BX as a ground.

[mbrooke]

well, the NEC is an evolving document.

sometimes the driving forces are altruistic, sometimes crassly commercial,
and subject to the judgement of the person(s) making the call.

BX, Aluminum Romex, AFCI breakers. all part of the code at one point in time.

unless i'm mistaken, as a group of [professionals] the only thing we can absolutely
agree on, is ground up, or ground down, right?

all two wire ungrounded systems should have the 3 wire grounded receptacle
installed ground UP, so we know it's not to be depended upon... correct?



and when this horse is dead, can we please discuss something less controversial,
like gun control?

We can agree on laws of physics.

 

[user 100]

I have a copy of the 1918 NEC open at the moment, and little time left at the moment. . . my apologies for brevity,

The 1918 NEC grounding means on the armor of armored cable is in place then.

So the NEC was at least concerned about bonding for a longer time than what a lot of us thought.

Thanks for the reference.

 

[GoldDigger]

JMHO: If the sheath of the existing unbonded BX was not used as an EGC as originally installed you cannot change the way it is terminated to now use it as an EGC. If the existing BX armor was terminated at both ends so as to constitute a raceway EGC, then it is code compliant to use that path to connect a three wire receptacle.
But I personally would not do it.

 

[GerryB]

I see the OP has not jumped back in the fray here, I'm sure his is trying to stop his head from spinning. Hey, I wonder if this "vintage" property has a nice Bulldog Pushmatic panel in the basement? Oh oh, no GFI breakers available. O well, since they are gutting the house anyway for the rewire we'll just upgrade the service at the same time. The bank will pay, they got the money. Hey, it's a bank, right!
Don't get me wrong, an informative thread. If the OP decides to buy the house himself, he knows what to do. In the meantime I think the OP will find out that the banks, property managers and the like are only interested in "the bare minimum" to sell the house. So to the OP again, change the receptacles or tell them you're not interested. MHO.

 

[romex jockey]

We can agree on laws of physics.

250.4(A)(5) used to be '2551' 50 years ago

it reads>

Effective Grounding. The path to ground from circuits, equipment, or conductor enclosures shall be permanent and continuous and shall have ample carrying capacity to conduct safely and currents liable to be imposed on it, and shall have impedance sufficiently low to limit the potential above ground ,and to facilitate the operation of the overcurrent devices in the circuit.

What this references is basic ohms law , fairly basic physics , even for the average spark... ~RJ~

 

[Netpog]

I'm reminded that there was once an OP. E54fireman wasn't interested in the bad attitude that some of us (me, peter d, mbrooke) share about already-existing grounded receptacles that were 'bonded' by old BX. He didn't ask whether it might have been NEC-acceptable to use 1930's-vintage BX in the 50's as an EGC, or in the late 1900's to bond a grounded (NEMA 5-15) replacement receptacle.

The question is: given that old BX, can he replace two-prong receptacles with grounded ones? I think this century's NEC is clear that he can't do it. Let's have a look:

250.130 (C) Nongrounding Receptacle Replacement or Branch Circuit. The equipment grounding conductor of a grounding-type receptacle or a branch-circuit extension shall be permitted to be connected to any of the following:
[a bunch of alternatives that ALL require GEC or EGC]

We're not done, of course: In the '50s that BX was a perfectly cromulent EGC. But the 2014 NEC makes its own demands. Looking at the Article 100 definition of EGC:

Grounding Conductor, Equipment (EGC). [...]
Informational Note No.2: See 250.118 for a list of acceptable equipment grounding conductors.

250.118 Types of Equipment Grounding Conductors.
The equipment grounding conductor run with or enclosing the circuit conductors shall be one or more or a combination of the following:
[... blah blah “listed” blah “listed” or maybe “listed”...]

If you're going to replace that receptacle under the current NEC, you need an EGC that's actually listed now. I see nothing in 250.118 that supports your vintage BX as an EGC for that replacement.

It does call out currently-listed AC, and the "MC cable that is listed and identified as an equipment grounding conductor". That's all you get.

In other news, I'm surprised to report that this page will be your only google hit on the phrase "cromulent EGC".

 

[growler]

What you are effectively doing, by claiming that nothing short of total BX replacement should be done, is throw up an economic barrier to those who are maintaining the Premises Wiring (System). They withdraw from repairing worn receptacles because of your opinion. Who's creating the risk?

