BX as a ground.

[Netpog]

... I seem to remember numbers as high as 3 ohms per 100 feet for a jacket with no bonding strip.

That's pretty much what I measured as the ground resistance in my BX branch circuits. Maybe a little higher.

 

[mbrooke]

And now we have the Peter D Electrical Code.

Or a man who knows reality :thumbsup:


I read in this thread 3 ohms per 100 feet... so that would be 40amps. This of course assumes all the terminations of the armor are good.

 

[romex jockey]

So what say the good book?

250.118 .8>

(8) Armor of Type AC cable as provided in 320.108

320.108 Equipment Grounding Conductor. Type AC
cable shall provide an adequate path for fault current as
required by 250.4(A)(5) or (B)(4) to act as an equipment
grounding conductor.

250.4(A)(5) Effective Ground-Fault Current Path. Electrical
equipment and wiring and other electrically conductive ma-
terial likely to become energized shall be installed in a
manner that creates a low-impedance circuit facilitating the
operation of the overcurrent device or ground detector for
high-impedance grounded systems. It shall be capable of
safely carrying the maximum ground-fault current likely to
be imposed on it from any point on the wiring system
where a ground fault may occur to the electrical supply
source. The earth shall not be considered as an effective
ground-fault current path.

seems 3 ohms per 100 is a isn't a qualifier here, unless one is installing 250kcmil BX.....

BUT, we've a '14 change in 250.130(C)(4) {thx Dave}.....

250.130(C)(4) Nongrounding Receptacle Replacement or Branch
Circuit Extensions.

(4) An· equipment grounding conductor that is part of an-
other branch circuit that originates from the enclosure
where the branch circuit for the receptacle or branch
circuit originates

I'll skip debates of #12CU flying from box to box trying to be compliant.....

Because it seems 406.4(D) requirements prevail...

406(D) Replacements. Replacement of receptacles shall com-
ply 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.

further reading reveals what appears to be another '14 EX>

406.4(C)(3)Exception: Where replacement of the receptacle type is
impracticable, such as where the outlet box size will not
permit the installation of the GFCI receptacle, the recep-
tacle .shall be permitted to be replaced with a new recep-
tacle of the· existing .. type:, where GFCI protection is pro-
vided and the receptacle is marked "GFCI protected" and
"no equipment ground," in accordance with 406.4(D)(2)
(a)j . (b),or( c).

Obviously there's been enough 'hammer butting' of gfci's into woefully overfilled older wiring methods....

BUT WAIT .......

406.4(3) states>

(3) A receptacle protected by a listed combination type
arc-fault circuit-interrupter type circuit breaker

Which means for the $ of grounded TP duplex receptacle outlets , plate stickers and one of these , Upgraded BX is compliant....>

~RJ~

 

[iwire]

So what say the good book?

250.118 .8>

(8) Armor of Type AC cable as provided in 320.108

You are trying to apply current code to old wiring methods it can't be done.

 

[romex jockey]

You are trying to apply current code to old wiring methods it can't be done.

Ok, with respect to retrofitting , what would be your advice then?

~RJ~

 

[peter d]

And now we have the Peter D Electrical Code.

So you're going to tell me with a straight face you trust unbonded armored cable as a reliable EGC?

 

[peter d]

Ok, with respect to retrofitting , what would be your advice then?

~RJ~

Treat the system as ungrounded.

 

[romex jockey]

So you're going to tell me with a straight face you trust unbonded armored cable as a reliable EGC?

The HI's plug these in, the lights go blinky blinky, and it's okey dokey Pete....

~R :lol: J~

 

[peter d]

The HI's plug these in, the lights go blinky blinky, and it's okey dokey Pete....

I couldn't possibly care less what HI's do. The question was what do we as professional electricians do about old unbonded BX systems. Unbonded armor is not a recognized EGC, and rightfully so as the impedance is far too high to make a reliable fault path.

 

[infinity]

I couldn't possibly care less what HI's do. The question was what do we as professional electricians do about old unbonded BX systems. Unbonded armor is not a recognized EGC, and rightfully so as the impedance is far too high to make a reliable fault path.

