# AC/BX cable as ground



## 220wire (Aug 18, 2008)

We're doing a lighting replacement project and am wondering if we have add a egc to the AC cable coming through the ceilings. It is stranded THHN inside a steel armored casing no bonding strip and is a heavy durable steel. Can someone confirm that BX has the old rubber and cloth insulation on the cable and AC has the tiny bonding strip ran through it?


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## HARRY304E (Sep 15, 2010)

220wire said:


> We're doing a lighting replacement project and am wondering if we have add a egc to the AC cable coming through the ceilings. It is stranded THHN inside a steel armored casing no bonding strip and is a heavy durable steel. Can someone confirm that BX has the old rubber and cloth insulation on the cable and AC has the tiny bonding strip ran through it?


That is just flex, not BX, so you need to run a ground wire.


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## Big John (May 23, 2010)

I agree with Harry, with stranded THHN but no bonding strip, the description sounds like flexible metal conduit. If these are short lengths, you might be alright. See 250.118(6)


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## 220wire (Aug 18, 2008)

its 3/8, does that still constitute it as flex?


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## chicken steve (Mar 22, 2011)

The EGC of armored cable is dependent on it's listing

If in fact it does not qualify, read 410.44 exceptions no#1 , no#2 & no#3

3 _'outs' _right there


~CS~


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## Big John (May 23, 2010)

220wire said:


> its 3/8, does that still constitute it as flex?


 They make 3/8 flex, but that'd just be weird.

You 100% certain there's no grounding means? Like, have you broken some of the armor to see if there's actually a bonding jumper that's been cut back?


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## 220wire (Aug 18, 2008)

Big John said:


> They make 3/8 flex, but that'd just be weird.
> 
> You 100% certain there's no grounding means? Like, have you broken some of the armor to see if there's actually a bonding jumper that's been cut back?


 
100% theres no bonding anything inside, the reason for such concern. I think if its kept under 6' we might be ok


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## Southeast Power (Jan 18, 2009)

220wire said:


> 100% theres no bonding anything inside, the reason for such concern. I think if its kept under 6' we might be ok


Ok then,
You are gonna need to post a pic...


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## Pete m. (Nov 19, 2011)

220wire said:


> 100% theres no bonding anything inside, the reason for such concern. I think if its kept under 6' we might be ok


No. You won't. The cable you are describing is not permitted as an EGC. At least, not for today's standards.

At 6' or less, attached to a properly grounded system, it might be ok... I won't bet my lunch on it though.


Pete


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## Deep Cover (Dec 8, 2012)

Pete,

I've wondered why premade fixture whips (3/8" FMC) come with a ground in them. Nothing in the 2011 NEC makes me think that an EGC is required if kept under 20A and less than 6'. Am I missing something?


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## Dennis Alwon (May 9, 2009)

art. 250.118 (5)



> (5) Listed flexible metal conduit meeting all the following
> conditions:
> a. The conduit is terminated in listed fittings.
> b. The circuit conductors contained in the conduit are
> ...


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## Deep Cover (Dec 8, 2012)

So, maybe the manufacturers are covering their butts for (C)? Otherwise, I don't see anything that would require an EGC.


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## Pete m. (Nov 19, 2011)

Deep Cover said:


> So, maybe the manufacturers are covering their butts for (C)? Otherwise, I don't see anything that would require an EGC.


What the OP is describing may be "code worthy" in lengths under 6' but from my personal experience (seeing fires caused by BX cable) I wouldn't trust it. 

I do not believe it is a reliable return path for fault current due to the seemingly high impedance.

