bx cable for equipment ground

[Guest]

Re: bx cable for equipment ground

Originally posted by iwire:
<snip> Something else to think about, if we did not ground anything, we would be safer still. But now I am into Bennie's domain.

When I was a kid I got my first buzz. My neighbor had their dryer outdoors. We were playing ball and everytime I bumped the dryer I got a tingle. It was explained to me that the dryer chassis was hot and that I was somewhat grounded through my shoes to the concrete slab. I wore canvas sneakers with rubber soles. I wore cotton socks. There was no moisture on the slab.

Would I have been safer if I was more grounded?

How would I make myself more grounded?

Would I have been safer if I was less grounded?

How would I make myself less grounded?

Would the dryer fault have been cleared if the dryer were properly grounded (no N-G bond)?

Would I have been safer if the dryer was GFCI protected?

Would a ground have been important if the dryer was GFCI protected?

../Wayne C.

 

[iwire]

Re: bx cable for equipment ground

A GFCI will not prevent you from getting a shock under any circumstance, it will limit the duration, you are still going to feel 5MA at 120 volts before the GFCI trips, they are fast but they are not psychic.

Now maybe Bennie can jump in here but if you where not to bond your service to ground you would not receive shocks through you and into the earth.

But OCPDs would not trip either if a conductor makes contact with whatever, setting you up for a shock when you are not expecting it.

I believe you would now need ground fault monitoring.

Like I said this is more up Bennie's alley, although you could look up in the code book for isolated systems (health care)

 

[Guest]

Re: bx cable for equipment ground

It seems like in a more perfect system we would use both hot legs in every circuit. We would not need a neutral. We would not have a ground. All plug-in devices would be double insulated-- or maybe all devices within reach. All circuits would be GFCI & AFCI. You still might get a buzz, but you'll walk away unassisted (as opposed to being carried away by six close friends in a box).

../Wayne C.

[ September 27, 2003, 05:38 PM: Message edited by: awwt ]

 

[tonyi]

Re: bx cable for equipment ground

To clarify the GFCI on 2-wire (or old BX) for those without a code book on hand... You CAN have downstreams, they just can't have gnd wire interconnect on them. A breaker or fed through receptical would be perfectly fine.

As a practical matter, many places with old BX, 2-wire NM, or K&T are also full of plaster and lath, have fancy mouldings, elaborate plaster crowns, (now) unmatchable fancy lincrusta/anaglypta wall coverings, elaborate wainscoating etc. If those branches are otherwise sound, a GFCI or AFCI can eliminate having to do a lot of very expensive architectural restorations to repair our wreckage that can quickly add up to far more than rewiring the whole place from top to bottom.

Myself, I'd feel (electrically) safer in an old place with old BX and AFCI's on everything than in a new place with NM and plastic boxes and only AFCI's in the BR's. I've yet to see a rodent that could chew through that old steel armor...but I did find a dead squirl in the attic of an uncle's apt building attic that had chewed through some Romex and caused a branch in some apartment's to go dead at one point.

 

[pierre]

Re: bx cable for equipment ground

In reply to Joe Myers question about old wiring, there are extensive studies being performed to figure out how to deal with the impending situation of 'Aging' wiring in the country. I am curious to see how the AFCI installation to old wiring and circuits is performing.

Are there any situations that are causing the AFCI breaker to trip?

Pierre

 

[jxofaltrds]

Re: bx cable for equipment ground

Pierre

AFCI kept tripping because of a flying splice. Something i would not have found without it.

The handheld GFCI tester showed everything OK. The minute a load was applied the AFCI tripped.

I have heard that where neutrals of different circuits are connected to each other will also cause it to trip.

Mike P.

 

[don_resqcapt19]

Re: bx cable for equipment ground

Mike,

AFCI kept tripping because of a flying splice. Something i would not have found without it.

What exactly was wrong with the "flying splice" to cause the AFCI to trip the circuit?
Don

 

[dana1028]

Re: bx cable for equipment ground

Originally posted by tom baker:
Dana: A GFCI can be used to replace a non grounded receptacle. A GFCI does provide a ground, however a GFCI does not require an "ground" or equipemtn grounding conductor to operate.
However, installing a GFCI where no equipment ground is present is a trade off in safety, the code makeing panel recognizes this, but it is felt to be safer on a GFCI than on a circuit without an equipment ground.

Tom - you made a statement above that makes me scratch my ear and wonder if I've missed something important...."A GFCI Does provide a ground..." - that is something completely new to me.

I'm well aware [at least I thought I was] of what a GFCI does provide and am familiar with the replacement provisions.

But IF a GFCI does provide a ground - then why is it not permitted for those installations under 250.114 (now I'm quoting Don Rescapt from a previous forum discussion).(I talking about 2-wire installations with no ground provided).

