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

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.

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.

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!

SpamFree wrote:
HorneTD wrote:
Snip
And please spare us the drama. "Carrying out the dead" indeed!


I have been a volunteer in Fire and Rescue since 1971. In those thirty
three years I have helped to carry out the remains of fourteen persons
who were killed in fires. Three of those persons were killed in fires
of electrical origin and all three of those were pre school aged
children. It strikes me as strange that so many people want to forbid
the fire service from talking about the task of dealing with the burned
bodies of fire victims by accusing us of fear mongering or of being
melodramatic. I'm not dysfunctional from post traumatic stress or
anything even remotely like that but when I talk or write about fire
prevention those people are never far from my mind. I read the
dismissive comments of some posters about the low rate of fire deaths
caused by arcing faults or some other cause and the claims that the
remedy is more expensive then the number of deaths would warrant. Would
you like to make book on whether the parents of those three kids would
agree. I frankly don't care if I subject you to excessive drama as I
believe that is preferable to subjecting anyone to death by fire.
--
Tom H

"HorneTD" wrote in message
. net...
SpamFree wrote:
HorneTD wrote:
Snip
And please spare us the drama. "Carrying out the dead" indeed!

snip
prevention those people are never far from my mind. I read the
dismissive comments of some posters about the low rate of fire deaths
caused by arcing faults or some other cause and the claims that the
remedy is more expensive then the number of deaths would warrant. Would
you like to make book on whether the parents of those three kids would
agree. I frankly don't care if I subject you to excessive drama as I
believe that is preferable to subjecting anyone to death by fire.

It's called Darwinism... Those who do stupid things, like buying
cheap/faulty appliances or taking wiring shortcuts, or overloading outlets,
etc. are taken out of the gene pool.

Sociecty is so busy protecting its "stupid" members that it will (if not
already) become so stupid that it will fail.

Let stupid people die by their own actions.

Try telling that to Jeff Wiznia!

SpamFree wrote:
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!

I would not think it that hard to ask UL about the research I have
attributed to them. My problem is that they pay their bills by getting
paid for their research efforts. Even if I bought a copy of their
report the copyright would still prevent me from posting it on line. Is
it your position that if I can't spoon feed you the supporting research
that I should not make reference to it?

I didn't see the calculations you referred to would you help me out and
point me to the postings that contain those calculations that I missed.
Did I miss someones posting that indicated a source for some research
that invalidates my willingness to depend on the testing done by UL?

Is it somehow illogical to assert that the length of the spiral armor
measured along the spiral coupled with the lower conductivity of steel
makes it a poor Equipment Grounding Conductor (EGC) unless the turns are
shorted to each other so that the larger cross sectional area of the
sheath can then make up for those factors? Why does corrugated armored
cable not have a bonding strip while the spiral tape armored cable does
have one? I've installed thousands of feet of the spiral armor type and
several hundred feet of the corrugated armor type. The post
installation testing of each type yields very similar results in terms
of the Equipment Grounding Conductor loop voltage drop.

UL's tests of armored cable that is armored with spiral wound
interlocking metal tape show that the armor alone is an inadequate EGC.
I may indeed have misunderstood why that is true but that does not
mean it is not true. Your position would appear to be that the spiral
tape must be an adequate EGC. On what are you basing that assertion?
What testing have you done or can you point the rest of us to that
supports your conclusion? If the spiral tape armor is adequate as an
EGC then why do the manufacturers install the bonding strip? The
addition of the bonding strip to the sheath is not without cost. Do you
believe that the manufacturers install it for some other purpose than
bonding the turns of spiral interlocking metal tape armor to each
other? If so what purpose do you allege the bonding strip serves.

What I do believe in this matter is that UL is acting in good faith. I
cannot see what UL would have to gain by declining listing to a simpler
cable construction that passes the listing standard. They are not the
only laboratory that conducts electrical product testing so if they
decline listing to a product that does meet the examination standard
they would simply loose that manufacturers listing fees to another
laboratory such as Southwest Research or ETL. I depend on the results
of laboratory testing. I am willing to depend on the laboratory listing
mark to determine whether an electrical component of a buildings wiring
system is suitable for it's intended use. You and a few others here
keep insisting that the reliance of myself and others here on the
laboratory listing make us somehow wrong. Fact is I've offered more
evidence than you have for our respective positions.
--
Tom H

According to SpamFree :
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.

