Effectiveness of 1920's armored cable ground

I have a situation where a customer wants to replace some of the original two-prong receptacles in a house from the 20's. I understand the options available in Article 406.4 (D) and although AC does satisfy the requirements for an equipment grounding conductor in and of itself, I am concerned that it would be better to simply replace with two-prong devices rather than to install grounded devices and rely on the integrity (continuity, effective impedance, etc.) of the original AC wiring method. The cables are connected to the boxes with a snap-in connector (no lock-nut) and I just don't think I want to count on these to provide a very good bond (I don't even know if they were intended to provide an effective grounding means when they were designed or installed). If i were to install grounded devices, I couldn't even use a grounding pigtail because there are no tapped holes in the boxes to attach it. I would have to use a clip or self-grounding devices. I just don't like it and don't feel good about it. I will ask the Dearborn, MI electrical department, but I wanted your opinions first.
 

__dan

Senior Member
If the house does not have a service change to a standard breaker panel, that would be my obvious first suggestion, suggest a service change and put the old BX they want to keep on GFI breakers.

If the panel is there, GFI breakers is the obvious direction to move in. Small subpanel for the GFI breaker seems a waste of time relatively.

The 3" x 2" switch receptacle boxes will be too small for the wire count to do any modifications. You may be limited to a wire count of two #14 ga plus ground. So if you want to stay grandfathered, you may be able to only replace what's there with same.

The BX may be grandfathered for equipment grounding IDK, it's possible, but the loads will be sensitive electronic equipment along with vacuums and table saws.. If you want to spend the customer's money wisely, I can see changing what's there for devices with same device, move the circuits up to GFI breaker supplied, and running new grounded direct lines for the present heavy loads and leaving the old wiring for small light convenience type loads.
 
Thanks for the feedback. Sounds like neither of you like the idea of depending on the existing AC for a reliable EGC either (I don't). Is that what I am hearing?

I am only talking about the general purpose outlets in bedrooms, living room and the ONE in the dining room. All kitchen, laundry, bathroom and basement receptacles are to be updated with new circuits.
 

GoldDigger

Moderator
Staff member
Thanks for the feedback. Sounds like neither of you like the idea of depending on the existing AC for a reliable EGC either (I don't). Is that what I am hearing?

I am only talking about the general purpose outlets in bedrooms, living room and the ONE in the dining room. All kitchen, laundry, bathroom and basement receptacles are to be updated with new circuits.
Depending on the sheath of old BX for EGC is asking for a fire if a ground fault ever develops which does not trip the OCPD. Tales of red glowing BX can be found in some other threads.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
If the BX or AC cable has a thin steel strip inside the armor and the connector is listed for grounding then the BX is suitable for use as an equipment grounding conductor.
 

JFletcher

Senior Member
Location
Williamsburg, VA
If the BX or AC cable has a thin steel strip inside the armor and the connector is listed for grounding then the BX is suitable for use as an equipment grounding conductor.
and it hasnt been hacked apart in previous renovations.

tmk, MI has temporarily abandoned all nec req's for afci breakers. I've replaced 2 prong with the same, or gfci. I dont think they make tr 2-prong, but sometimes its about making it better, not right.
 

peter d

Senior Member
Location
New England
There is no way I would ever trust old BX armor (without a bonding strip) as an EGC. I frequently observe corrosion at box clamp when I take apart or have to work on old BX systems, and deteriorated cable armor as well. Most of that old BX in my area was installed in the 1930's and has long since outlived its useful life.
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
. . . AC does satisfy the requirements for an equipment grounding conductor in and of itself, I am concerned that it would be better to simply replace with two-prong devices rather than to install grounded devices and rely on the integrity (continuity, effective impedance, etc.) of the original AC wiring method. The cables are connected to the boxes with a snap-in connector (no lock-nut) and I just don't think I want to count on these to provide a very good bond (I don't even know if they were intended to provide an effective grounding means when they were designed or installed). If i were to install grounded devices, I couldn't even use a grounding pigtail because there are no tapped holes in the boxes to attach it. I would have to use a clip or self-grounding devices. I just don't like it and don't feel good about it. I will ask the Dearborn, MI electrical department, but I wanted your opinions first.
The Code minimum is that since the 1913 NEC, all armored cable installed (to Code) has been Type AC. Today's list of acceptable Equipment Grounding Conductors includes the "armor of Type AC cable," 250.118(8). I agree with your statement that I bolded above.

I have lived and worked in a Metro of 3 million souls all my career. Historically, local ordinances required all power and light wiring in new construction be encased in metal for work that was done from the Thirties into the Seventies. As a result there is a huge amount of housing stock in this Metro of 3 million that is wired with "BX". I can anecdotally offer that Minneapolis - St. Paul is NOT consumed by BX armor ground fault fires.

