bx cable for equipment ground

[pierre]

Re: bx cable for equipment ground

Roger
One of the best things I have read is your responese that you come here to read and learn, especially if the idea is different than yours. I like that attitude and share it with you, a great way to expand the horizons.

Joe
In answer to your question about the older style BX style Armoured Cable without the bonding strip, I would replace the existing wiring with new. But... some budgets cannot afford that, so we need to be realistic and use GFCI protection and hope for the best.

Like you, I check all of my new work, it saves the embarassment and sometimes a ton of troubleshooting later.

Pierre

 

[jmmyers]

Re: bx cable for equipment ground

Toni,

I have heard they have the same trouble with the suretest unit. It gives false bootleg ground readings about 10 feet from the panel.

Joe Myers

 

[jmmyers]

Re: bx cable for equipment ground

Pierre,

I do believe that replacement is the route to go. I don't like to compromise safety so GFCI protection is good but in my opinion not as good as replacement.

My largest concern is that the installation is safe. Is GFCI protection safe enough? While I don't think so, many do.

As an inspector I can not show indifference to one party because they can afford new and the other can not. If I do it for one, I should do it for all, regardless of financial status.

I want what it best for them, nothing more, nothing less.

I am sure that many electricians here want the same but as you state many can not afford the mercedes, they can barely afford the chevette.

It has been a great insight to the many posts here that brought new ideas and different methods of fixing the same problem. It is refreshing that I am always learning, I hope I never grow too old for that!

Joe Myers

 

[pierre]

Re: bx cable for equipment ground

When the budget gets in the way of doing the ultimate job, than our decisions get a lot harder. Safety is on everyones mind and the results of our work, even good intentions can be devastating. Its not easy, that is why the best are not installers, but electricians.

Pierre

 

[tonyi]

Re: bx cable for equipment ground

Originally posted by jmmyers:
My largest concern is that the installation is safe. Is GFCI protection safe enough? While I don't think so, many do.

The GFCI covers a multitude of possible future failure scenarios as I've outlined previously - but this is from strictly a cabling system POV.

Once the power goes beyond a box into some plugged in device in a receptical, the device or its cord can fail in any number of ways resulting in arcing that the GFCI won't be able to detect unless there's a gnd fault. If the place were converted to all 3-prong recepticals and people used genuine 3-prong devices, the chances of gnd fault (the 3-pronger will still have some measure of contact with the box via the backstrap/screws) detection are better. Sadly, there's a lot of two prong cord stuff on the market (like floor/desk lamps, cell phone chargers, radios, etc) where a bogus frayed cord has no path to fault if a high energy parallel arc develops. If it isn't enough to dead short and trip magnetically or on overload (for those older non-magnetic breakers) it can become dangerous. Lots of "outside christmas lights" fires each year due to bogus two wire cords. There was a multiple fatality one in the Albany NY area last winter I know of.

All of this applies to any modern or older cabling system, but the building materiels and methods in many older places can turn a small fire into a big one REAL quick...for example balloon framing. Its great for dropping cable down to a basement from a 2nd floor but it whips fires through walls like they were rocket propelled too. In a matter of minutes a whole building can become fully engulfed. This is one of the reasons why I don't just settle for GFCI when keeping old BX - I'll put in an AFCI followed by a GFCI receptical next to the panel (or use a Cutler combo AF/GF breaker).

I also tend to downgrade these branches to 15A even if they appear to be #12 wire all the way (usually they're #14, but I've seen the occasional #12 and 20A fuse or breaker). If loaded up, the #12 on the 15A breaker will trip before that older insulation gets too warm. IMO, keeping that cloth/rubber as cool as possible is important to keeping it alive and functioning safely.

 

[photon]

Re: bx cable for equipment ground

The "old style" type AC cable without the bond strip is commonly found in our working area in Atlanta, GA.-Some homes circa <1900 - The GA State Electrical Code - addendum to NEC - requires all AC type cable without the bond strip is limited to lengths of 6feet or less, or WILL BE protected by ground fault circuit interupters, whenever that circuit is modified in any way. I am told by city inspectors that without the bond strip, the ground return path is such a high impedance, the spiral of armor has literally gotten red hot -like a stove element- and caused many fires in historic homes.