Let's not start all this again, and look at something else - Canadian CEC
hasn't permitted cable sheath to be a ground for at least 30 years,
has _never_ approved armored cable with that "ridiculously small gauge
[bonding] wire", and has insisted for at least 30 years on a full size
copper ground conductor.

Cable armor is physical protection and little more.

The facts are simple: the cross-sectional area of cable armor is small,
perhaps not even as much as a copper wire. It's steel, not copper. Steel
rusts. Even when galvanized, the edges rust. Even if aluminum, the
manufacturing process will not produce long-term high conductance joints.

It's small cross-sectional area to begin with. Rust makes it smaller. It's
really long. It's brittle. An impact can destroy the electrical conductivity
if it cracks the strip. One must NOT rely on the conductivity of cable
sheath or box clamps for ground continuity.

There's a reason that current carrying conductors are copper, not steel.

IIRC, US "MC" cable is armored with a full size copper ground. Use _that_.

In Canada, that's all we're allowed to use.

Tom is right. Cable armor is a lousy ground. It's just that reactive impedance
is _not_ the reason why it's lousy.

[If I recall my calculations right, several hundred feed of cable armor will
have an equivalent impedance of a few microhenries. At 60hz, the reactive
impedance is insignificant - nowhere near enough to affect breaker trip.
It's like saying "skin effect" matters at 60hz. Skin effect exists. But
at 60hz it can be totally ignored.]
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

(Chris Lewis) wrote:

According to SpamFree :
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.

Let's not start all this again, and look at something else - Canadian CEC
hasn't permitted cable sheath to be a ground for at least 30 years,
has _never_ approved armored cable with that "ridiculously small gauge
[bonding] wire", and has insisted for at least 30 years on a full size
copper ground conductor.

I realize that you're Canadian and have a patriotic reason for
asserting the superiority of the Canadian Electrical Code however I
have an equally patriotic reason for asserting the opposite. In fact,
what Canada does wiring-wise has IMO as much relevance as the
electrical code of ... oh, say Bulgaria g. Canada doesn't allow AC?
Well that's nice to know. They probably do have special problems
wiring igloos g.

Cable armor is physical protection and little more.

The facts are simple: the cross-sectional area of cable armor is small,
perhaps not even as much as a copper wire. It's steel, not copper. Steel
rusts. Even when galvanized, the edges rust. Even if aluminum, the
manufacturing process will not produce long-term high conductance joints.

It's small cross-sectional area to begin with. Rust makes it smaller. It's
really long. It's brittle. An impact can destroy the electrical conductivity
if it cracks the strip. One must NOT rely on the conductivity of cable
sheath or box clamps for ground continuity.

So you say. However NYC, hardly a slouch in the imposition of onerous
regulations, has always insisted on the use of AC (nowadays with the
follower wire) and in using the armor as the EGC. Only in the last few
years have there been the minutest changes to allow NM in some very
suburban style non-rental houses. Commercial and rental buildings are
still conduit or EMT or AC. I believe many of the large older US
cities are in the same situation.

If the problem is as severe as you and Horne assert it would seem
logical that, needing the rodent-protecting capabilities of armored
cable, NYC would have changed to MC long ago. But they haven't.

Further, do you realize that there are hundreds of thousands (perhaps
millions) of feet of old style (non-follower-wire) AC installed in
thousands of buildings much of it dating to the forties and earlier?
And that old-style AC is being used as a ground by its very nature.
The metal box with the switch or the device is connected to the armor
of the AC by a screw (not a clamp), the armor of the AC is connected
to the load center metal (probably your denigrated steel) by another
screw, and the load center is connected to the ground (likely the
water main). Whether it actually forms an E(quipment) ground depends
on the connection between the device and the box but in the case of
direct wired lamps (isn't this Horne's dramatic case) it's almost
certainly electrically bonded.

