or has knob and tube jumpers someplace. Test to see if the boxes are actually grounded. If so, install ground jumpers from the grounded box and install grounded receptacles. Install GFI receptacles in the first device on the circuit and grounded type receptacles after and label the new receptacles GFCI protected. 
I haven't done this _trick_ in thirty years, any up to date residential guys know if this is still legal?


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## Southeast Power (Jan 18, 2009)

BX by definition uses the armored jacket as the ground.


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## ohm it hertz (Dec 2, 2020)

If the BX is continuous back to the panel, why rewire? Just ground pigtail to the box and confirm continuity.


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## 460 Delta (May 9, 2018)

Southeast Power said:


> BX by definition uses the armored jacket as the ground.


And it will turn into a nice Chromalox/toaster coil if and when you get a substantial ground fault.


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## SteveBayshore (Apr 7, 2013)

460 Delta said:


> And it will turn into a nice Chromalox/toaster coil if and when you get a substantial ground fault.


I have seen greenfield (FMC) catch fire in a couple of places where it wasn't installed adequately. One was a commercial bakers type of mixer in a (styro) foam type factory. The mixer was raised raised and lowered into the kettle by a gear motor. The 240 volt mixer flex got caught on the side of the mixing bowl when the mixer was raised. The flex stretched into a coil and the internal ground conductor pulled out of the terminal at one end. One of the phase conductors pulled and cut into the connector. The red hot coil of stretched out flex burned half of the old building down.


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## CoreyOnTheBrink (Apr 9, 2021)

Southeast Power said:


> BX by definition uses the armored jacket as the ground.


Ok then it must not technically be BX then because I would think then I would have a ground on my receptacles.


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## Dennis Alwon (May 9, 2009)

Southeast Power said:


> BX by definition uses the armored jacket as the ground.


Not always true in the past. The old BX without the bare steel strand is not legal to use as a ground. There have been pictures of bx glowing red when there was a dead short but not enough to open the breaker


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## Dennis Alwon (May 9, 2009)

CoreyOnTheBrink said:


> Ok then it must not technically be BX then because I would think then I would have a ground on my receptacles.



Nope. Years ago they did not have 3 wire outlets and they only used them in the kitchen. Why I don't know.


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## Dennis Alwon (May 9, 2009)

BX is not a raceway, it is a cable there is no way you can pull the wire out unless the run is straight and maybe not more than 6'. 

2 Choices.... If the bx has the steel bond wire then put a ground screw in the back of the box with a pigtail to the grounded outlet. If it doesn't have the bonding wire either leave it or pull it out from below-- not easy to do and run NM.


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## MechanicalDVR (Dec 29, 2007)

Dennis Alwon said:


> Nope. Years ago they *did not have 3 wire outlets* and *they only used them in the kitchen.* Why I don't know.


HUH???

What are you trying to say?


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## Dennis Alwon (May 9, 2009)

MechanicalDVR said:


> HUH???
> 
> What are you trying to say?


There was a time when 3 wire outlets were only used in the kitchen not in the rest of the house. Before that they didn't even use them in the kitchen


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## MechanicalDVR (Dec 29, 2007)

Dennis Alwon said:


> There was a time when 3 wire outlets were only used in the kitchen not in the rest of the house. Before that they didn't even use them in the kitchen


I wasn't getting how they used them if they didn't have them.

Frm past experience I'd say kitchen receptacles were upgraded for appliance use, something the rest of the house didn't need done.


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## CoreyOnTheBrink (Apr 9, 2021)

Thanks for the input, folks. I’ll just get a new house.


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## ohm it hertz (Dec 2, 2020)

I like your enthusiasm.


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## wiz1997 (Mar 30, 2021)

If you lay the BX out straight, strip out one end, clamp the wires in a vise, then pull the outer jacket off.

You can get about 10 feat to pull out fairly easily.

Run fish tape through, pull the #14 in.

Done it a few times when a 1/2" flex wouldn't fit through a hole in the metal frame of the equipment.

I doubt you could pull the conductors out of anything with a bend or two in it.


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## lectriguy101 (Nov 5, 2014)

CoreyOnTheBrink said:


> Hey I have a question. Have any of you tried to pull #14THHN through old two-wire BX cable? None of my receptacles at my house have equipment grounds and I want to add them but had the thought that maybe I could do it w/o having to try to fish NMB into my old boxes. So I would use the old cloth insulated two wire to pull in (3)#14 wires. It’s my house so I thought it would be a good test run for something I haven’t tried before, plus it would be nice to know if this is a viable option for other resi jobs.


