We have some BX runs laid out in a "star" (or spoke-and-hub)
configuration in our basement.

The electrician suggested replacing the old BX with Romex since he
said that the BX relies on the cladding for grounding which can rust
leaving the circuits ungrounded.

Is this a real concern with BX?
Is Romex better than old BX or does the metal cladding give you a
better quality cable?

There has always been debating regarding that. IMHO, I'd say the grounding
of a copper wire is better than the sheath of rusty steel, but on the other
hand, the steel affords better physical protection. The insulating
properties of the wire inside is more important and any new cable nm or ac
(romex or bx) would be better than an old cable
"blueman" wrote in message
...
We have some BX runs laid out in a "star" (or spoke-and-hub)
configuration in our basement.

The electrician suggested replacing the old BX with Romex since he
said that the BX relies on the cladding for grounding which can rust
leaving the circuits ungrounded.

Is this a real concern with BX?
Is Romex better than old BX or does the metal cladding give you a
better quality cable?

On Tue, 18 Jan 2005 00:22:41 GMT, blueman wrote:

We have some BX runs laid out in a "star" (or spoke-and-hub)
configuration in our basement.

The electrician suggested replacing the old BX with Romex since he
said that the BX relies on the cladding for grounding which can rust
leaving the circuits ungrounded.

imho:

If it aint broke dont fix. Just keep an eye on it. If it rusts, you
have another problem, tackle the humidity issue asap.


Is this a real concern with BX?
Is Romex better than old BX or does the metal cladding give you a
better quality cable?

Personally I like the dedicated equipment grounding conductor, but
then I have to remind myself, BX(AC) has a dedicated equipment
grounding conductor, and unlike romex(NM) it also shields the
conductors from accidental abuse.

What is the condition of the cladding now?

OH, btw, don't let anyone unnessarly touch the cables. I bet
electrician is handling them alot. The oils and salts on your hands
will attract moisture and discolor(and possibly corrode) the cladding.
Make it look like it needs replaceing.

BTW, I''ve been in houses that were in crappy conditions structurally,
but the BX (AC) was going strong.

later,

tom @ www.FindMeShelter.com

You can bang a nail thru Romex a whole lot easier than you can BX .

wrote:


Personally I like the dedicated equipment grounding conductor, but
then I have to remind myself, BX(AC) has a dedicated equipment
grounding conductor, and unlike romex(NM) it also shields the
conductors from accidental abuse.

BX isn't AC. BX doesn't have the grounding conductor, which means it
acts like an inductor when the cladding is used as a conductor. This is
why the bare grounding conductor was added, and the name changed to AC.

This has been discussed here many times.

John Hines wrote:

wrote:

Personally I like the dedicated equipment grounding conductor, but
then I have to remind myself, BX(AC) has a dedicated equipment
grounding conductor, and unlike romex(NM) it also shields the
conductors from accidental abuse.

BX isn't AC.

The modern AC is repeatedly referred to as BX by electricians and
electrical supply stores. I was in HD a couple of days ago and they
had a special on 250ft 12/3 ***BX***. DIY books seem to use the BX
designation more frequently than AC. Like Romex and Kleenex and Xerox,
BX was a trade name used by the inventors, GE, and referred to the
location of the plant where it was invented: the Bronx, i.e. BX.
Similarly Romex was invented (!) in Rome NY, hence the name.

BX doesn't have the grounding conductor, which means it
acts like an inductor when the cladding is used as a conductor. This is
why the bare grounding conductor was added, and the name changed to AC.

This has been discussed here many times.

To which discussions you obviously didn't pay attention. The
discussion of induced current in the spiral sheathing resulted in the
conclusion that at 60hz any induced current is infinitesimal. In
present day AC the small gauge follower wire is not the ECG and is
electrically not connected to anything except the outside sheathing.
The outside sheathing IS the ECG.

Although it's difficult to find out the exact history the consensus
seems to be that BX was introduced not primarily to prevent damage to
the conductors from nails and the like but to stop rodents gnawing on
them. The ability to use the outside sheathing as a ground was simply
serendipitous.

As to where the "induction" idea came from I heard an interesting
comment from an old guy who was certainly around at the time of the
introduction of the follower wire (early sixties). He said that the
problem with the old no-follower-wire BX was that it caused
interference with the TV sets which were becoming popular at the time.
The solution was the follower wire which stopped the spiral from
becoming an antenna. This may of course be a crock-of-****. If anyone
has any firm documented information from the era, I'd be interested in
hearing about it.