So applying your horror scenario, if a fault develops in the lamp or
the box or in part of the cable the weak and ineffective armor will
not be able to carry enough current to blow the circuit breaker and
the home owner (or tenant), presuming a defective bulb, will be
electrocuted when he investigates. Alternatively the AC will heat to
incandescence (your earlier assertion and presumably Horne's dramatic
case) and burn the building down.

Wow! I guess the NYC electricians guild hasn't thought of this. Just
think of the work replacing all that old-style AC with
more-expensive-than-new-style-AC MC. Just think of the mega bucks
rolling in.

OK, I'm being sarcastic but the point stands. If old-style or
new-style AC represented any significant danger then there'd be moves
afoot to replace it (mandatorily) and there certainly wouldn't be any
more installed. Isn't this what's happening with Knob & Tube?

There's a reason that current carrying conductors are copper, not steel.

Aw come on! The current carrying conductors have to be wound around
screws and bent in tight arcs. I'd be the first to agree that steel is
not suitable for this use.

Tom is right. Cable armor is a lousy ground. It's just that reactive impedance
is _not_ the reason why it's lousy.

[If I recall my calculations right, several hundred feed of cable armor will
have an equivalent impedance of a few microhenries. At 60hz, the reactive
impedance is insignificant - nowhere near enough to affect breaker trip.
It's like saying "skin effect" matters at 60hz. Skin effect exists. But
at 60hz it can be totally ignored.]

I realize that you're Canadian and have a patriotic reason for
asserting the superiority of the Canadian Electrical Code however I
have an equally patriotic reason for asserting the opposite. In fact,
what Canada does wiring-wise has IMO as much relevance as the
electrical code of ... oh, say Bulgaria g. Canada doesn't allow AC?
Well that's nice to know. They probably do have special problems
wiring igloos g.

That's a stupid comment!
About equivalent to saying "Yeah they use lighted palm frond torches in
Florida or Hawaii"!
A reason for quoting the Canadian code was probably merely to point out
"Here is an authority not unknown for good safety practices in many
technical fields that regulates to the following standard."

The problem with using the BX cable armor as a ground is probably due
to the difficulty of making and maintaining a good electrical
connection to the armor at the ends of the cable. The clamps at the
boxes are not the most reliable.

And how do you deal with plastic boxes? The dedicated copper ground
wire is much easier to connnect to.

Mark

But is BX armor cable ever used with plastic boxes? I don't think
metal or even plastic conduit is used with plastic boxes, ... is it?
I would assume that metal conduit or cable would mandate the use of
metal boxes? --Phil

Mark wrote:

The problem with using the BX cable armor as a ground is probably due
to the difficulty of making and maintaining a good electrical
connection to the armor at the ends of the cable. The clamps at the
boxes are not the most reliable.

And how do you deal with plastic boxes? The dedicated copper ground
wire is much easier to connnect to.

Mark


--
Phil Munro Dept of Electrical & Computer Engin
Youngstown State University
Youngstown, Ohio 44555

"Terry" wrote:

I realize that you're Canadian and have a patriotic reason for
asserting the superiority of the Canadian Electrical Code however I
have an equally patriotic reason for asserting the opposite. In fact,
what Canada does wiring-wise has IMO as much relevance as the
electrical code of ... oh, say Bulgaria g. Canada doesn't allow AC?
Well that's nice to know. They probably do have special problems
wiring igloos g.

That's a stupid comment!
About equivalent to saying "Yeah they use lighted palm frond torches in
Florida or Hawaii"!
A reason for quoting the Canadian code was probably merely to point out
"Here is an authority not unknown for good safety practices in many
technical fields that regulates to the following standard."

I'm sorry, I took (and have taken over the years) it to mean, "Hey,
you dumb Americans. Wake up and learn what we Canadians, the smartest
people in the world when it comes to electrical codes, mandate for our
electrical installations. Just follow our lead and you'll be alright;
second-best maybe but OK."