Pete


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## Dennis Alwon (May 9, 2009)

Pete m. said:


> What the OP is describing may be "code worthy" in lengths under 6' but from my personal experience (seeing fires caused by BX cable) I wouldn't trust it.
> 
> I do not believe it is a reliable return path for fault current due to the seemingly high impedance.
> 
> Pete


Agreed but if it is a whip there should be no issue as the impedance on 6' is not very great. I have seen the old BX without the metal strip in it actually glow from a short that wouldn't trip the breaker


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## 220wire (Aug 18, 2008)

Pete m. said:


> What the OP is describing may be "code worthy" in lengths under 6' but from my personal experience (seeing fires caused by BX cable) I wouldn't trust it.
> 
> I do not believe it is a reliable return path for fault current due to the seemingly high impedance.
> 
> Pete


How many fires have you seen? I thought BX was safer than MC. Luckily there's class P ballast in them


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## Deep Cover (Dec 8, 2012)

Pete m. said:


> What the OP is describing may be "code worthy" in lengths under 6' but from my personal experience (seeing fires caused by BX cable) I wouldn't trust it.
> 
> I do not believe it is a reliable return path for fault current due to the seemingly high impedance.
> 
> Pete


I'll be a little more specific about my question (slight side step from the OP)...

If I were to make my own fixture whips with 3/8" FMC, with listed connectors, protect the conductors at 20A, and keep the length under 6', would I have to install an EGC in the whip?


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## Pete m. (Nov 19, 2011)

220wire said:


> How many fires have you seen? I thought BX was safer than MC. Luckily there's class P ballast in them


3. I'm no forensic engineer but it isn't a stretch when you see the outline of the BX coils on a truss with the signature char marks.

Pete


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## Pete m. (Nov 19, 2011)

Dennis Alwon said:


> Agreed but if it is a whip there should be no issue as the impedance on 6' is not very great. I have seen the old BX without the metal strip in it actually glow from a short that wouldn't trip the breaker


I do actually agree with you. 

Just saying... I wouldn't trust it... would I fail it on an inspection? 

No. I have no code verbiage to do so.

Pete


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## Pete m. (Nov 19, 2011)

Deep Cover said:


> I'll be a little more specific about my question (slight side step from the OP)...
> 
> If I were to make my own fixture whips with 3/8" FMC, with listed connectors, protect the conductors at 20A, and keep the length under 6', would I have to install an EGC in the whip?


Sorry to say this... But, maybe. If the AHJ makes a determination that the FMC is installed to "provide flexibility for equipment that requires movement after installation" then yes an EGC would be required.

For a typical 2X4 lay in fixture I wouldn't see what I quoted as requiring an additional EGC.

Pete


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## Deep Cover (Dec 8, 2012)

Pete m. said:


> Sorry to say this... But, maybe. If the AHJ makes a determination that the FMC is installed to "provide flexibility for equipment that requires movement after installation" then yes an EGC would be required.
> 
> For a typical 2X4 lay in fixture I wouldn't see what I quoted as requiring an additional EGC.
> 
> Pete


Thanks. We just changed to the 2011 and the wording in the 2008 could be interpreted differently.



> d. Where used to connect equipment where flexibility
> is necessary after installation, an equipment
> grounding conductor shall be installed.


Because of this wording, most EC's decided to run EGC's no matter what the circumstance.


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## Pete m. (Nov 19, 2011)

Deep Cover said:


> Because of this wording, most EC's decided to run EGC's no matter what the circumstance.


It is rare, thank goodness, that I see any fixture whips without an EGC. 

Pete


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## Dennis Alwon (May 9, 2009)

220wire said:


> How many fires have you seen? I thought BX was safer than MC. Luckily there's class P ballast in them


BX with the thin metal strip in it can be used as an equipment grounding conductor but the older BX without that metal strip cannot be used as an equipment grounding conductor.


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## HARRY304E (Sep 15, 2010)

Pete m. said:


> What the OP is describing may be "code worthy" in lengths under 6' but from my personal experience (seeing fires caused by BX cable) I wouldn't trust it.
> 
> I do not believe it is a reliable return path for fault current due to the seemingly high impedance.
> 
> Pete


I like the way it glows...:laughing:


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## Southeast Power (Jan 18, 2009)

Deep Cover said:


> I'll be a little more specific about my question (slight side step from the OP)...
> 
> If I were to make my own fixture whips with 3/8" FMC, with listed connectors, protect the conductors at 20A, and keep the length under 6', would I have to install an EGC in the whip?