On Tue, 18 Jan 2005 06:51:04 GMT, SpamFree
wrote:

John Hines wrote:

wrote:

Personally I like the dedicated equipment grounding conductor, but
then I have to remind myself, BX(AC) has a dedicated equipment
grounding conductor, and unlike romex(NM) it also shields the
conductors from accidental abuse.

BX isn't AC.

The modern AC is repeatedly referred to as BX by electricians and
electrical supply stores. I was in HD a couple of days ago and they
had a special on 250ft 12/3 ***BX***. DIY books seem to use the BX
designation more frequently than AC. Like Romex and Kleenex and Xerox,
BX was a trade name used by the inventors, GE, and referred to the
location of the plant where it was invented: the Bronx, i.e. BX.
Similarly Romex was invented (!) in Rome NY, hence the name.

BX doesn't have the grounding conductor, which means it
acts like an inductor when the cladding is used as a conductor. This is
why the bare grounding conductor was added, and the name changed to AC.

This has been discussed here many times.

To which discussions you obviously didn't pay attention. The
discussion of induced current in the spiral sheathing resulted in the
conclusion that at 60hz any induced current is infinitesimal. In
present day AC the small gauge follower wire is not the ECG and is
electrically not connected to anything except the outside sheathing.
The outside sheathing IS the ECG.

Although it's difficult to find out the exact history the consensus
seems to be that BX was introduced not primarily to prevent damage to
the conductors from nails and the like but to stop rodents gnawing on
them. The ability to use the outside sheathing as a ground was simply
serendipitous.

As to where the "induction" idea came from I heard an interesting
comment from an old guy who was certainly around at the time of the
introduction of the follower wire (early sixties). He said that the
problem with the old no-follower-wire BX was that it caused
interference with the TV sets which were becoming popular at the time.
The solution was the follower wire which stopped the spiral from
becoming an antenna. This may of course be a crock-of-****. If anyone
has any firm documented information from the era, I'd be interested in
hearing about it.


Not picking on you, or proclaiming an expert, but if the bonding wire
prevented the clading from being sometype of interferring antena,
wouldn't MC have the same type bonding wire?

Just tossing that out for thought.

later,

tom @ www.ChopURL.com

wrote:

On Tue, 18 Jan 2005 06:51:04 GMT, SpamFree
wrote:

As to where the "induction" idea came from I heard an interesting
comment from an old guy who was certainly around at the time of the
introduction of the follower wire (early sixties). He said that the
problem with the old no-follower-wire BX was that it caused
interference with the TV sets which were becoming popular at the time.
The solution was the follower wire which stopped the spiral from
becoming an antenna. This may of course be a crock-of-****. If anyone
has any firm documented information from the era, I'd be interested in
hearing about it.

Not picking on you, or proclaiming an expert, but if the bonding wire
prevented the clading from being sometype of interferring antena,
wouldn't MC have the same type bonding wire?

Just tossing that out for thought.

Like I said this might be a crock-of-****; it just seemed to be an
interesting hypothesis given the apparent problems with the induced
resistance mantra. I can only guess (and the physics are way beyond my
level) that perhaps the interference only occurs when the EGC (outside
sheathing) is carrying current (i.e. there is some sort of fault).
With MC the armor never carries current even if a fault occurs. This
would also explain why there's no rush to replace the installed
no-follower-wire AC: the armor has to be used as an EGC AND a fault
has to occur.

SpamFree wrote:
John Hines wrote:


wrote:


Personally I like the dedicated equipment grounding conductor, but
then I have to remind myself, BX(AC) has a dedicated equipment
grounding conductor, and unlike romex(NM) it also shields the
conductors from accidental abuse.


BX isn't AC.


The modern AC is repeatedly referred to as BX by electricians and
electrical supply stores. I was in HD a couple of days ago and they
had a special on 250ft 12/3 ***BX***. DIY books seem to use the BX
designation more frequently than AC. Like Romex and Kleenex and Xerox,
BX was a trade name used by the inventors, GE, and referred to the
location of the plant where it was invented: the Bronx, i.e. BX.
Similarly Romex was invented (!) in Rome NY, hence the name.


BX doesn't have the grounding conductor, which means it
acts like an inductor when the cladding is used as a conductor. This is
why the bare grounding conductor was added, and the name changed to AC.


This has been discussed here many times.