I only know of one thing the Canadians have to teach us and that's how
to set up a single payer health care system but then again most
countries of the developed world, probably even Bulgaria, could teach
us something about health care systems.

Igloo construction too, perhaps g.

According to SpamFree :
"Terry" wrote:

I realize that you're Canadian and have a patriotic reason for
asserting the superiority of the Canadian Electrical Code however I
have an equally patriotic reason for asserting the opposite. In fact,
what Canada does wiring-wise has IMO as much relevance as the
electrical code of ... oh, say Bulgaria g. Canada doesn't allow AC?
Well that's nice to know. They probably do have special problems
wiring igloos g.

That's a stupid comment!
About equivalent to saying "Yeah they use lighted palm frond torches in
Florida or Hawaii"!
A reason for quoting the Canadian code was probably merely to point out
"Here is an authority not unknown for good safety practices in many
technical fields that regulates to the following standard."

I'm sorry, I took (and have taken over the years) it to mean, "Hey,
you dumb Americans. Wake up and learn what we Canadians, the smartest
people in the world when it comes to electrical codes, mandate for our
electrical installations. Just follow our lead and you'll be alright;
second-best maybe but OK."

That entire interpretation was silly when you consider I had also posted
a long discussion on how Canada is slowly adopting American style rules
for GFCIs in kitchens.

As Terry suggests, it was merely given as an example of an equally competent
electrical authority having reasons for and choosing not to go the
"use armor as ground" route.

I only know of one thing the Canadians have to teach us and that's how
to set up a single payer health care system but then again most
countries of the developed world, probably even Bulgaria, could teach
us something about health care systems.

Igloo construction too, perhaps g.

The US govt. and construction industry is rather fond of our R2000
construction methodology and quote/reference it a lot.

But they're not igloos.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

According to SpamFree :

Further, do you realize that there are hundreds of thousands (perhaps
millions) of feet of old style (non-follower-wire) AC installed in
thousands of buildings much of it dating to the forties and earlier?

Yup. Here too.

And that old-style AC is being used as a ground by its very nature.
The metal box with the switch or the device is connected to the armor
of the AC by a screw (not a clamp), the armor of the AC is connected
to the load center metal (probably your denigrated steel) by another
screw, and the load center is connected to the ground (likely the
water main). Whether it actually forms an E(quipment) ground depends
on the connection between the device and the box but in the case of
direct wired lamps (isn't this Horne's dramatic case) it's almost
certainly electrically bonded.

But of only minimal use as a ground. Those outlets were two prongs.

Just how good do you think 50 year old BX armor is as a ground, given
the oxidation it, the boxes, and clamps have gotten over the years?

And it's proposed to utilize this as a classic three prong outlet
grounding system. I've seen too much of that stuff to trust it.

Like the perfectly well panel-grounded chunk of BX in my friend's basement
that recently raised an enormous bang when a contractor slung a grounded
metal trouble light on it. You see, the end had a hot-armor short,
and the armor didn't have enough conductivity to trip the breaker.

Contractor: "we see this all the time...".

The house is about 100 years old.

So applying your horror scenario, if a fault develops in the lamp or
the box or in part of the cable the weak and ineffective armor will
not be able to carry enough current to blow the circuit breaker and
the home owner (or tenant), presuming a defective bulb, will be
electrocuted when he investigates. Alternatively the AC will heat to
incandescence (your earlier assertion and presumably Horne's dramatic
case) and burn the building down.

It happens. My co-author has seen it. And, IIRC, it was the cause
of the major casino fire in Vegas.

OK, I'm being sarcastic but the point stands. If old-style or
new-style AC represented any significant danger then there'd be moves
afoot to replace it (mandatorily) and there certainly wouldn't be any
more installed. Isn't this what's happening with Knob & Tube?

No. Very few jurisdictions, if _any_, are requiring mandatory
replacement of K&T, except in renovation work to new code. It's
the insurance companies in the private sector making K&T difficult
to insure. Despite the fact that aside from burial in insulation,
existing K&T is usually quite safe. Better than some later wiring
systems.

