Bx Cable (AC)

[Dennis Alwon]

If you come across 12/2 BX cable that doesn't have that steel wire then we know it cannot be used as a ground. However, it is inherently already grounded and can carry a fault. The code will not allow us to use the cable as a grounding conductor. If I install a gfci and then install receptacles with a ground then am I not, inherently, using the ground?

The ground on the receptacle is connected thru the screws that attach the receptacle to the box and then to the cable. Indirectly are we creating a hazard by allowing 3 wire receptacles on a BX cable without the inner steel wire?

 

[infinity]

If you come across 12/2 BX cable that doesn't have that steel wire then we know it cannot be used as a ground.

There's some debate about this because when the cable was manufactured wasn't the outer jacket considered an EGC just like FMC in lengths greater than 6'. That muddies the water when you want to install a 3-wire receptacle because the NEC is silent on the issue. The GFCI protection with the 3-wire receptacle should be fine and is not prohibited by the NEC.

Personally I think that the problem of the AC overheating during a fault is possible but it is somewhat overblown. Yes it can happen but around here there are thousands of old homes that all have this type of cable still in use. I haven't seen any evidence to show that they're rapidly going up in flames.

 

[LarryFine]

The GFCI protection with the 3-wire receptacle should be fine and is not prohibited by the NEC.

But, interconnecting the EGC terminals of such GFCI-protected receptacles is.

 

[infinity]

But, interconnecting the EGC terminals of such GFCI-protected receptacles is.

There is no wire type EGC in Dennis' example so there is no connection other than the mounting screws connecting the receptacle to the metal box which is connected to the armor.

 

[rambojoe]

The gfi will know the differance between the yoke connected (according to you) to bonded jacket and the actuall ground term...
Will not work- definately will not work w/a gfi recept tester unless you do silly things...

 

[infinity]

Will not work- definately will not work w/a gfi recept tester unless you do silly things...

Why wouldn't it work? The GFCI receptacle IS actually grounded through the cable armor. The question is since that cable armor is no longer an acceptable EGC is it code compliant to install the 3-wire receptacle?

 

[Little Bill]

The gfi will know the differance between the yoke connected (according to you) to bonded jacket and the actuall ground term...
Will not work- definately will not work w/a gfi recept tester unless you do silly things...

A GFCI doesn't know, or care, if there is an EGC connected. It works off of any imbalance between hot and neutral current.

 

[infinity]

A GFCI doesn't know, or care, if there is an EGC connected. It works off of any imbalance between hot and neutral current.

I think that Joe was commenting about using a receptacle tester which simulates the imbalance by sending it to the EGC.

 

[augie47]

I think it's important to point out to the owners of property with the old steel BX can be a fire hazard as the jacket can heat to a dangerous level when it carries a ground fault.

 

[Little Bill]

I think that Joe was commenting about using a receptacle tester which simulates the imbalance by sending it to the EGC.

I was responding to his first sentence.

The gfi will know the differance between the yoke connected (according to you) to bonded jacket and the actuall ground term...

 

[rambojoe]

A GFCI doesn't know, or care, if there is an EGC connected. It works off of any imbalance between hot and neutral current.

Reread my post...
I will leave it to dennis to try.

 

[rambojoe]

If memory serves (gasp) it wont reset.