In fact, IMO, 406.4(D)(1) guides one to use the existing EGC of Type AC cable armor to provide for grounding-type receptacles.
 

rambojoe

Senior Member
Location
phoenix az
because the bx has a snap in connector ill assume that its been messed with. does it in fact have the skinny AL ground in the cable? check at the panel. if so, great. if the cable is that old with the rubber/cloth insulation, don't be surprised if it gets a short after handling or bending it. in phoenix the heat just disintegrates the insulation. call backs, liability ect. could be whoever messed with it cut the ground at the conn...
I never do side work but one neighbor got me to help the old lady across the street when her indoor Edison fused panel mounted outside caught fire in a monsoon. EVERY damn bx (oven, swap cooler, gl's etc) disintegrated right in front of me! that was a long, long day. and made 80$ :/ I told ol lou, don't solicit work for me from retired public school teachers on a crappy pension!
 

Fulthrotl

~~Please excuse the mess. Sig under construction~~
Thanks for the feedback. Sounds like neither of you like the idea of depending on the existing AC for a reliable EGC either (I don't). Is that what I am hearing?

I am only talking about the general purpose outlets in bedrooms, living room and the ONE in the dining room. All kitchen, laundry, bathroom and basement receptacles are to be updated with new circuits.
i've seen a couple old installs around here that had a bond wire hitting all the boxes, not just kitchen and bath.
*if* there is a bare bond wire connecting the boxes, you may have a leg to stand on, but using the bx sheath
as an EGC isn't gonna get a lot of rave reviews here.

service change with GFCI on the old circuits sounds like your best bet.
i've put GFCI devices in to replace individual devices, with no daisy chaining,
but old, small boxes don't work well for that.

note: good luck with bending that old wire around with a service change.....
better you, than me...... :p
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
In fact, IMO, 406.4(D)(1) guides one to use the existing EGC of Type AC cable armor to provide for grounding-type receptacles.
In fact?

Is that not a point of contention with many of us?
That it is contentious to so many, here, is really amazing to me, in relationship to the written Code. There are those of us who have flatly stated that BX was never an equipment grounding conductor, which is wrong, period.

2014 NEC 250.118(8) defines EGC as the "armor of Type AC armored cable," armored cable which has been installed as required by the 1913 NEC and all later editions. This is not my opinion. Type AC is in print in all NECs from the 1913 NEC until today, as the type of armored cable required by Article 320. With or without a metal bonding strip all the armored cable is Type AC. Every edition of the NEC from the 1913 NEC on has said the armor is a grounding means, and, later, when the term was defined, an equipment grounding conductor.

The Code says the receptacle outlet (where the wiring method is Article 320 Armored Cable Type AC) HAS an EGC, therefore, 406.4(D)(1) requires that a replacement receptacle be of the grounding-type. That's Code.

That said, when I go to a Premises and work on the wiring, I first examine its condition and integrity. If the installation has "worn out", or has been deteriorated by heat, water, UV light, ozone, or bad workmanship / maintenance, then one acts accordingly and repairs or replaces as necessary; . . . but, just because I can remember seeing such and such a bad condition on another installation doesn't automatically mean this Premises Article 320 wiring HAS to be so afflicted, as well.
 

tkb

Senior Member
Location
MA
If the AC (BX) cable has a bonding strip and the connectors were listed for the AC cable, I would not recommend replacing just because I don't prefer AC cable.

There is absolutely no reason to replace unless the conductor insulation is deteriorating. I have seen where the exposed conductors are bad, but when the jacket is stripped back the wires are like new, even with the old cloth covered conductors.
 

iwire

Moderator
Staff member
Location
Massachusetts
That it is contentious to so many, here, is really amazing to me, in relationship to the written Code. There are those of us who have flatly stated that BX was never an equipment grounding conductor, which is wrong, period.

2014 NEC 250.118(8) defines EGC as the "armor of Type AC armored cable," armored cable which has been installed as required by the 1913 NEC and all later editions. This is not my opinion. Type AC is in print in all NECs from the 1913 NEC until today, as the type of armored cable required by Article 320. With or without a metal bonding strip all the armored cable is Type AC. Every edition of the NEC from the 1913 NEC on has said the armor is a grounding means, and, later, when the term was defined, an equipment grounding conductor.

The Code says the receptacle outlet (where the wiring method is Article 320 Armored Cable Type AC) HAS an EGC, therefore, 406.4(D)(1) requires that a replacement receptacle be of the grounding-type. That's Code.

That said, when I go to a Premises and work on the wiring, I first examine its condition and integrity. If the installation has "worn out", or has been deteriorated by heat, water, UV light, ozone, or bad workmanship / maintenance, then one acts accordingly and repairs or replaces as necessary; . . . but, just because I can remember seeing such and such a bad condition on another installation doesn't automatically mean this Premises Article 320 wiring HAS to be so afflicted, as well.
Al, we went through this, it is not an EGC under current code regardless of it being one in the past.
 

rambojoe

Senior Member
Location
phoenix az
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...
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
. . . it is not an EGC under current code regardless of it being one in the past.
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.
 
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