As Al stated although a 90 year old AC cable may be a lousy EGC it was permitted to be used for grounding when it was installed so what section of the NEC would require it to be removed or not used as such?

 

[peter d]

As Al stated although a 90 year old AC cable may be a lousy EGC it was permitted to be used for grounding when it was installed so what section of the NEC would require it to be removed or not used as such?

Your question makes no sense. Let's say I have an old home that is wired with BX and has 2-wire receptacles. I have a choice between replacing the old ones with 2-wire or using 3-wire receptacles because I supposedly have an EGC via the BX. I look in the NEC and I don't see unbonded armored cable listed as an EGC. Therefore my only choice is to use 2-wire receptacles.

As far as it being removed, of course there is no NEC section that requires it to be removed. But there are times when old BX has to be modified or otherwise extended with modern wiring methods. Again, in those cases, we cannot use the unbonded armor as the EGC.

But hey, if you guys want to trust that stuff, be my guest. I've chosen not to take that chance.

 

[romex jockey]

As Al stated although a 90 year old AC cable may be a lousy EGC it was permitted to be used for grounding when it was installed so what section of the NEC would require it to be removed or not used as such?

That would be 250.4(A)(5) Effective Ground-Fault Current Path

How is this verified would be the Q?

Perhaps 590.6-(B)(2) Assured Equipment Grounding Conductor Pro-
gram could be reworded ?


Btw~ note the 406.4(C) ref. .....


~RJ~

 

[romex jockey]

As far as it being removed, of course there is no NEC section that requires it to be removed. .

Curiously enough the insurance cabal has condemned K&T , insulation or no insulation, simply on terms of age alone.

Of interest here is that they'll not address BX at all, even though some of the more savvy ahj's here view it as the greater hazard.

So imagine yourself contracting the removal of all K&T , and leaving the BX

That IS a real world scenario btw, so how to create code compliance would be the bid winning Q

~RJ~

 

[Gene B]

I think installing ground fault protection is a good plan. You don't need an ultra low impedance equipment ground in that case. 0.005A versus 150A...

 

[peter d]

I think installing ground fault protection is a good plan. You don't need an ultra low impedance equipment ground in that case. 0.005A versus 150A...

Good point, short of a total rewire, GFCI protection is a great idea for old BX.

 

[mbrooke]

Good point, short of a total rewire, GFCI protection is a great idea for old BX.

BPH says AFCIs work also :thumbsup:

 

[peter d]

BPH says AFCIs work also :thumbsup:

I believe his words as far as I can throw him. :happyno::happyno:

 

[romex jockey]

Actually ,wouldn't the lower mag trip compliment a high R egc....? ~RJ~

 

[Netpog]

We pause now for jargon clarification.

We pause now for jargon clarification.

[...] 90 year old AC cable may be a lousy EGC [...]

For the benefit of anyone following this thread who's not familiar with the jargon, or with the conflict between casual talk and strict NEC usage...

Article 320 AC cable, introduced around 1959, includes a bonding wire, aka drain wire, so that its metal jacket is listed and NEC-acceptable for use as an Equipment Grounding Conductor.

The 80-90 year old BX we're discussing, like modern Article 330 MC, has a jacket that is no longer an acceptable EGC.

Casually, "AC" might be used to include old BX, or to MC. And some folk use "BX" to refer to modern AC or MC. But for NEC, or GEC, purposes, they are quite distinct.

Historian Al, how'd I do?

 

[peter d]

For the benefit of anyone following this thread who's not familiar with the jargon, or with the conflict between casual talk and strict NEC usage...

Article 320 AC cable, introduced around 1959, includes a bonding wire, aka drain wire, so that its metal jacket is listed and NEC-acceptable for use as an Equipment Grounding Conductor.

The 80-90 year old BX we're discussing, like modern Article 330 MC, has a jacket that is no longer an acceptable EGC.

Casually, "AC" might be used to include old BX, or to MC. And some folk use "BX" to refer to modern AC or MC. But for NEC, or GEC, purposes, they are quite distinct.

Historian Al, how'd I do?

This is why I go to great lengths to describe it as "unbonded BX". I assume that AC cable is understood to have the bonding conductor.