I don't think Pete is createing a risk, he is only following the NEC.

If the local authorities want to they could grant special permission to use BX as an effective ground but I don't think they would. Why should it be up to the electrician to assume the liability for this?

Who was it that promised people that when they had a house wired in the 1930s that it would last forever anyway? If you had a house built in the 1930's you have probably replaced the roofing system many times, the gutters, the flooring, the plumbing and the heating system but for some reason the electrical system is eternal.


I have worked on old houses that have been remodeled many times and yet I end up replaceing wiring that in old gas pipes.

 

[Netpog]

What you are effectively doing, by claiming that nothing short of total BX replacement should be done, is throw up an economic barrier to those who are maintaining the Premises Wiring (System). They withdraw from repairing worn receptacles because of your opinion. Who's creating the risk?

We're not claiming that. We (and the NEC) are claiming that you should replace it (or run a supplemental EGC) if you want an grounded receptacle.

There are clear alternatives to replacing the BX. GFCI's aren't that expensive. Or you could install new ungrounded receptacles. (Although I'm not sure they make tamper resistant ones.)

 

[romex jockey]

And this thread is just focused on an outlet receptacle

Imagine if the OP wants to change out the lights too....

Creating code compliant BX renovations seems to be evolving to a specialized niche...

~RJ~

 

[peter d]

Remember the OP? This is the question:

To which the first answer was:

That answer is only accurate if the "old BX" is being INSTALLED now in new construction.

Yeah, ok. :roll:

Peter, the question is not about installing new runs of pre-1950s Armored Cable type BX in new installations.

The OP question is about receptacle replacement in an existing dwelling that was originally wired to the Code in effect at the time of its construction with "unbonded" armored cable type BX.

I'm quite aware of the question being asked. And I have stated my case quite clearly - to rely on old BX cable as an EGC is reckless and dangerous, and is an NEC violation. I think it's extremely unprofessional advice to recommend that an electrician can install grounded receptacles on armored cable that can literally heat up and glow red inside of a wall under fault conditions. I suspect you're digging your heels in on this one because you have already done this many times, and want to convince yourself that what you did is safe and fine. Well, I'm here to tell you that it's neither safe nor fine, and you have left fire hazards in many homes as a result.

What you are effectively doing, by claiming that nothing short of total BX replacement should be done, is throw up an economic barrier to those who are maintaining the Premises Wiring (System). They withdraw from repairing worn receptacles because of your opinion. Who's creating the risk?

As I just stated, you are the one who has created the risk by relying on a cable with unacceptably high impedance for an EGC. I'm choosing to err on the side of caution, and treat the entire system as ungrounded. Can you point out where I said it should all be replaced? I stated two cost effective options - use 2-wire receptacles, or the best option is to GFCI protect the entire circuit at the point of origin. As others have stated, a system with this ancient garbage has outlived its useful life and should be replaced if at all possible. Chances are, there are other serious issues with the wiring system that have already been pointed out (crumbling insulation at lighting outlets, loose clamps, undersized boxes, no useable conductor length, rusted cable, inadequate circuitry, etc.)

 

[mbrooke]

250.4(A)(5) used to be '2551' 50 years ago

it reads>



What this references is basic ohms law , fairly basic physics , even for the average spark... ~RJ~

I agree. There is AC impedance, but at the lengths and voltages used in residential wiring ohms law alone gives very accurate real world numbers and can thus be ignored for all practical purposes. However there is one major factor to consider: as most materials increase in temperature its resistive impedance goes go up. So BX with a 4 ohm room temperature jacket will initially pass 30 amps, and while that will eventually trip a 15 amp breaker; come reality as BX armor passes current it heats up and in turn ohms increase. Thus, 4 ohms at room temperature may go to say 6 ohms when heated dropping the initial current to the point the breaker may never trip.

Even if the breaker does trip, there is still this:

and shall have impedance sufficiently low to limit the potential above ground

During that 15, 30 second, 1, 2 minute ect trip there will be major voltage drop across the EGC. On typical circuit lengths a 3 ohm jacket only pulls down the current across the hot conductor by about 10 to 20 volts. So a fault in a refrigerator chassis will cause the frame to rise to 105 volts relative to plumbing and all other grounded equipment in the time it take to trip the breaker which could be up to 90 seconds. If a person is simultaneously in contact with the case and say sink, they can be parallelized between the two. Granted the chance is slim a fridge would energize the exact moment this happens, but picture a drill, treadmill, toaster overn, ect that only livens up when the user switches it to on. In that case squeezing the handle of a faulted drill could injure or even kill someone. Yes the breaker may trip, but after sufficient current for sufficient time has done tissue damage.


