Grounding of two wire circuits

[Dennis Alwon]

I am not sure the OP knows what he has. He says that he has BX with no ground, than says this:



His tracer could very well be the sheath bond wire and I believe this now makes the sheath a possible EGC.

That is what I was thinking. There is obvious inexperience here and we can help educate. :grin:

 

[tryinghard]

The use of grounded circuit conductor as equipment grounding also on a range or dryer is not a parallel path it is only one path connected to the load as well as the frame of the range or dryer. Now if another grounded object is to contact the range or dryer then it may carry some of the grounded circuit conductor current...

kwired I'm not pouncing ya just using your prompt above to point out to all what you reveal.

And this other grounded object will receive current (electrocution) according to the level of resistance to source; the problem is the other grounded object can be a person leaning on the dryer while touching the washer, or baby crawling on the tile floor touching the dryer to help mommy, or dog licking dryer, or person touching range while touching sink, or...

Fact remains its current where it does not belong and in cases like these it's only there because the manufacture doesn't use a transformer for the 120v loads - or not bond the neutral - the parallel path forms with the other grounded object often a person! These are exceptions only recognizing existing installations (with certain criteria met) these cases can occur but new applications appreciate the rule rather than the exception mainly due to shock hazard.

Thanks for the use of your wording and promt

 

[al hildenbrand]

. . . I will be replacing a ceiling fan for a customer that has only "two wire BX" circuits no ground. . . . I don't do too much residential.

I am not sure the OP knows what he has. He says that he has BX with no ground, than says this:

its the old style BX with no ground at all besides the tracer

His tracer could very well be the sheath bond wire and I believe this now makes the sheath a possible EGC.

I agree that the initial confusion and "heart of the question" lies with what is actually installed above the customer's ceiling fan. Start with the age of the dwelling. Consider the visible signs of the wiring at the dwelling (examine the exposed wiring were the framing is not covered, like at the service center, etc.) Is the ceiling fan location a new addition, or is it in the part of the dwelling unchanged since first constructed.

There is a wealth of information about the history that can be gathered in a matter of moments, just by looking. If, in looking, one sees things that are unfamiliar, more time is necessary. "Old style BX" is part of one wiring method, Armored Cable - Article 320 in the 2008 NEC. Armored Cable has a history back to the beginning of the 1900s and, when installed by the Code of the day, when part of an assembly that provided continuity to Grounding Electrode System, was considered a grounding means.

The Armored Cable sheath bond wire (perhaps the "tracer" the OP refers to?) was introduced in the 1950s and improved the performance of the armor as a grounding means. After the NEC of the '50s required the sheath bond wire, installing old style non-bond-wire AC in new installations meant that the sheath could not be a grounding means.

The pre-'50s installations generally get grandfathered in as grounding means, unless there is local ordinance to the contrary.

Bottom line, I suspect, as Dennis has stated, the ground is already there, just connect to the box, which is the EGC (equipment grounding conductor) in a typical AC wiring method.

Now:

Don't forget AFCI protection 210.12(b)

If the 2011 NEC is in effect, this is a good reminder. If, as I suspect, the OP customer is under the 2008, then AFCI is not part of the discussion as this is an existing ceiling fan that is being replaced.

I am curious if the lighting outlet above the ceiling fan is rated for fan support? Or whether the support of the fan is side stepping the box by being directly hung on the framing? If the old original ceiling box was already replaced with a fan support listed assembly, was it done with the correct materials that maintains the armored cable EGC continuity?

 

[Castrovinci]

The use of grounded circuit conductor as equipment grounding also on a range or dryer is not a parallel path it is only one path connected to the load as well as the frame of the range or dryer. Now if another grounded object is to contact the range or dryer then it may carry some of the grounded circuit conductor current.

BX (AC) cable is required for the sheath to have adequate fault carrying capabilities. (320.108)

MC cable sheath can, but does not have to be an equipment ground conductor. (330.108)

Old AC cable does not have bonding conductor installed like newer AC which helps assure a lower impedance during a fault, but is still grounding potential if connected to grounded enclosures with proper fittings.

Yes, I meant the path would be parallel just at the load (dryer or range) as they will be connected together right?

In reading section 320.100 BX (AC) cable (IMO) can only be used as a ground if it contains that internal bonding strip (tracer). So if it?s that older sytle and it?s possible that it doesn?t have that tracer it would be null. I will have to look further at the fan, I can't say for certain without pulling down that fixture that this particular branch has a tracer and "Listed connectors etc". I only took a glimpse at the two pronged recp and semi open boxes. At this point I am only estimating on it and wanted to see what worst case scenario is....running a new wire. This way I can provide both quotes.