If you have BX and metal boxes you should be able to use the bx for a ground and simply put a ground wire on the box providing the bx is in a metal box clamped to box with metal clamps


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## ohm it hertz (Dec 2, 2020)

lectriguy101 said:


> If you have BX and metal boxes you should be able to use the bx for a ground and simply put a ground wire on the box providing the bx is in a metal box clamped to box with metal clamps


_And_ returns to the panel. For all we know the bx was added to the K&T which was landed in the panel without a grounding conductor. I find it this way often.


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## danielplace1962 (Mar 24, 2014)

Whether you ground to the boxes with a tail or not if they are receptacles with a ground on them and if it is a metal box the receptacles are grounding from it already so adding a tail for most part isn't making anything worse that couldn't already occur only that they would for sure be getting a solid ground to every one for sure. Or use of self grounding outlets if not already.


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## hornetd (Oct 30, 2014)

Southeast Power said:


> BX by definition uses the armored jacket as the ground.


First I have to agree with others that although it sometimes works getting the old wires out is very tedious to do and I didn't find it worth the time except on rather short fairly straight runs. If it is the later version of Type AC Cable with the Aluminum bonding strip inside the jacket it is even harder to do. There is such a thing as 3/8ths flexible metallic Conduit but I've never seen it on a supply house shelf. Admittedly I never had reason to look for it so it may have been there all along. The Armor of Type AC cable is not listed as flexible Metallic Conduit (FMC) so I would think that we should not try to use it as FMC. You can get 3 THHN wires in the old armor so as to provide a high quality Equipment Grounding Conductor (EGC) but I always found it rather difficult to do.

BX is actually the original Type AC cable which was made, under a patent held by General Electric, in the company's Bronx, New York. factory. As was General Electric's practice with all of their products the original armored cable had a card stock tag wire tied to each roll with BX in large letters to show which GE factory had made it and that is why most of us call AC cable BX to this day. The original BX cable did not have a bonding strip in it just as it's first Non Metallic Cable; Type NMC; competitor, Romex, did not have any kind of Equipment Grounding Conductor (EGC). I say this to remind people that there is a lot of BX still installed and you cannot depend on it's spiral tape armor to serve as an EGC. Even if you get a good result with a field expediant or a purpose made instrument, such as an Ideal Suretest, ground impedance test the conductivity of the armor can change in a rather short time. Steel is only a fair conductor and rust is a terrible conductor. It does not take a lot of visible rusting to open the electrical pathway between the turns of the armor and cause it to behave as a rather long coil with a high impedance. All it does take is the very first layer of rust which is not readily visible. That impedance will slow the current flow from a ground fault and delay the operation of the circuit's Over Current Protective Device (OCPD). That allows an arc or resistive heating fault to continue longer with the attendant likelihood of ignition of adjacent combustibles. I urge all of you to treat any of the remaining installed original BX even more cautiously than you would the original Romex. With it's unbonded spiral metal tape armor original BX is worse that the original NMC cable. Not only does it often have no effective ground fault current pathway it may have a continuous coil impedance wrapped around it as well. 

-- 
Tom Horne


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## CoreyOnTheBrink (Apr 9, 2021)

That’s a great post thank you for sharing.


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## Djea3 (Mar 8, 2019)

I would forget the ground and install a GFCI receptacle in the first device box. From there you can go ahead and use 3 prong receptacles and will have ground fault protection. Agreed you will have no ground but most products today are two prong.

If you have to have a ground, check with your local codes. It may be legal to run an isolated ground from the nearest grounded circuit (any ground landed in the main or sub-panel) to the location that must be grounded. Again, this is a local code issue. I have always thought that having a ground, even if it is run separately from the conductors is better than not having a ground.


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## eddy current (Feb 28, 2009)

Do they still sell that crap with the bonding strip in it down south? 
Has not been available up here for decades. All we have is AC-90 (we call it BX but it is not) which has a bare copper bond wire and a paper wrapping around all the conductors


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## Djea3 (Mar 8, 2019)

eddy current said:


> Do they still sell that crap with the bonding strip in it down south?
> Has not been available up here for decades. All we have is AC-90 (we call it BX but it is not) which has a bare copper bond wire and a paper wrapping around all the conductors


We call it MX or BX in FL or Calif. and all that I have installed are with ground most stranded wire but sometimes solid and never seen paper wrap. 10 gage and under generally, we had a commercial job that spec'd 10 gage stranded for receptacles and 12 gage for lighting. That was insane given the number of circuits, dedicated circuits and LED lighting involved. Mostly commercial but occasionally into a garage or other area where NM would be exposed or build a chase if a lot of wires are involved and NM. Never heard anyone use the term AC-90.
I ran MX through my entire detached garage, 12 gage for utility circuits and 14 for lighting. Although I did install switches for lighting, I turn off all breakers including all receptacles on the sub-panel (QO series) instead.


