BX as a ground.

[e54fireman]

I've been in the trade for a while mostly commercial and just adventured out on my own. running into a few things with some bank owned houses where they are trying to flip them. problem i'm running into is i tell the bank the house has the old bx in there and doesn't have a proper ground needs to be taken out and replaced. They are telling me it's OK just change the outlets and let move on. I've been talking with a few people about this and getting a lot of different answers. so i was wondering can you use the outer casing on bx as a ground while adding self grounding outlets and putting a gfci breaker in at the panel be good. i have guys telling my put a screw to the box and your good, others saying just use self grounding outlets and thats it. looking for some answers as im hoping to land more jobs with this bank.

 

[ActionDave]

If it is the old BX without the bonding strip then the sheathe should not be used as an equipment ground. Look at 250.130(C) and 406.4(D).

 

[JFletcher]

If it is the old BX without the bonding strip then the sheathe should not be used as an equipment ground. Look at 250.130(C) and 406.4(D).

I thought that BX/Greenfield/AC was different than MC in that the outer cover was acceptable as a ground back then???

Installations that were code compliant at the time generally do not need replacing. GFCI breaker/receptacle to 3 prong plugs marked "GFCI protected/no equipment ground" I believe are compliant, as are 2 prong replacements.

 

[ActionDave]

The old BX was dangerous because it would act like a coil and get hot instead of a low impedance path that would blow a fuse that's why they added the bonding strip. Type AC cable is what it is called.

 

[Netpog]

Couldn't you remain compliant by replacing the receptacles with NEMA-1 devices?

Good luck finding TR ones. (In other words, maybe my above suggestion isn't helpful.)

 

[mbrooke]

No bonding strip equals no worky.

 

[infinity]

First, does the AC cable have a bonding strip? If so then the jacket is a listed EGC can can be used as such. If not the jacket was still approved for grounding when it was installed so the question arises can it still be used for that purpose. IMO this is like NM cable with the reduced EGC that was installed years ago.

 

[Netpog]

Rob, I'm pretty sure that by "the old bx" the OP meant vintage pre-AC cable, without bonding strip.

e54fireman, what's the vintage of the house(s) in question?

My 1934 house was wired with the stuff. No EGC anywhere (but plenty of newer NEMA-5 receptacles that would pass the nightlight test, thanks to the lousy high-resistance ground path provided by the spiral armor and the yoke screws). Cloth/rubber insulation that, in the boxless ceiling-luminaire mounts, would crumble to dust if given a hard look. And brutally crowded boxes, with taped splices that are admirable displays of tenacity and craftsmanship. I think those details are pretty typical of this sort of installation.

Also typical: the1970's kitchen rewire, with buried blue boxes, backstabbed devices bonded only through their loose screws, etc.

 

[al hildenbrand]

First, does the AC cable have a bonding strip? If so then the jacket is a listed EGC can can be used as such. If not the jacket was still approved for grounding when it was installed so the question arises can it still be used for that purpose. IMO this is like NM cable with the reduced EGC that was installed years ago.

I agree. Armored cable (old BX) was first developed in the last years of the 1800s. The manufacturing change to include a bonding strip in contact with the jacket didn't occur until the 1950s.

Old non-bonding-strip BX was a grounding means when installed as part of a complete equipment grounding path. The complete grounding path was not always part of its use, as an exception in the Code allowed ungrounded lengths of BX to be used to extend ungrounded wiring methods such as Knob and Tube when adding an outlet or a switch.

You can read some of the Code citations in this earlier post by clicking on this thread link .

 

[Netpog]

Al, that's very interesting! Thanks for the history.

So, was it ever okay to put grounded, NEMA-5, receptacles onto vintage BX?

 

[al hildenbrand]

So, was it ever okay to put grounded, NEMA-5, receptacles onto vintage BX?

Yes.

Before the 1962 NEC requirement that all 120 Volt 15 and 20 Amp receptacles devices be the grounding-type, grounding-type receptacle devices were required in specific locations (somewhat like GFCIs are required in specific locations today). If the branch circuit wiring method was Armored Cable type BX (pre 1950s bonding strip), the BX jacket was the EGC for the grounding-type receptacle.

The metal jacket of BX was NEC allowed as an equipment grounding means.

 

[growler]

I've been in the trade for a while mostly commercial and just adventured out on my own. running into a few things with some bank owned houses where they are trying to flip them. problem i'm running into is i tell the bank the house has the old bx in there and doesn't have a proper ground needs to be taken out and replaced. They are telling me it's OK just change the outlets and let move on. I've been talking with a few people about this and getting a lot of different answers. so i was wondering can you use the outer casing on bx as a ground while adding self grounding outlets and putting a gfci breaker in at the panel be good. i have guys telling my put a screw to the box and your good, others saying just use self grounding outlets and thats it. looking for some answers as im hoping to land more jobs with this bank.