Yes, 3/8" needs a ground.
You are using it for its flexibility, not because it looks nice.


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## Dennis Alwon (May 9, 2009)

jrannis said:


> Yes, 3/8" needs a ground.
> You are using it for its flexibility, not because it looks nice.


Not if the flex and the fittings are listed as an equipment grounding conductor. I bet most of it is listed that way- also it must meet the other conditions mentioned. Sure install an equipment grounding conductor -- I would


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## Deep Cover (Dec 8, 2012)

jrannis said:


> You are using it for its flexibility, not because it looks nice.


That is the exact interpretation that was cited previous to the 2011 code cycle. Now, with the new wording, I don't see that as a valid argument.


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## 220wire (Aug 18, 2008)

chicken steve said:


> The EGC of armored cable is dependent on it's listing
> 
> 
> 3 _'outs' _right there
> ...


Defendant on NEC listing or manufacturer? The NEC needs a section on how to make assumptions when things aren't black and white. Was there ever a listing for AC with cloth and rubber insulation?


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## Big John (May 23, 2010)

Am I missing something? I didn't see anything in 250.118 that permits a cable assembly not to have an equipment grounding means. 

I've never seen the type of BX he's got, but that's what it appears to be.


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## chicken steve (Mar 22, 2011)

Dennis Alwon said:


> Agreed but if it is a whip there should be no issue as the impedance on 6' is not very great. I have seen the old BX without the metal strip in it actually glow from a short that wouldn't trip the breaker



_2nd_ that

the outer shell of old BX is something like 5-6X's the interior conductors

time and corrosion add to the R factor

~CS~


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## chicken steve (Mar 22, 2011)

220wire said:


> > Defendant on NEC listing or manufacturer?
> 
> 
> An NRTL _listing _follows every manufacturer widget we use
> ...


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## swimmer (Mar 19, 2011)

Dennis Alwon said:


> I have seen the old BX without the metal strip in it actually glow from a short that wouldn't trip the breaker


Because of resistance in the armor?
Because of resistance between the armor and the connectors?
I assume this old BX has no ground wire and the armor serves as EGC.


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## Big John (May 23, 2010)

swimmer said:


> Because of resistance in the armor?


 My understanding is that the spiraled armor acts like an inductor coil and exhibits a very high impedance. The bonding jumper in modern AC shorts out the turns of the coil and reduces the impedance and allows it to pass enough current to function as an effective EGC.

Next time someone pulls out a 30' length of that stuff, they should grab the DC resistance off that compared to a 30' length of normal armored cable.


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## RIVETER (Sep 26, 2009)

Deep Cover said:


> So, maybe the manufacturers are covering their butts for (C)? Otherwise, I don't see anything that would require an EGC.


(C) is describing three different conduit systems which in reality have to be made with about 8 connections to complete the egc system. The margin of error at the connections is a lot and I am wondering why getting all of that within 6 feet would be legal anyway.


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## Southeast Power (Jan 18, 2009)

Deep Cover said:


> Thanks. We just changed to the 2011 and the wording in the 2008 could be interpreted differently.
> 
> 
> 
> Because of this wording, most EC's decided to run EGC's no matter what the circumstance.


I'm thinking that just the design of a 2x4 requires a flexible connection. They are made to be removable.


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## Deep Cover (Dec 8, 2012)

This is where I split hairs. These fixtures are required to be secured to the grid, so after installation, they are not removable. In order to remove them, you would need to "uninstall" them.


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## Deep Cover (Dec 8, 2012)

RIVETER said:


> (C) is describing three different conduit systems which in reality have to be made with about 8 connections to complete the egc system. The margin of error at the connections is a lot and I am wondering why getting all of that within 6 feet would be legal anyway.


(C) is talking about the entire raceway system. Say you had a 3' fixture whip but in order to feed this circuit, you had to fish FMC 5' down to the panel. That 5', combined with the 3' fixture whip would be over the max 6' of flex allowed and you would have to install an EGC in both sections of flex.


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