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## danielplace1962 (Mar 24, 2014)

Djea3 said:


> *We call it MX or BX in FL *or Calif. and all that I have installed are with ground most stranded wire but sometimes solid and never seen paper wrap. 10 gage and under generally, we had a commercial job that spec'd 10 gage stranded for receptacles and 12 gage for lighting. That was insane given the number of circuits, dedicated circuits and LED lighting involved. Mostly commercial but occasionally into a garage or other area where NM would be exposed or build a chase if a lot of wires are involved and NM. Never heard anyone use the term AC-90.
> I ran MX through my entire detached garage, 12 gage for utility circuits and 14 for lighting. Although I did install switches for lighting, I turn off all breakers including all receptacles on the sub-panel (QO series) instead.


You mean MC or BX


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## 205490 (Jun 23, 2020)

Answering the original question; sounds like a waste of time, do it right, pull some circuits it's what we do.
Don't sell the house, KC housing market will continue to do well.


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## splatz (May 23, 2015)

CoreyOnTheBrink said:


> Hey I have a question. Have any of you tried to pull #14THHN through old two-wire BX cable? None of my receptacles at my house have equipment grounds and I want to add them but had the thought that maybe I could do it w/o having to try to fish NMB into my old boxes. So I would use the old cloth insulated two wire to pull in (3)#14 wires. It’s my house so I thought it would be a good test run for something I haven’t tried before, plus it would be nice to know if this is a viable option for other resi jobs.


I missed this first time around. One thing to remember, the new rules you can fish a ground wire to the box, this can be a lot easier than a full rewire. You can go back to the panel, bond to the GES, or bond to an EGC of a circuit from the same panel. 

The part I wonder about is whether it's acceptable to run a bare THHN for this or do you have to use a chapter 3 wiring method?


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## 460 Delta (May 9, 2018)

splatz said:


> I missed this first time around. One thing to remember, the new rules you can fish a ground wire to the box, this can be a lot easier than a full rewire. You can go back to the panel, bond to the GES, or bond to an EGC of a circuit from the same panel.
> 
> The part I wonder about is whether it's acceptable to run a bare THHN for this or do you have to use a chapter 3 wiring method?


I always took it as fish in a # 14-12 single wire, but that old saw of the AHJ “interpretation,” who knows. You would think they would make it as accommodating as possible to get an outlet grounded so people would actually do it.


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## Majewski (Jan 8, 2016)

LOL do it. then come to my house and rewire my nm with new thhn...then later, replace the strands in my feeders.


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## 460 Delta (May 9, 2018)

Majewski said:


> LOL do it. then come to my house and rewire my nm with new thhn...then later, replace the strands in my feeders.


Shouldn’t be too many outlets in a van down by the river.


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## Majewski (Jan 8, 2016)

460 Delta said:


> Shouldn’t be too many outlets in a van down by the river.


the entire sunroof is outlets


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## 460 Delta (May 9, 2018)

Majewski said:


> the entire sunroof is outlets


Is that so?


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## Majewski (Jan 8, 2016)

460 Delta said:


> Is that so?


t'is


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## 460 Delta (May 9, 2018)

Majewski said:


> t'is


I see.


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## hornetd (Oct 30, 2014)

SteveBayshore said:


> The old armor and sometimes the tiny aluminum strip inside of newer BX are the equipment ground. Make sure it's not fed with or has knob and tube jumpers someplace. Test to see if the boxes are actually grounded. If so, install ground jumpers from the grounded box and install grounded receptacles. Install GFI receptacles in the first device on the circuit and grounded type receptacles after and label the new receptacles GFCI protected.
> 
> I haven't done this _trick_ in thirty years, any up to date residential guys know if this is still legal?