Arc flash aside, the more current you can pull across a breaker the better.

 

[mbrooke]

Well, I'm here to tell you that it's neither safe nor fine, and you have left fire hazards in many homes as a result.

Not only fire, but electrocution. Can you imagine the voltage drop (or lack there of) across the EGC?

As I just stated, you are the one who has created the risk by relying on a cable with unacceptably high impedance for an EGC. I'm choosing to err on the side of caution, and treat the entire system as ungrounded. Can you point out where I said it should all be replaced? I stated two cost effective options - use 2-wire receptacles, or the best option is to GFCI protect the entire circuit at the point of origin. As others have stated, a system with this ancient garbage has outlived its useful life and should be replaced if at all possible. Chances are, there are other serious issues with the wiring system that have already been pointed out (crumbling insulation at lighting outlets, loose clamps, undersized boxes, no useable conductor length, rusted cable, inadequate circuitry, etc.)

I agree. Not to mention older versions of the NEC actually mention insulation will eventually fail. (hint hint) The insulation is worse then that on Knob and Tube. Even if the insulation falls of knob and tube inside a wall cavity between ceramic supports, the insulators will usually act as a back up.

When the insulation does fail that BX will either pass current and heat up, or sit energized against wood for years leading to pyrphoric carbonation. Eventually a fire will break out that will be spun into an arc fault rather then restive heating or moisture being driven out of wood via low level current. Fires will continue to happen based on myths while mythical solutions are mandated in order to solve them. No trade magazine or NEMA member will tell you this because it brings people out of the dream world which they have been compelled to believe as reality.

 

[romex jockey]

Being i live in the land time forgot, older wiring is part of my daily service call diet.

We've seen many incidents of 'BX metal jacket heating' , some even appearing as a line of dots through old horsehair plaster....

Then there are the BX/K&T/cloth NM mixes , one never knows if the BX jacket is solid back to the MBJ , or appears so through various avenues [/i](furnace, plumbing, etc....)[/i]


Let's keep in mind the debut of the smaller #16 ecg in cloth nm was not universally accepted either.

It was lamented as a 3rd lethal path by many.....and rightly so...

At the time they didn't know what to do with it due to non grounding metal boxes and devices. This is the era where they either cut them off, or employed the famous Boston Back wrap termination method.

Most of these era methods introduced impedance of whatever ecg was present.

This is where i wish our trade had some sort of historical archivist vs. all these anecdotal(s)....

~RJ~

 

[K8MHZ]

Being i live in the land time forgot, older wiring is part of my daily service call diet.

We've seen many incidents of 'BX metal jacket heating' , some even appearing as a line of dots through old horsehair plaster....

Then there are the BX/K&T/cloth NM mixes , one never knows if the BX jacket is solid back to the MBJ , or appears so through various avenues [/i](furnace, plumbing, etc....)[/i]


Let's keep in mind the debut of the smaller #16 ecg in cloth nm was not universally accepted either.

It was lamented as a 3rd lethal path by many.....and rightly so...

At the time they didn't know what to do with it due to non grounding metal boxes and devices. This is the era where they either cut them off, or employed the famous Boston Back wrap termination method.

Most of these era methods introduced impedance of whatever ecg was present.

This is where i wish our trade had some sort of historical archivist vs. all these anecdotal(s)....

~RJ~

You live in one of those places, too?

Last year we pulled a service out of a 2 unit apartment. It was a 30 amp 120 volt (NOT 120/240) with FOUR fuses in it. 2 in the hot, 2 in the neutral. Two fuses were inside the enclosure, two were on the bottom accessible without opening the door of the enclosure. The sticker from the last inspection was still in the enclosure. It was dated 1919.

The service was working fine. The city inspector gigged it on a rental inspection. It was fed from the meter with 10 AWG wiring.

I kept it, sticker and all. I kind of collect stuff like that we find in these old places.