320.108 to me says "to act as an equipment grounding conductor...Meaning if it is to act as. This is could be taken as if.

Originally Posted by Castrovinci
Thank you this is exactly what I was looking for. It sums up my whole question

In Summary it must have one of the following

1. GFCI Protection
2. Separate Ground ran in accordance to 250.130(C)
3. Be made of Insulated material and have no exposed parts
4. Be inaccessible to unqualified personnel

I don't think exception #4 applies to wiring methods with no ready means for grounding.

I do believe this would apply 410.42a says It shall be connected to an equipment grounding conductor OR be insulated from EGC and other surfaces OR be inaccessible to unqualified personnel....
subject to interp there.

 

[Castrovinci]

Sorry I was posting close to the same time as AL

I suspect this was a grandfather thing all along and I appriciate the history on the BX. So if this was pre tracer time then technically if I did just put the ground to the box and call it a day it would be ok despite the interperation of the newer code.

 

[al hildenbrand]

. . . So if this was pre tracer time then technically if I did just put the ground to the box and call it a day it would be ok despite the interperation of the newer code.

From this side of my monitor's screen, I can't tell a thing about the history of the customer's dwelling. Also, I have no way of knowing any of the local ordinance, if any, that applies.

Practically, reading today's 320.108 and assuming it to be retroactive to the 1800s is a source of a lot of confusion.

It's way to easy to overthink this.

Get a multimeter out and measure the Ohms from the ceiling box to the Grounding Electrode System.

 

[tryinghard]

...I will be replacing a ceiling fan for a customer that has only "two wire BX" circuits no ground. My question is do I take the ceiling fan ground and tie it in with the neutral or do I just leave it off.

Read 250.24(A)(5) & 250.142(B) these are the rules on bonding the neutral downstream past the service disconnect, they exist to disallow current where it does not belong.

To answer your question; do not bond these together. Terminate the equipment ground to the metallic box. Back in the day the covering on BX with correct fittings was the equipment ground now-a-day's we use AC or MC both are listed in 250.118 as types of equipment grounding.

 

[Castrovinci]

Read 250.24(A)(5) & 250.142(B) these are the rules on bonding the neutral downstream past the service disconnect, they exist to disallow current where it does not belong.

To answer your question; do not bond these together. Terminate the equipment ground to the metallic box. Back in the day the covering on BX with correct fittings was the equipment ground now-a-day's we use AC or MC both are listed in 250.118 as types of equipment grounding.

Excellent thank you everyone!

 

[mivey]

The op's customer has BX. I am betting it is grounded, at least somewhat.

If it is what we called BX, it had no ground to really speak of (except for short runs). While BX is just GE's brand of armored cable from way back, we called the armored cable without a bonding strip BX (well, if we were being picky), and the cable with the strip AC.

The BX might have somewhat of a ground but it is pitiful over any real length. The spiral armor just made it have a high inductive impedance. Plus, modifications with improper terminations made the whole path weak at best.

If this cable has the bonding strip and the path has good terminations (look for remodels, new devices in old locations, etc), I would probably use the cable for a ground. Outside of that, it is a shot in the dark.

 

[mivey]

His tracer could very well be the sheath bond wire and I believe this now makes the sheath a possible EGC.

I missed that, and I would agree.

PS: Sorry Dennis

 

[mivey]

I do believe this would apply 410.42a says It shall be connected to an equipment grounding conductor OR be insulated from EGC and other surfaces OR be inaccessible to unqualified personnel....
subject to interp there.

I disagree but it would not be the first time I've been wrong. 410.42 (A) has the statement about unqualified personnel, but is not included in 410.42 (B) which is the part about luminaires connecting to ungrounded wiring methods.

 

[mivey]

So if this was pre tracer time then technically if I did just put the ground to the box and call it a day it would be ok despite the interperation of the newer code.

Nope. See 410.42 (B).

Get a multimeter out and measure the Ohms from the ceiling box to the Grounding Electrode System.

I would still question if it could carry enough fault current. There are ways to test this but I hesitate to elaborate. On another note, I wonder what kind of test loads one might find useful to carry around?

 

[al hildenbrand]

Get a multimeter out and measure the Ohms from the ceiling box to the Grounding Electrode System.

I would still question if it could carry enough fault current. There are ways to test this but I hesitate to elaborate. On another note, I wonder what kind of test loads one might find useful to carry around?

Mivey, you certainly have the right to do your wiring based upon your opinion. But your opinion is not the NEC in this case.

The NEC has consistently allowed armored cable as a grounding means since the wiring method was introduced in the first decade of the 1900s. And, over more than a century, the construction of armored cable has been tweaked to reduce its impedance.