[ September 24, 2003, 11:32 AM: Message edited by: dana1028 ]

 

[roc]

Re: bx cable for equipment ground

GFCI outlets are great, but I understand they have a tendency to trip for no good reason. So for things like a refrigerator an old 2-prong outlet would be replaced with a standard 3-prong grounded outlet.

If the existing wiring is vintage AC cable ("BX" trademark) acting as the grounding conductor that is not corroded or otherwise deteriorated, and the wiring is not readily accessable, then what do ya do?

2002 NEC 406.3(D)(1) would require a grounding type replacement outlet connected per 406.3(C), which just requires the outlet to be connected to the grounding conductor. There is a FPN which references 250.118 for acceptable grounding means as an advisory.

Is it done that way intentionally to grandfather older grounding methods that may not meet the letter of the current code ... like the vintage AC cable ("BX") without a bonding strip/wire that would not meet the 250.118 requirements?

If an electrician is upgrading a old 2-prong outlet to a grounded 3-prong outlet on these systems would he test to verify the wiring provides a low impedance fault-current path, in addition to verifying the casing is not corroded?

 

[jmmyers]

Re: bx cable for equipment ground

How many of you are testing the BX style cable casing impendece when you are using it for a ground?

Thanks Bob (iwire), I appreciate your answer, it looks as though you are the only one that understood the question.

To all of those that are tallking about GFCI protecting the circuit, is that how you are fixing the BX cable issue, meaning are you simply GFCI protecting the circuit?

If so, do you think that GFCI protecting the circuit is adequate protection, rather than replacing the wiring for those circuits? When the cable casing is connnected to the service equipment which would provide a ground path (thanks to the metal casing and metal connectors) do you think it is safe with GFCI protection? NOT SAFER, SAFE! Are you measuring the impendence?

Finally, do you think those circuits should be left "as is"? Do you believe they are unsafe and should be upgraded?

Thanks,
Joe Myers

 

[big john]

Re: bx cable for equipment ground

Originally posted by roc:
GFCI outlets are great, but I understand they have a tendency to trip for no good reason.

That's something I was looking into recently because I was charged with replacing a receptacle that was being used (but not covered) by a freezer unit in a damp basement.

Apparently, phantom-trips were problematic with earlier GFCI's but as it stands now, it's safe to say that if a GFCI trips, there was a fault to ground somewhere. I've also posted a question on this board about it, and the concensus seems to be that every time anyone has dealt with "phantom tripping" on a new GFCI it was later found that there was in fact a real ground-fault.

-John

[ September 27, 2003, 04:15 PM: Message edited by: big john ]

 

[roger]

Re: bx cable for equipment ground

Joe, if the house is a wooden structure raised off the ground, no EGC is better.

If the house is slab on grade, a low impedance EGC to source grounded conductor would be desired.

Roger

 

[tonyi]

Re: bx cable for equipment ground

Joe, with old "BX" (i.e. no internal bond wire), the GFCI makes it safer for the user than what it was previously: 2-wire and ungrounded.

It also makes it safer from a structure POV - a line-armor, or neutral-armor short to that old armor or inside a metal box because of damaged insulations or punctured cable will cause a GFCI trip rather than cause the armor to become a glowing fillament. Even being unsuitable for EG, it should be able to pass the 5ma needed for a GFI trip as long as the connectors are even somewhat tight.

IMO, GFCI protected "old" BX, in absolute terms, is going to be safer than no-GFCI (or AFCI) and modern Romex. Its more physical damage resistant due to the armor. The metal boxes are better at containing burning junk than plastic too. It does lack an EG which some electronics can want. I see this as a usability issue rather than a safety issue though.

If I saw no continuity at all from a box to neutral, then it would need further investigation (this would be true of any modern AC system too) - I've seen a number of cobbed up Romex add-ons to BX/AC systems where someone didn't understand how the armored cable worked and just chopped off the Romex gnd on box entry.

 

[jmmyers]

Re: bx cable for equipment ground

Toni,

Thanks for answering. In reference to the GFCI protection being better that the old two wire approach....in the case where you are connecting this circuit to the service equipment with no breaks using metal connecters you are in fact creating a ground, correct? I believe I had read recently that the new style AC cable has that extra bonding strap present to ensure low ground impendence. Would you install the GFCI protection AND test the impendence of the casing? Since no one here, electrician or otherwise, has stated to me that they are testing the impendence, I am assuming this is not the SAFE route to go with. I don't think they would be testing it in my area since you are not testing it in your area, correct?

In this case you would use GFCI protection on that circuit and forget about the grounding issue with the cable casing, even though newer requirements state the cable should have the bonding strap. Is that a correct statement of how you would handle this situation?

What I am looking for here is the best possible scenerio on how to handle the BX cable, I am not looking to bust anyone's bubble, just looking for the safest possible alternatives such as replacement, GFCI protection or whatever else it would take to make this the safest possible installation.