 

[al hildenbrand]

I'm reminded that there was once an OP. E54fireman wasn't interested in the bad attitude that some of us (me, peter d, mbrooke) share about already-existing grounded receptacles that were 'bonded' by old BX. He didn't ask whether it might have been NEC-acceptable to use 1930's-vintage BX in the 50's as an EGC, or in the late 1900's to bond a grounded (NEMA 5-15) replacement receptacle.

The question is: given that old BX, can he replace two-prong receptacles with grounded ones? I think this century's NEC is clear that he can't do it. Let's have a look:

250.130 (C) Nongrounding Receptacle Replacement or Branch Circuit. The equipment grounding conductor of a grounding-type receptacle or a branch-circuit extension shall be permitted to be connected to any of the following:
[a bunch of alternatives that ALL require GEC or EGC]

We're not done, of course: In the '50s that BX was a perfectly cromulent EGC. But the 2014 NEC makes its own demands. Looking at the Article 100 definition of EGC:

Grounding Conductor, Equipment (EGC). [...]
Informational Note No.2: See 250.118 for a list of acceptable equipment grounding conductors.

250.118 Types of Equipment Grounding Conductors.
The equipment grounding conductor run with or enclosing the circuit conductors shall be one or more or a combination of the following:
[... blah blah “listed” blah “listed” or maybe “listed”...]

If you're going to replace that receptacle under the current NEC, you need an EGC that's actually listed now. I see nothing in 250.118 that supports your vintage BX as an EGC for that replacement.

It does call out currently-listed AC, and the "MC cable that is listed and identified as an equipment grounding conductor". That's all you get.

Thank you, Netpog, for quoting the Code, instead of just giving opinion.

As I have said from the start, with direct citations quoted from the NEC (referenced by clicking on this thread link) :

Old non-bonding-strip BX was a grounding means when installed as part of a complete equipment grounding path.

In using 250.130(C) to substantiate your claim, you have overlooked the first part of that Rule:

VII. Methods of Equipment Grounding

250.130 Equipment Grounding Conductor Connections. Equipment grounding conductor connections at the source of separately derived systems shall be made in accordance with 250.30(A)(1). Equipment grounding conductor connections at service equipment shall be made as indicated in 250.130(A) or (B). For replacement of non–grounding-type receptacles with grounding-type receptacles and for branch circuit extensions only in existing installations that do not have an equipment grounding conductor in the branch circuit, connections shall be permitted as indicated in 250.130(C).

Quoting today's definition of EGC, and failing earlier editions of the NEC that don't use it, is a non-starter. Earlier editions of the NEC clearly state that Armored Cable type BX is a grounding means, just not in today's words.

Now, I, as a field electrician, facing a receptacle outlet that needs its device replaced, can TEST the resistance of the EGC to determine if there is an issue.

 

[mbrooke]

Thank you, Netpog, for quoting the Code, instead of just giving opinion.

Ok, Ive been out on the spot so I guess its the norm for this place... but do you work with BX on a daily basis? From what you say I doubt it. First hand experience is not an opinion, and neither are physics which clearly show what a high impedance EGC will do.

As I have said from the start, with direct citations quoted from the NEC (referenced by clicking on this thread link) :

In using 250.130(C) to substantiate your claim, you have overlooked the first part of that Rule:

I would think the point of that is so new installations are not done in that manner.

Quoting today's definition of EGC, and failing earlier editions of the NEC that don't use it, is a non-starter. Earlier editions of the NEC clearly state that Armored Cable type BX is a grounding means, just not in today's words.

Because they had to withdraw that claim based on what experience taught them latter. Old electrician books advocated testing live wires with fingers. Do we still do that today?

Now, I, as a field electrician, facing a receptacle outlet that needs its device replaced, can TEST the resistance of the EGC to determine if there is an issue.

When you encounter BX, how do you normally do that?

 

[al hildenbrand]

Mbrook, again your words are all opinion. Try some Code.
Tapatalk

 

[mbrooke]

Mbrook, again your words are all opinion. Try some Code.
Tapatalk

So your saying meters are just giving opinions? :lol:


But again, before you nit pick me, how much BX do you work with and how do you perform an ground loop impedance test?

 

[al hildenbrand]

You can't do it, can you?
Tapatalk

 

[mbrooke]

You can't do it, can you?
Tapatalk

It goes both ways. You still have not told me how you perform a loop impedance test.


Personally I think up until this thread you did not know it was an issue and when confronted refuse to reconsider.