To which discussions you obviously didn't pay attention. The
discussion of induced current in the spiral sheathing resulted in the
conclusion that at 60hz any induced current is infinitesimal. In
present day AC the small gauge follower wire is not the ECG and is
electrically not connected to anything except the outside sheathing.
The outside sheathing IS the ECG.

Although it's difficult to find out the exact history the consensus
seems to be that BX was introduced not primarily to prevent damage to
the conductors from nails and the like but to stop rodents gnawing on
them. The ability to use the outside sheathing as a ground was simply
serendipitous.

As to where the "induction" idea came from I heard an interesting
comment from an old guy who was certainly around at the time of the
introduction of the follower wire (early sixties). He said that the
problem with the old no-follower-wire BX was that it caused
interference with the TV sets which were becoming popular at the time.
The solution was the follower wire which stopped the spiral from
becoming an antenna. This may of course be a crock-of-****. If anyone
has any firm documented information from the era, I'd be interested in
hearing about it.

Underwriters Laboratories conducted test back in the sixties on the use
of the armor of metal jacketed cable as an Equipment Grounding Conductor
(EGC). The results of that testing revealed that the spiral wound
metallic tape armor was unsuitable for use as an EGC unless the spirals
were shorted to each other by an internal bonding strip. Even on newly
manufactured cable the absence of a bonding strip more than tripled the
time to open of some Over Current Protective Devices (OCPD). The effect
this had was to allow an arcing fault to continue long enough to result
in the ignition of combustible structural elements. The UL report led
to the requirement for a bonding strip inside the armor of cable
assemblies were the armor would serve as the EGC for the circuit. The
accelerated aging tests showed that the problem was much worse in cables
that had time to develop a layer of corrosion between the spirals and
that it happened well before the corrosion was visible to the naked eye.
I have attended fires that were caused by the failure of older "BX"
cable to conduct enough fault current to trip the OCPD prior to ignition.

Several posters have said here that impedance or rather the reactive
component of the total impedance could not possibly make a difference at
60 hertz. I don't know how to explain away the testing that was done by
UL that showed that a wireman's failure to cut a slot between two
knockouts of a metal box that each pass a conductor of an AC circuit
into that box will result in inductive heating and that this inductive
heating can, over time, cause the pyrolysis of the supporting structural
element to which such a box is attached resulting in the eventual open
flaming ignition of the structure. That process takes months rather
than hours so it is not well understood in the industry because the
effect is not readily discernible over a short time.

I do not lay any claim to fully understanding the physics involved and
according to some posters that makes me a "codebot." If my
unwillingness to agree with the newsgroup's self appointed experts over
the work of UL and the National Fire Protection Association makes me a
"codebot" then I will except that more readily then the task of carrying
out the dead from fires of electrical origin. I guess that means that
"codebots" don't think they know all there is to know about electrical
safety and are willing to depend on the professional judgment of the
engineers at UL and NFPA more readily than the "experts" here.
--
Tom H

On Tue, 18 Jan 2005 15:27:48 GMT, HorneTD
wrote:

SpamFree wrote:
John Hines wrote:


wrote:


Personally I like the dedicated equipment grounding conductor, but
then I have to remind myself, BX(AC) has a dedicated equipment
grounding conductor, and unlike romex(NM) it also shields the
conductors from accidental abuse.


BX isn't AC.


The modern AC is repeatedly referred to as BX by electricians and
electrical supply stores. I was in HD a couple of days ago and they
had a special on 250ft 12/3 ***BX***. DIY books seem to use the BX
designation more frequently than AC. Like Romex and Kleenex and Xerox,
BX was a trade name used by the inventors, GE, and referred to the
location of the plant where it was invented: the Bronx, i.e. BX.
Similarly Romex was invented (!) in Rome NY, hence the name.


BX doesn't have the grounding conductor, which means it
acts like an inductor when the cladding is used as a conductor. This is
why the bare grounding conductor was added, and the name changed to AC.


This has been discussed here many times.


To which discussions you obviously didn't pay attention. The
discussion of induced current in the spiral sheathing resulted in the
conclusion that at 60hz any induced current is infinitesimal. In
present day AC the small gauge follower wire is not the ECG and is
electrically not connected to anything except the outside sheathing.
The outside sheathing IS the ECG.

Although it's difficult to find out the exact history the consensus
seems to be that BX was introduced not primarily to prevent damage to
the conductors from nails and the like but to stop rodents gnawing on
them. The ability to use the outside sheathing as a ground was simply
serendipitous.