I believe that is still permitted but there are a couple of points worth emphasizing. The first is that there are 2 generations of Armored Cable (AC). The first was a product of the General Electric Company. It did not have a bonding strip inside the armor. Why it came to be called BX was that everything shipped from a GE plant had a 2 letter code on it to indicate the GE factory at which it was made. That is why every single roll of the original armored cable, which was a patent protected product had a wire affixed card stock tag that had the Bronx factory's 2 letter "BX" code on it. Which is easier to say? "Armored Cable" or "BX." Which was easier for a new apprentice to identify when you sent them to get you another roll of cable. They could look for the tiny paper wrap somewhere on the cable which had the UL listing mark printed on it or you could say "Go down to the supply cache and get me a roll of BX, which was printed on card stock in 2 inch letters. That is why the 2 letter GE factory code BX is still used as a nick name for Armored Cable.

When field experience revealed that the interlocking steel tape alone did not provide an adequate fault current pathway the patented GE version lost it's UL listing. Several manufacturers began producing the second version of Armored Cable with an aluminum bonding strip inside the armor to bond the individual turns of the armor into a low impedance conductor which is suitable for use as an EGC.

Before assuming that a circuit wired with Armored Cable has an adequate fault current pathway you must test the impedance of that path. An Ideal Suretest Circuit Analyzer can do this test and give you the results automatically. Those testers run about $370 but if you have an expectation of ongoing residential service work then it will be worth it. To perform the test manually you must first test the voltage drop on the energized and Grounded Current Carrying Conductor in order to have a normal operating voltage to compare. Then apply same load to the energized conductor and armor, *very briefly*, while the same volt meter is connected to the same 2 points. Very briefly, in this context, means that you connect the load, I used a 1500 watt portable hair dryer, to the energized conductor and the GEC pathway under test. If the voltage does not drop to any significant degree, then you have a usable fault current path via the cable armor. Any significantly lower voltage means that it is not an acceptable fault current path.

If the circuit's fault current pathway does not show significant voltage drop under test then do as *SteveBayshore* suggested and bond the equipment grounding conductor of the receptacle to the box. Many really old electrical boxes do not have a threaded hole through the back of the box to except the 10/32 threaded grounding screw. You can drill and tap a hole but it is easier to use a grounding clip instead.







These clips are listed to connect the equipment grounding conductor jumper to a steel box. It is not be a code requirement to put a GFCI in such a circuit but if the panel will except a modern breaker I would install a combined Arc and Ground Fault Circuit Interrupter to guard against any later deterioration of the Ground Fault Current Path.

If the box does not have an effective Fault Current pathway you can establish 1 by any of the 6 methods stated in 250.130 Equipment Grounding Conductor Connections. This is the best practice remedy for the open ground condition at the receptacles you want to change to the Grounding type.

*250.130 Equipment Grounding Conductor Connections. … *For replacement of non–grounding-type receptacles with grounding-type receptacles and for branch-circuit extensions only in existing installations that do not have an equipment grounding conductor in the branch circuit, connections shall be permitted as indicated in 250.130(C).

250.130(C) Non-grounding Receptacle Replacement or Branch Circuit Extensions. The equipment grounding conductor of a grounding-type receptacle or a branch-circuit extension shall be permitted to be connected to any of the following:
(1) Any accessible point on the grounding electrode system as described in 250.50
(2) Any accessible point on the grounding electrode conductor
(3) The equipment grounding terminal bar within the enclosure where the branch circuit for the receptacle or branch circuit originates
(4) An equipment grounding conductor that is part of another branch circuit that originates from the enclosure where the branch circuit for the receptacle or branch circuit originates
(5) For grounded systems, the grounded service conductor within the service equipment enclosure
(6) For ungrounded systems, the grounding terminal bar within the service equipment enclosure

If for some legitimate reason you cannot run an EGC to one of those locations that is when you resort to using a GFCI feed through receptacle to protect the entire circuit.  This approach is specifically permitted by: 406.4(D)(2)(b), or 406.4(D)(2)(c).

406.4 General Installation Requirements. Receptacle outlets shall be located in branch circuits in accordance with Part III of Article 210. General installation requirements shall be in accordance with 406.4(A) through (F).
406.4(D) Replacements. Replacement of receptacles shall comply with 406.4(D)(1) through (D)(6), as applicable. Arc Fault Circuit-Interrupter type and Ground-Fault Circuit Interrupter type receptacles shall be installed in a readily accessible location.
(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).
(2) Non–Grounding-Type Receptacles. Where attachment to an equipment grounding conductor does not exist in the receptacle enclosure, the installation shall comply with (D)(2)(a), (D)(2)(b), or (D)(2)(c).
(a) A non–grounding-type receptacle(s) shall be permitted to be replaced with another non–grounding-type receptacle(s).
(b) A non–grounding-type receptacle(s) shall be permitted to be replaced with a ground-fault circuit interrupter type of receptacle(s). These receptacles shall be marked “No Equipment Ground.” An equipment grounding conductor shall not be connected from the ground-fault circuit interrupter-type receptacle to any outlet supplied from the ground-fault circuit-interrupter receptacle. 
(c) A non–grounding-type receptacle(s) shall be permitted to be replaced with a grounding-type receptacle(s) where supplied through a ground-fault circuit interrupter. Grounding-type receptacles supplied through the ground fault circuit interrupter shall be marked “GFCI Protected” and “No Equipment Ground.” An equipment grounding conductor shall not be connected between the grounding type receptacles.