I don't really consider bankers to be experts in electrical. If I were you I would contact the local authorities ( electrical inspector ) and see how they feel about this change out and the use of old BX as ground. I'm thinking they may want these circuits arc fault protected so even if the ground is allowed this job may be a bigger problem than just changing out receptacles.

 

[Pizza]

I agree. Armored cable (old BX) was first developed in the last years of the 1800s. The manufacturing change to include a bonding strip in contact with the jacket didn't occur until the 1950s.

Old non-bonding-strip BX was a grounding means when installed as part of a complete equipment grounding path. The complete grounding path was not always part of its use, as an exception in the Code allowed ungrounded lengths of BX to be used to extend ungrounded wiring methods such as Knob and Tube when adding an outlet or a switch.

You can read some of the Code citations in this earlier post by clicking on this thread link .

Shows you how dumb they were back then.


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[peter d]

My 1934 house was wired with the stuff. No EGC anywhere (but plenty of newer NEMA-5 receptacles that would pass the nightlight test, thanks to the lousy high-resistance ground path provided by the spiral armor and the yoke screws). Cloth/rubber insulation that, in the boxless ceiling-luminaire mounts, would crumble to dust if given a hard look. And brutally crowded boxes, with taped splices that are admirable displays of tenacity and craftsmanship. I think those details are pretty typical of this sort of installation.

Ahh yes, I've rewired and worked on many 1930's BX homes over the years and your description was spot on. The only thing you missed was conductor length was usually 2-3" in those boxes. Unbonded BX was truly evil, it puts K&T and vintage cloth romex to shame. Nothing short of total rewire is the best option for that dangerous stuff, if at all possible.

 

[peter d]

Yes.

Before the 1962 NEC requirement that all 120 Volt 15 and 20 Amp receptacles devices be the grounding-type, grounding-type receptacle devices were required in specific locations (somewhat like GFCIs are required in specific locations today). If the branch circuit wiring method was Armored Cable type BX (pre 1950s bonding strip), the BX jacket was the EGC for the grounding-type receptacle.

The metal jacket of BX was NEC allowed as an equipment grounding means.

Regardless, there's no way in Hades I would every rely on the armor of BX as an adequate EGC. I treat that old BX as an ungrounded system.

 

[Curious nerd]

Someone actually measured the resistance of old BX

Someone actually measured the resistance of old BX

It was part of a program studying the wiring in old houses that were being demolished. I _might_ be able to find the reference. As a practical thing, as opposed to a code thing, I seem to remember numbers as high as 3 ohms per 100 feet for a jacket with no bonding strip.

 

[GerryB]

I've been in the trade for a while mostly commercial and just adventured out on my own. running into a few things with some bank owned houses where they are trying to flip them. problem i'm running into is i tell the bank the house has the old bx in there and doesn't have a proper ground needs to be taken out and replaced. They are telling me it's OK just change the outlets and let move on. I've been talking with a few people about this and getting a lot of different answers. so i was wondering can you use the outer casing on bx as a ground while adding self grounding outlets and putting a gfci breaker in at the panel be good. i have guys telling my put a screw to the box and your good, others saying just use self grounding outlets and thats it. looking for some answers as im hoping to land more jobs with this bank.

If you are hoping to land more jobs with the bank then you will just change the outlets and test that they are grounded. You are not required to do any rewiring, why would you be unless they are opening walls? Why would you put a GFI breaker in?
It's pretty simple I think as I have done many. If You need a permit then you have them understand if the inspector wants something that's what you have to do. If you are only talking about a home inspector or a bank inspector (or even an electrical inspector) I would be comfortable putting in grounded outlets that were grounded through the bx.

 

[al hildenbrand]

Regardless, there's no way in Hades I would every rely on the armor of BX as an adequate EGC. I treat that old BX as an ungrounded system.

And now we have the Peter D Electrical Code.

 

[user 100]

Shows you how dumb they were back then.


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I wouldn't say dumb- just ignorant. They simply didn't know the importance of a low impedance egc- they only cared that it was metal, "decently" conductive and continuous back to the source-nothing more, nothing less. Wait until you come across the #16 or 18 steel separate egc run to few boxes ( ala the older code req's metioned by al hildenbrand above) in older homes that used 2 wire romex.

 

[Netpog]

Al, it's no longer an allowed grounding method, not since 1959, is it? Once we had modern style bonded AC, I gather the BX wasn't appropriate for grounded receptacles, yes?

Ahh yes, I've rewired and worked on many 1930's BX homes over the years and your description was spot on. The only thing you missed was conductor length was usually 2-3" in those boxes.

Yes! Those short conductors were an annoyance, for about a day, before I realized that I was going to replace it all. Every inch.

Unbonded BX was truly evil, it puts K&T and vintage cloth romex to shame. Nothing short of total rewire is the best option for that dangerous stuff, if at all possible.

Thanks for the support. Because that's exactly what I decided: it all had to go. If rather have K&T. At least then your conductors with crumbling insulation aren't snuggled together, wrapped in a toaster wire.