If the scenerio you are offering is indeed GFCI protection of the circuit, would you please PROVE to me that this installation is safe.

To everyone that has replied to this thread....I am interested in beating this issue to death until I come up with the safest possible solution when dealing with BX style cable. Don't be afraid to lend your opinion here, there is no right or wrong. Just please be able to back up what you say is safe with facts, not personal opinions!

Joe Myers

 

[jmmyers]

Re: bx cable for equipment ground

Roger,

Thank you for the reply. I am assuming that you are saying that since the house is well above the ground clearance you would not be concerned about the grounding since people are not likely to get shocked by grounding themselves to the earth.

In the case with the slab, they are in close proximity to the ground so the chances of them grounding to earth and being shocked are pretty great.

I am assuming that is what you are stating but here is the question. Is there a scenerio where it would be possible for those persons to be grounded (I mean provide a ground path), such as an electrical wire in contact with a pipe somewhere that would provide the ground path, maybe enough for them to get severly shocked? Maybe they are touching a water pipe?

Depending on your answer, would you still maintain that is the safest possible installation?

Thanks, I really appreciate the input. I like to learn from everyone, especially those that think differently than myself. Maybe that is why we are all here, to learn from each other!

Joe Myers

 

[roger]

Re: bx cable for equipment ground

Joe to answer your questions concerning new AC or HCFC go here and spend some quality time.

There is no need to do any testing on the cable armor.

Roger

 

[roger]

Re: bx cable for equipment ground

Joe,

I like to learn from everyone, especially those that think differently than myself. Maybe that is why we are all here, to learn from each other

I definately agree with that stament. (you're a man after my own heart)

Roger

 

[tonyi]

Re: bx cable for equipment ground

Joe, I always test for armor continuity - even on new AC. It its NOT there, then there's an issue somewhere in the system that needs to be rectified.

This is just part of my own personal testing ritual. I've got one of the new Ideal AF/GF units and use its line status functions extensively. Its pretty good at finding branches with loose splices too. The L/N/G ohm readings will seem abnormally high. It indicates open grounds and a whole bunch of other issues. For the old non-bond wire BX and two-prong plugs I'll use a 3-prong adapter and gator clip to box. Its a wonderful diagnostic tool for determining the health of a branch.

On the old non-bond wire stuff, if there's no continuity to the panel, then the GFCI only buys you "people protection" against shocks. While people protection is all well and nice, its not buying you the line-armor neutral-armor short "wiring system protection" that a system with continuity would. Armor could still be energized by a failed hot wire insulation somewhere and go undetected by the GFCI (until someone grabbed it and created a leakage path).

IMO, if you have the old non-bond BX, and a GFCI breaker, and the branch has tested out as having continuity, then yes indeed it is "SAFE". Deteriorated insulations where something contacts a box or even internal to the cable on hot or neutral will leak enough to trip the GFCI (it has been my experience that the insulation degradations are mostly within boxes and an inch or so back inside the cable. Take a fresh 8" bite on some of the old stuff when there's enough slack and it'll strip off looking pretty darn good in most cases). When there's NOT enough current flowing on the armor to trip a 5ma GFCI, then there's certainly not enough current flowing through the armor back to the panel to cause it to become scorching hot and start whatever its fastened to on fire. In essence, the old stuff is electrically not much different than a no ground wire hot/neutral pull through long sections of Greenfield.

 

[jmmyers]

Re: bx cable for equipment ground

Tony,

Excellent post, you hit the nail right on the head.

The new ideal tester you are speaking of, is it something like the suretest model? What model are you using?

Is there any other scenerio that you can think of where people would not be protected against shock, if it were tested as you stated?

Thanks again.

Joe Myers

 

[tonyi]

Re: bx cable for equipment ground

Originally posted by jmmyers:
The new ideal tester you are speaking of, is it something like the suretest model? What model are you using?

Is there any other scenerio that you can think of where people would not be protected against shock, if it were tested as you stated?

If someone grabs a hot and neutral and there's no leakage path, they'll get fired up even when a GFCI is there. This is an issue on any cabling system though...

I've got the Ideal SureTest #61-155. Came in some combo kit with a breaker finder. The breaker finder was pretty worthless - its sender unit leaks to gnd and trips GFCI's. But I didn't care about that anyway since I've also got a Greenlee circuit seeker for that kind of stuff and it does a lot more than any common breaker finder does.

The only notable oddness I've found with the Ideal is it flags a bootleg ground if a receptical is within a couple of feet of the panel the branch originates from (ex. a lot of basement recepticals will be right next to the panel). It has to detect bootlegs by measuring impedence differences and a receptical so close to the panel with the wire being so short at that point its all pretty close to zero so it just can't tell the difference. Not a big deal, just something everyone needs to be aware of incase some inspector using one wants to gig you Once you're 3-4' from the panel there's enough measurable impedence that you can trust the bootleg red flags.