BX jacket used for a ground

[dm9289]

I was reading thru the monthly highlights and one of the threads talked about installing a fan and not having a ground connection but being wired with 2 wire BX cable and it got me to thinking. In my region there is alot of bx some with the extra thin bare wire in it and most without. Primarily what was done with this at receptacles was to ground receptacles to the box utilizing the BX case for a ground. When a home inspector comes with his plug tester it analyzes the plug as correctly wired and grounded and goes on the report as such and apparantly many home flippers have caught on to this.Also when you test with a meter hot to BX case you will get 120v. I was always under the impression that this practice was against code but I could not find a reference for it, does anyone know chapter and verse? More importantly what is the safety hazard in doing this if the case continues to the box properly? What is the danger when the BX case is used and not continuos to the box?

 

[Dennis Alwon]

If the bx cable has the thin metal wire in the casing then it is fine to use the casing as a ground. The problem is with BX without that bare wire.

 

[dm9289]

usually code is made due to a specific danger or loss of life, what danger is there in using regular bx jacket as a ground?

 

[al hildenbrand]

usually code is made due to a specific danger or loss of life, what danger is there in using regular bx jacket as a ground?

Go back to the thread that you reference in your OP and read the very long posts of Mivey's. There are a couple summarizing a 2009 study dealing exactly with the core of your question. There's a lot of good info in those posts.

 

[hurk27]

While it was an accepted ground back when it was first installed, it was found that the connection of the spiral would loose connection over time and instead of acting like one large wire it would act like a much smaller wire but much longer, think of how long it would be if you unwound the spiral, this would increase the impedance and inductance of the fault path.

With that said, it has caused many house fires when a fault would occur, this spiral would heat up like a heating element instead of tripping the breaker.

I have actually seen this once, and scared me half to death trying to get back to the breaker to get it turned off.

The type with the small wire does not have this problem as this small wire acts as a short between the spirals, this small conductor doesn't even have to be terminated as it does it's job just being there against the spirals. By the way, many now call this type "AC" cable which is still a BX type cable which is only a brand name that the cable was called when it was invented.

 

[dm9289]

Thanks to all I get it now, I knew there was a good reason not to do it. After the description of what could happen it reminded me of a furnace coil.

 

[Dilligaf1220]

Old BX cable

Old BX cable

I have seen many times where when replacing BX, the insulation on which the BX was laying had a burn mark. Be careful this could be a problem.
Jim

 

[Dennis Alwon]

Every home in NYC was wired with BX. I don't remember ever seeing it without the bare wire in the BX. We always used it to hold the redheads in place. I am going back 50 years so I am not sure when BX without the bare wire was made or if it was ever used in NYC.

When I did work in Kingston, NY for a contractor who did work at IBM they made us use 12/3 BX strip the red wire and use it as a ground.