 

[tonyi]

Re: bx cable for equipment ground

Sounds like GA has their head on straight about how to treat this older stuff . GFCI would be the bare minimum level of protection IMO to make the stuff effectively as safe as newer cabling systems.

 

[jmmyers]

Re: bx cable for equipment ground

Photon,

Thank you for the information. On occasion, I had the opportunity to witness that casing glowing and I have to say that I am truly amazed that more homes with the older style BX cable do not burn to the ground more often.

One thing that has always concerned me when using the BX style cable it the lack of continuity between the connections. It is pretty common for us around here to find them either disconnected completely from rust or corrosion, or just loose and fallen out of the connectors.

GFCI protection would be a good route to follow but it is not without limitations. One limitation would be that they are assuming continuity between those connections. While it could be tested easily enough to make sure it is connected, if one comes loose then everything beyond that is no longer protected, just as with the original installation. Now you are right back to square one, with the case glowing in the dark, correct?

Again, I appreciate your reply. If you have a chance to throw a few more suggestions my way, or a few other scenarios which you think may be beneficial, I certainly would appreciate those also.

My question would be that, of course GA has found the need for the additional protection with the BX cable, do you think it has done any good? Are homes really safer in GA where this is required?

BTW...I took a tour through Savannah last summer and got a chance to look at some of those historic homes. I really love the southern homes but I am not sure what it is about them that appeals to me! I would love to move south but I am not sure I could deal with that summertime heat and humidity! Maybe I could just get a winter job!

Joe Myers

 

[karl riley]

Re: bx cable for equipment ground

Joe, when GFCI protected, the BX would not glow, since only 5 mA of current would trip the GFCI.

Karl

 

[gwz2]

Re: bx cable for equipment ground

If that OLD BX is not continuous between the power source and the point of either;
1) An energized conductor shorted or contacting to the BX.

2) The BX is in series or parallel with the Grounded conductor,

the BX will not be carrying current to GLOW .

That does not prevent a person from being shocked, or worse, if the person happens to contact the section of BX which is in contact with the energized conductor, or sharing current with the grounded conductor.

 

[eprice]

Re: bx cable for equipment ground

Originally posted by jmmyers:
GFCI protection would be a good route to follow but it is not without limitations. One limitation would be that they are assuming continuity between those connections. While it could be tested easily enough to make sure it is connected, if one comes loose then everything beyond that is no longer protected, just as with the original installation. Now you are right back to square one, with the case glowing in the dark, correct?

Joe, are you thinking that an equipment ground is necessary for gfci to work? It isn't, since they work by monitoring any imbalance between the grounded and ungrounded conductors. If a circuit is protected by a gfci as discussed in this thread and the BX loses its continuity, a fault somwhere could go undetected until someone happens to contact the energized section of BX. But when that happens the result should not be, in theory, fatal since the gfci would limit current through that person to 5 mA. So, even in this case having the gfci protection would be better IMO than the original, un-protected situation.

 

[tonyi]

Re: bx cable for equipment ground

Originally posted by jmmyers:
Now you are right back to square one, with the case glowing in the dark, correct?

No. If the armor is broken somewhere, then the high resistance current path back to the panel that could turn it into a glowing filamant doesn't exist anymore. With busted armor, it essentially becomes a pure ungrounded 2-wire system.

The GFCI will still be protecting some section(s) of cable before the break as is intended. Downstream from the break, its entirely possible that a fault to the armor or a box could result in the armor/boxes becoming "hot". They could stay in this hot contition until such time that someone or something touches them and causes enough leakage to trip the GFCI.

There's one fairly obscure failure mode I can think of when the armor is broken at some point that could cause the armor to light up - It would require a longish run of cable with a hot/armor fault on one end and a neutral/armor fault on the other. In essence, a localized (because of the previous upstream armor break) hot/neutral short through the armor.

This one is a real long shot though, it requires 4 conditions to happen before it becomes dangerous - previously compromised armor integrity, a hot fault, a neutral fault, and a length of cable long enough to have enough resistance to keep the breaker from tripping on overload.

There's also a fair chance this kind of obscure failure could be detected by an AFCI depending on how the faults needed to produce it developed over time.

[ November 07, 2003, 10:55 AM: Message edited by: tonyi ]