Whenever you replace a 2 pole 2 wire receptacle with a 2 pole 3 wire receptacle You must not bond the receptacle’s Grounding Electrode Conductor terminal to those of other receptacles. Paragraph 406.4(D)(b) which allows replacement of a non-grounding receptacle with a GFCI ends with "An equipment grounding conductor shall not be connected from the ground-fault circuit interrupter-type receptacle to any outlet supplied from the ground-fault circuit-interrupter receptacle." 406.4(D)(c) ends with “An equipment grounding conductor shall not be connected between the grounding type receptacles.”

You install the GFCI as the receptacle outlet in the outlet box which is closest to the panel from which the circuit is supplied. If you cannot make a determination were that receptacle is located then install a GFCI Circuit Breaker in place of the standard breaker. If the outlet/s you want to change to the 2 pole, 3 wire grounding type is/are on a circuit which would require Arc Fault Circuit Interrupter protection under the code presently adopted as law in your jurisdiction you install it at the receptacle outlet which is closest to the panel from which the circuit is supplied. If you cannot determine were that receptacle is located then install a GFCI Circuit Breaker in place of the standard breaker. If the outlets you want to change to the 2 pole, 3 wire grounding type NEMA 5-15R is on a circuit which would require Arc Fault Circuit Interrupter protection under the code presently adopted as law in your jurisdiction you must install an AFCI.

Tom Horne


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## hornetd (Oct 30, 2014)

ohm it hertz said:


> If the BX is continuous back to the panel, why rewire? Just ground pigtail to the box and confirm continuity.


If it is actually BX, which is the 2 letter code for the General Electric Bronx factory were it was produced, then it is the original GE patented Armored Cable which did not have a bonding strip in the armor to provide inter turn continuity to the interlocking metal tape. Without that bonding strip the armor develops a layer of corrosion between the turns which turns it into a rather long coil inductor which makes it an effective impedance to the flow of fault current. By shunting out the turns with an aluminum strip the armor remains a continuous steel conductor with a comparatively large cross section. GE's Armored Cable lost it's UL listing when that affect became evident years after it was introduced. Since GE's patent did not include any bonding means it no longer protected them from competitors who began manufacturing the bonded version. 

I raise that to explain that it is dangerous to depend on the unbonded GE version of Armored Cable as an Equipment Grounding Conductor (EGC). If you can get the use of one, apply an Ideal Suretest Circuit Analyzer to the receptacle using the 3 wire pigtail adapter. If the impedance of the Fault Current pathway is low enough it will show it as good. If the impedance is higher than that of the Grounded Current Carrying Conductor (neutral) then it will indicate a high impedance ground. Those testers retail for ~$370 so check with everyone you know in the craft to see if they will let you borrow theirs. Say thank you with an adequate amount of their favorite libation. then you will know how to proceed. If you do a large amount of residential service work then it might be worth it to you to buy one. 

There is a manual method for doing the impedance test. Let me assure you that neither continuity or a low DC resistance will assure that it is a low impedance pathway for taking fault current back to it's source at a large enough amperage to quickly open the circuit's Over Current Protective Device and de-energize the fault before the heating it will cause ignites a "Fire of Electrical Origin." 

Tom Horne


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## hornetd (Oct 30, 2014)

splatz said:


> The part I wonder about is whether it's acceptable to run a bare THHN for this or do you have to use a chapter 3 wiring method?


Well I suppose some inspector could defeat the entire purpose of the new language by insisting on a Chapter 3 wiring method. If it were The way available to get something done I would use Armored Grounding Electrode Conductor cable if the distance was relatively short. I wonder if the smaller gauge versions of that are still made.

Tom Horne


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## Norcal (Mar 22, 2007)

danielplace1962 said:


> You mean MC or BX


MC and AC (BX) have different NEC articles and different installation requirements for each. AC art 320, MC art.330.


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