As to where the "induction" idea came from I heard an interesting
comment from an old guy who was certainly around at the time of the
introduction of the follower wire (early sixties). He said that the
problem with the old no-follower-wire BX was that it caused
interference with the TV sets which were becoming popular at the time.
The solution was the follower wire which stopped the spiral from
becoming an antenna. This may of course be a crock-of-****. If anyone
has any firm documented information from the era, I'd be interested in
hearing about it.

Underwriters Laboratories conducted test back in the sixties on the use
of the armor of metal jacketed cable as an Equipment Grounding Conductor
(EGC). The results of that testing revealed that the spiral wound
metallic tape armor was unsuitable for use as an EGC unless the spirals
were shorted to each other by an internal bonding strip. Even on newly
manufactured cable the absence of a bonding strip more than tripled the
time to open of some Over Current Protective Devices (OCPD). The effect
this had was to allow an arcing fault to continue long enough to result
in the ignition of combustible structural elements. The UL report led
to the requirement for a bonding strip inside the armor of cable
assemblies were the armor would serve as the EGC for the circuit. The
accelerated aging tests showed that the problem was much worse in cables
that had time to develop a layer of corrosion between the spirals and
that it happened well before the corrosion was visible to the naked eye.
I have attended fires that were caused by the failure of older "BX"
cable to conduct enough fault current to trip the OCPD prior to ignition.

Several posters have said here that impedance or rather the reactive
component of the total impedance could not possibly make a difference at
60 hertz. I don't know how to explain away the testing that was done by
UL that showed that a wireman's failure to cut a slot between two
knockouts of a metal box that each pass a conductor of an AC circuit

This is because the conductors are seperated. If they are together,
they kinda cancel out their magentic fluxes, reducint inductive
heating. I think that's why it's not much of a concern in bundled
conductors, and even code requires same circuit conductors to be
organized together.


into that box will result in inductive heating and that this inductive
heating can, over time, cause the pyrolysis of the supporting structural
element to which such a box is attached resulting in the eventual open
flaming ignition of the structure. That process takes months rather
than hours so it is not well understood in the industry because the
effect is not readily discernible over a short time.

I do not lay any claim to fully understanding the physics involved and
according to some posters that makes me a "codebot." If my
unwillingness to agree with the newsgroup's self appointed experts over
the work of UL and the National Fire Protection Association makes me a
"codebot" then I will except that more readily then the task of carrying
out the dead from fires of electrical origin. I guess that means that
"codebots" don't think they know all there is to know about electrical
safety and are willing to depend on the professional judgment of the
engineers at UL and NFPA more readily than the "experts" here.

Same here, the code is very indepte, and sometimes not knowing the
history behind a decision, or why a group think, leaves the reader
confused.

Just learning too.....

later,

tom @ www.BookmarkAdmin.com

HorneTD wrote:

I have attended fires that were caused by the failure of older "BX"
cable to conduct enough fault current to trip the OCPD prior to ignition.

I made the point of the difference, since people here working on older
houses can encounter the older BX, and we can not see what is really
happening at their end. I'm not expecting to change the lingo of every
electrician in the world.

Thanks for the post with the details.

According to HorneTD :

Several posters have said here that impedance or rather the reactive
component of the total impedance could not possibly make a difference at
60 hertz.

I was involved in that discussion, and as you may recall, I agreed
_completely_ with you over considering cable armor alone as
"adequate grounding".

The only point where I disagreed with you is the suggestion that
the "coil reactive impedance" is likely to play a significant factor
between tripping the OCPD and not tripping the OCPD. Corrosion is
going to be the main factor in virtually every real world case if
you're dealing with a mere 60Hz.

At 400Mhz, on the other hand, a couple turns of wire is essentially
an open circuit.

I don't know how to explain away the testing that was done by
UL that showed that a wireman's failure to cut a slot between two
knockouts of a metal box that each pass a conductor of an AC circuit
into that box will result in inductive heating and that this inductive

Remember that inductive heating isn't the same thing at all as
reactive impedance. So one doesn't imply the other and v-v.

heating can, over time, cause the pyrolysis of the supporting structural
element to which such a box is attached resulting in the eventual open
flaming ignition of the structure. That process takes months rather
than hours so it is not well understood in the industry because the
effect is not readily discernible over a short time.

I'd love to see this test report. What current level/voltage
was that at?