BX is armored cable is AC.

Any version of armored cable, meeting the construction requirements of the NEC in effect at the time of its installation, and, being installed to the requirements of the NEC in effect at the time of its installation, continues to be a grounding means, by the NEC.

And, remember the OP is about a ceiling fan in a dwelling, a setting that generally has runs forming net like meshes of armored cable and other grounding means, further reducing impedance by parallel path. While you can mistrust the low Ohm reading on your multimeter, it doesn't change the NEC history of BX being a grounding means.

 

[mivey]

Mivey, you certainly have the right to do your wiring based upon your opinion.

Thank you. And I will.

But your opinion is not the NEC in this case.

But just you wait till I get "my" town...:grin:

The NEC has consistently allowed armored cable as a grounding means since the wiring method was introduced in the first decade of the 1900s. And, over more than a century, the construction of armored cable has been tweaked to reduce its impedance.

Tweaked twice if I recall.

BX is armored cable is AC.

Yes. As I said, BX was what GE called their armored cable. The BX name just stuck.

Any version of armored cable, meeting the construction requirements of the NEC in effect at the time of its installation, and, being installed to the requirements of the NEC in effect at the time of its installation, continues to be a grounding means, by the NEC...While you can mistrust the low Ohm reading on your multimeter, it doesn't change the NEC history of BX being a grounding means.

I consider the use of the old BX without the bonding strip as a grounding means to be an unsafe practice. I may be able to "get by" because of some grandfathering loop-hole but I don't expect I will take that path.

 

[mivey]

And, remember the OP is about a ceiling fan in a dwelling, a setting that generally has runs forming net like meshes of armored cable and other grounding means, further reducing impedance by parallel path.

Mesh-smesh. I see the "net" in a dwelling, especially those with wood framing, to be more like veins spreading out that do not cross enough to form a "net". If you are going to go down that path, the thing to consider is how many parallel paths go back to the source. I would bet you not many and the path back to the source is what is important when trying to trip the breaker.

If we did have some kind of "net" way out on the feeder, but not a parallel impedance-reducing path back to the panel, we have just increased the number of things that will get energized when we have a ground fault. There may not be sufficiently low enough impedance to trip the breaker but there is enough available fault current to electrocute someone.

I don't tend to be a fear monger but that is just not the type of system we should keep loading up with ground-hungry equipment. I realize the situation is probably worse with a receptacle than a fixture but if you are in for a penny, you are in for a pound.

 

[al hildenbrand]

. . . ground-hungry equipment. . .

And yet, the National Electrical Code does not support your opinion.

 

[kwired]

The real issue is how much increase in impedance are we looking at on this old AC cable that is carrying fault current?

Remember that available fault current, and length of the cable are also going to factor into this.

Will the impedance be enough that a properly sized overcurrent device will not open? Or will it just take more time to open because of the reduced amount of fault current caused by the impedance? If it will still trip that is better than no trip at all.

I find it a little hard to believe that a cable with 12 AWG conductors protected by a 20 amp OCPD with a ground fault will not be able to carry more than 20 amps which will allow the OCPD to open at some time depending on how much current is actually flowing.

Over the years the design changes of the cable were enhancements to allow for less impedance and not an attempt to make something non conductive into something conductive.

 

[mivey]

And yet, the National Electrical Code does not support your opinion.

To each his own. Some go by code minimums, some don't.

 

[al hildenbrand]

To each his own. Some go by code minimums, some don't.

I like bidding against those who go beyond the Code.

 

[mivey]

The real issue is how much increase in impedance are we looking at on this old AC cable that is carrying fault current?

Remember that available fault current, and length of the cable are also going to factor into this.

Will the impedance be enough that a properly sized overcurrent device will not open? Or will it just take more time to open because of the reduced amount of fault current caused by the impedance? If it will still trip that is better than no trip at all.

I find it a little hard to believe that a cable with 12 AWG conductors protected by a 20 amp OCPD with a ground fault will not be able to carry more than 20 amps which will allow the OCPD to open at some time depending on how much current is actually flowing.

Over the years the design changes of the cable were enhancements to allow for less impedance and not an attempt to make something non conductive into something conductive.

Read case one here:
http://www.nfpa.org/assets/files//PDF/Proceedings/Sleights_paper.pdf

Not an conviction against of BX per se but certainly worth considering. Probably more damning is the fact that the NEC started requiring the bonding strip in 1959 (I think).

Now I'm curious. Could one of you guys that have the old NEC code books look at them and see if the old AC cable without the bonding strip was approved as a grounding path method or if the addition of the bonding strip make it an approved grounding path method? I really don't know what the rule was back then.