Can I use the old flexible conduit?

On Sunday, December 24, 2017 at 10:39:49 AM UTC-5, snipped-for-privacy@aol.com wrote:

Burford's experience is limited to the Russian internet troll farm where he lives in the basement. Do they even have inspectors there?
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On Sat, 23 Dec 2017 23:14:03 GMT, Iggy

There are several versions of "bx" cable. The original was just the spiral jacket - and is no longer considered a ground. The next version had a "ribbon" or "tape" conductor running the length inside.. The third version got a bare copper wire ground.
I believe the current versions are called MC and AC. AC is "armored cable" - steel? armor and aluminum ribbon bonding strip that allows the armor to be used as a ground (250.118(9)).
MC is "Metal Clad" and has no bonding ribbon, and a full circuit ground conductor. (article 330) It is an aluminum sheath IIRC.
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replying to Clare Snyder, Iggy wrote: Yep, I'm just talking about this guy's old and wonderful stuff good for another 50-years...if that's what it is and not actually empty BX that literally is flexible conduit.
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BX was outlawed in Chicago I believe because people would cut the wires at the same time as the shield so now you use greenfield and add the wires after the shield is cut.
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In alt.home.repair, on Sat, 23 Dec 2017 23:14:03 GMT, Iggy

Is there any relevance to "matched" impedance when dealing with house current? If it matched, what would it match?
Are you thinking about electronics, not electricity? Like matching output transformer impedance to speaker impedance.
In fact, what is the point of using the word impedance? Aren't we talking about plain old resistance, with no capacitative or inductive component?

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replying to micky, Iggy wrote: No, there's really no relevance to "matched", I was just giving some credit to the NEC of how a copper or aluminum wire might be a slight improvement over steel. Thus, Impedance is all of those other words and why it's so vital to electronics and speakers. Although, that's also why a slight improvement really doesn't matter when we're talking big dirty power and not transformed filtered small power. Therefore, why electronics and speakers don't care 1-bit if there's no ground nor how "approved" a ground is.
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On Sunday, December 24, 2017 at 10:44:11 AM UTC-5, Iggy wrote:

You just keep digging the hole deeper. Look at any modern electronics and the incoming power circuitry is always protected by MOVs that are connected from the hot and neutral to ground for surge protection. Same thing on phone line inputs and similar. With no ground, there is nowhere to shunt a surge to before it gets to the electronics. And the quality of the ground matters too, per the above discussion on impedance.
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On Sunday, December 24, 2017 at 11:26:59 AM UTC-5, trader_4 wrote:

I should have qualified that to say modern electronics that's supplied with a grounded plug. To those electronic appliances, it does matter whether or not you have a ground.
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On Sun, 24 Dec 2017 08:26:52 -0800 (PST), trader_4

Most of the things you are talking about only have 2 wire line cords so the ground is not important at all for any internal protection. The MOV connects line to neutral, usually with a 250v or so MOV. When you have a connection (antenna, satellite, cable or phone) you should have primary inlet protection. This is best done at the interface where it comes into the house, connected to the service ground but having supplemental protection at the equipment may do some good too. That might be compromised by the BX, depending on exactly how much impedance the armor creates. I doubt it is worth ripping out walls to fix it tho. If this is really a concern, you can always fish Romex to those few receptacles. Most of the stuff in your house will not be affected at all.
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On Sunday, December 24, 2017 at 12:31:53 PM UTC-5, snipped-for-privacy@aol.com wrote:

I agree and that's why I made my follow on post. But electronics that do have a grounded plug, eg computers, laser printer, dishwasher, refrigerator, washer, dryer, will typically have MOVs that shunt to ground and the electronics in those will benefit from the protection.
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On Saturday, December 23, 2017 at 11:53:40 PM UTC-5, micky wrote:

No

You're right, there is nothing to match. You just want the impedance of the ground path to be as low as practically possible.

There is always some capacitance and inductance involved. You can model a cable by a number of inductors in series and capacitors between them that go across the conductors. At 60hz, it's not much of a factor. But the ground path on occasion has to serve as the path for transients, eg a lightning surge. And to that the impedance of the path matters greatly. Even for a sudden direct short, the impedance matters, because again, it's not a 60hz event, there are high frequency components. With more impedance you'll see a higher voltage on the whole end of the ground path where the fault occure ed.
I suspect those kind of considerations went into the newer BX type cables because the ones that still rely on the outer metal jacket for the ground have included a thin wire inside. I suspect part or maybe all of it's purpose is to provide a straight, short path for the current. Because otherwise you already have a long coiled path for the current in the spiral jacket. It's one continuous piece of metal from end to end, right? It's just that it's spiraled onto itself. If the spiral edges make perfect contact with each other, then it would be like a pipe, a direct path. If they were perfectly insulated where they contact each other on every turn, it would look like a very long inductor. I suspect in practice, it's some of both. Putting that additional bare wire inside makes it less of an inductor, as well as shortening the effective length, which lowers both the resistance and impedance. I suspect that's why they did it.
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wrote:

This is more of a theoretical problem than a demonstrated one but the thought is that the extra impedance caused by the spiral wraps in the cable armor might prevent the over current device from operating in a fault condition. I suppose if the cable was long enough it could be a problem tho. The "fix" in AC cable was just a thin strip of the armor material that is actually scrap resulting from the manufacturing process run along with the conductors that effectively shorts out the "choke" created by the armor. The reality is, in 2000, when I tested an old BX job built during WWII, the cable armor still presented less than an ohm if impedance at every receptacle in the building. (Using an Ecos ground impedance tester) To create this "choke" you would need each revolution of the armor to be insulated from the one next to it. Where this is more likely to cause a problem is with point of use surge protectors that require the ground to be effective. The very short duration transients will have trouble being shunted out, even with a fairly low impedance in the armor.
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On Sun, 24 Dec 2017 10:33:39 -0500, snipped-for-privacy@aol.com wrote:

Causes problems with GFCI devices as well, perhaps?? or AFCI?
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wrote:

I can't think of a reason why it would. Any choke effect of the armor would be common mode affecting the other two conductors and cancel itself out at the GFCI. In fact the coupling into EMT would be a greater effect. The reality is I have one GFCI circuit here feeding lights and receptacles around the back yard that is a few hundred feet long, most in EMT with some RNC and the GFCI is fine with it in spite of all the hysteria I have heard about the coupling problem.
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On Sun, 24 Dec 2017 11:31:29 -0500, snipped-for-privacy@aol.com wrote:

I was thinking more GFCI outlets - not breakers - not feed-through --- but still just a question.
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On 12/24/2017 9:33 AM, snipped-for-privacy@aol.com wrote:

I always heard it was the resistance of the much longer length of much smaller cross-section, maybe low conductivity steel, if the spiral did not bond to the adjacent spirals. But impedance includes more.

Those protectors do not work primarily by earthing a surge. They work primarily by clamping the voltage on ALL the wires going to protected equipment to the 'ground' at the protector.
If you have H-N-G Romex, and there is 6kV at the panel, you have H supplying the protector and H-G sinking the surge. The voltage of the 'ground' at the protector will be about 2kV with respect to the 'ground' at the panel. But the voltage from ALL the wires to the protected equipment is limited to a safe value.
Because a 'surge' is a very short duration event, there are relatively high frequency current components. That means the inductance of wires (H, N & G) is more important than the resistance. The current, and thus energy, that can reach a point of use protector is surprisingly small.
The likely much larger current from the panel to the earthing electrode(s) is similarly limited, and the panel 'ground'-to-earth voltage may be very high.
(You probably agree with most or all of this.)

Protection is not primarily by shunting to earth.
If you have only H and N as effective conductors, there is H supplying the protector and N sinking the surge. If there is 6kV at the panel the voltage of the 'ground' at the protector will be about 3kV with respect to the 'ground' at the panel. But the voltage between the wires to the protected equipment is still limited to a safe value.
============================================If an electrician suggests pulling Romex into flex (other than limited special circumstances) their opinions are not worth listening to.
BX has always been a tradename for an example of type AC wiring.
IMHO a circuit wired in old BX can be extended. (Your opinion?)
(The extension would often have to be AFCI protected. One method (which may not be the best) is to wire it through an AFCI receptacle where the new part of the circuit originates.)
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We basically agree on the surge protection

If you follow the NEC rules the AFCI has to be at the first receptacle in the circuit if you are not using an AFCI breaker. If you do not have an effective ground path and you want to use 3 wire receptacles you need GFCI protection.
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On 12/25/2017 1:08 PM, snipped-for-privacy@aol.com wrote:

What I remembered was the source of the addition could be an AFCI receptacle. You are right. If I remember right the AFCI first receptacle would then have to be readily accessible. The code panel seems intent on retroactively requiring AFCI protection.
If the first receptacle is AFCI (above, or to protect replaced receptacles) the wiring from the panel to the first receptacle is also protected from "series" arcs (may not be apparent to others).

The question is whether 'old' BX is an "effective ground path" so you can install grounded receptacles. IMHO it is a 'grandfather' condition.
If 'old' BX is not considered an "effective ground path", and you succumb to the increasing NEC insistence by installing an AFCI 'first' receptacle, does that provide adequate protection to install downstream grounded receptacles? AFCIs have at least 50mA (usually 30mA) ground fault protection. Doesn't make downstream receptacles GFCI protected, but should trip on ground current that would be carried by 'old' BX.
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From the 2014 NEC 210.12 (B) Branch Circuit Extensions or Modifications Dwelling Units. In any of the areas specified in 210.12(A), where branch-circuit wiring is modified, replaced, or extended, the branch circuit shall be protected by one of the following: (1) A listed combination-type AFCI located at the origin of the branch circuit (2) A listed outlet branch-circuit type AFCI located at the first receptacle outlet of the existing branch circuit

It needs to be 5ma GFCI. I am not sure they make a GFCI/AFCI receptacle device but a couple of manufacturers do make the breaker type. For the purposes of tripping an AFCI, I would trust the BX as a ground path if it tested OK with a 3 light tester. If it tested OK with a Suretest or Ecos (<1 ohm) I would have no problems with 3 prong receptacles anyway.
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On 12/25/2017 7:26 PM, snipped-for-privacy@aol.com wrote:

As I wrote, "you are right".

So 'old' BX is not considered an "effective ground path"? Wasn't it when installed - to carry ground faults to the metal wiring system and trip the breaker/blow fuse.

No problem when inspecting?
I have trouble imagining properly installed BX that, with a ground fault, would not trip an AFCI on 30 mA ground fault (not arc fault). An original circuit (before AFCIs) the circuit breaker/fuse would not trip on a 30mA ground fault. I don't see why GFCIs are required (if not in an area where GFCIs are required).
=====================================A common reason for rejecting code proposals is that no substantiating data has been submitted.
Up through when AFCI protection was required almost everywhere I don't remember any substantiating data supporting requiring AFCIs.
And that year there was a proposal to not require fire alarms be on AFCI circuits (nifty idea - when there may be a fire kill the fire alarms). It was rejected because there was 'no substantiating data that it would increase safety'. I kinda think there was never any substantiating data that fire alarms were fire hazards that needed AFCI protection. (I think fire alarm standards require alarms on GFCI/AFCI have battery backup.) =====================================When will the NEC require all receptacles be GFCI/AFCI/child-proof/weather-resistant?
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