In order for this to occur at anything remotely resembling the
power/frequency levels that occur in people's homes, there'd have to be
some pretty subtle metalurgical changes going on in the metal box.

There ain't no way that 15A at 60hz going through separate holes in,
say, 16ga steel is going to induce enough current flow to generate
appreciable heat in said steel. No matter how long you waited.
Unless you had the whole assembly in a dewar flask and didn't mind
waiting the months for micro-degree daily increments to get to dangerous
levels.

Indeed, inductive heating _still_ occurs _even if_ the whole circuit
goes through one hole. Thus, the same thing would happen (albeit take
longer) even if the whole cable went through one hole.

Unbalanced circuits (eg: hot plus neutral) radiate, period. Thus
they induce current in surrounding plate penetration, one or two hole.
Thus they generate heat.

But, the frequency is VERY important.

The amount of inductive heating at 60hz on simple plate penetration
is small. Not non-existant, but _extremely_ small. So small to be
dwarfed by conduction/convection in any real-world situation we're
likely to see. Now, if we're talking million amp plus flows, that's
different.

I do not lay any claim to fully understanding the physics involved and
according to some posters that makes me a "codebot."

I'm not one of those posters. I consider you a highly skilled and
knowledgeable professional, with very valuable real experience. Just
don't know RF very well - s'alright, you know a _lot_ more about code
than I do.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

HorneTD wrote:

SpamFree wrote:

Underwriters Laboratories conducted test back in the sixties on the use
of the armor of metal jacketed cable as an Equipment Grounding Conductor
(EGC). The results of that testing revealed that the spiral wound
metallic tape armor was unsuitable for use as an EGC unless the spirals
were shorted to each other by an internal bonding strip. Even on newly
manufactured cable the absence of a bonding strip more than tripled the
time to open of some Over Current Protective Devices (OCPD). The effect
this had was to allow an arcing fault to continue long enough to result
in the ignition of combustible structural elements. The UL report led
to the requirement for a bonding strip inside the armor of cable
assemblies were the armor would serve as the EGC for the circuit. The
accelerated aging tests showed that the problem was much worse in cables
that had time to develop a layer of corrosion between the spirals and
that it happened well before the corrosion was visible to the naked eye.
I have attended fires that were caused by the failure of older "BX"
cable to conduct enough fault current to trip the OCPD prior to ignition.

Several posters have said here that impedance or rather the reactive
component of the total impedance could not possibly make a difference at
60 hertz. I don't know how to explain away the testing that was done by
UL that showed that a wireman's failure to cut a slot between two
knockouts of a metal box that each pass a conductor of an AC circuit
into that box will result in inductive heating and that this inductive
heating can, over time, cause the pyrolysis of the supporting structural
element to which such a box is attached resulting in the eventual open
flaming ignition of the structure. That process takes months rather
than hours so it is not well understood in the industry because the
effect is not readily discernible over a short time.

I do not lay any claim to fully understanding the physics involved and
according to some posters that makes me a "codebot." If my
unwillingness to agree with the newsgroup's self appointed experts over
the work of UL and the National Fire Protection Association makes me a
"codebot" then I will except that more readily then the task of carrying
out the dead from fires of electrical origin. I guess that means that
"codebots" don't think they know all there is to know about electrical
safety and are willing to depend on the professional judgment of the
engineers at UL and NFPA more readily than the "experts" here.

"Always question." "Always be wary of asserted authority."

In none of the above do you make reference to anything we can check or
to anything which explains the apparent anomaly of a perfectly good
steel strip connecting the source of the fault with the building
ground not working properly if wound in the form of a spiral but being
OK if a ridiculously small gauge wire follows along the spiral. The
proffered explanation of inductive resistance seems to be definitively
crushed by Chris Lewis who in the earlier discussions was supported by
other posters who had presumably done the same calculations. In any
event no one pointed to errors in his reasoning.

You (or UL) seem to think that the EGC depends on the contact between
each of the spirals. Why? AC is a continuous length of steel that just
happens to be in a spiral form. If one were to pull apart the spirals
thereby extending the steel to its full length and properly connect
both ends wouldn't that form an adequate EGC? Corrosion between the
spirals is really immaterial. The only questions would seem to be: Is
the steel armor of sufficient gauge to carry the current and are the
ends properly connected? In the latter case you can badly connect the
NM ground too and connections can work loose over time so how does
that differ?

And please spare us the drama. "Carrying out the dead" indeed!