Similarly aluminum. Proven track record of hazard. Is there a mandatory
recall? No.

Asbestos.

UFFI.

Lead paint.

PT lumber.

Etc. Except for few cases (mostly commercial or local rules), none of these
are required to be removed. Mitigated in many cases, but rarely
mandatory removal.

You can argue that they're not as hazardous as some claim all you want, but,
they have been deemed hazardous, and _none_ of them are subject to mandatory
complete removal. Because it costs too much.

There's a reason that current carrying conductors are copper, not steel.

Aw come on! The current carrying conductors have to be wound around
screws and bent in tight arcs. I'd be the first to agree that steel is
not suitable for this use.

Bus bars and terminal tabs aren't steel either, they don't have to be bent
at all. Steel isn't suitable for that use either. Steel simply isn't
suitable as a conductor (except perhaps conduit, and even that we don't
permit).

[Canadian code, and I suspect US too, even doesn't really permit you to
use a metal box as part of a ground conduction path - you gotta bond
those copper ground wires together in NM, rather than run them
under different box screws. Except with US AC...]
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

According to :
Much to my
surprise, when I opened the roof, I saw that all the modern NM (romex)
had the outer coating removed across most of the attic.

Out of curiousity, "modern" in the sense of being more modern than
old BX, or "modern" in the sense of being recently manufactured NM?

I've seen this (right down to the bare wire in places) too.

It was wiring within the eaves of an old house. The roof structure
(esp soffits) was heavily damaged. We assumed Racoons at the time.
Could have been mice.

[No skeletons, the soffits were that badly "not there"]

It was NM all right, but not the stuff we've been using in the past
20-30 years with thermoplastic sheath. It was the stuff from
the 40's/50's with a varnished cloth/fiber exterior sheath.

Much more appetizing to varmints than PVC, especially if the varnish
had a salty taste.

After seeing that, I will never use NM cable in a
enclosed wall or ceiling. I will use it, for example, in my garage,
where its all exposed, but if I were to ever build myself a new home,
it would be all AC, greenfield, or steel conduit. Those wires were
uninsulated for 10 feet in some spots, with only bits and pieces of
the insulation remaining. If someone had gone in the attic, they
could have been electricuted. The mouse could have started on fire
and burned the whole place.

I think this answers which is better !!!

In sofar as being chewed on by mice. On the other hand, if you were using
ground-less BX and relying on the armor sheath for grounding, having those
mice pee on the cable (they pee on _everything_) means you have poor/no ground
in very short order and a wiring fault will result in a fire or potential
electrocution.

Nothing's perfect :-(

I like TECK cable most of all. Armored cable with thermoplastic exterior
sheath, and a real ground conductor. It's what's used in hostile environments
like mineshafts, and for outdoor events, like concerts or by mobile
carnival ride companies where large quantities of people and vehicles
will be running over it.

But TECK is real expensive.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

sounds like that was simply a case of the wrong fuse and wasn't the
fault of the spiral armor, the wires inside the armor were getting hot.

I think the worst electrical saftey issue I have seen (I live in the
US) is older 220V dryers. They are plugged in via a big 3 prong plug.
Two of the prongs are 220 and the third prong is a COMBINATION return
and saftey ground!!!. In my dreyer, the heating coils are across the
220 pongs. But the 110 volt motor and clock are connected from one 220
pin to the combination return / ground pin which also connects to the
chassis.

SO...if this retun line should fail OPEN someplace, there will be 110V
on the dreyer chassis (through the motor). And of course the dreyer
sits right next to the washer which is grounded by it's regular 110v
outlet. so by a simple open failure, there can be 110V ac across my
washer and dreyer. I see the cat walk across there all the time not to
mention the wife and kids. I was so concerned about this, that I
added a hard WIRE between the washer and dreyer chassis.

I think all newer dreyers have a 4 prong plug where the return and
saftey ground are seperate. But it boggles my mind that any saftey
organization would have ever alllowed the older three prong system.
Mark