ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Top Posters(30 Days)
sparky 8
Recent Posts
2017 NEC Changes
by gfretwell. 12/18/17 11:03 AM
Nec circuit protection
by Jkhayward. 12/18/17 09:56 AM
Dimmable LED 2x4 lay in fixtures
by HotLine1. 12/17/17 10:04 PM
Holiday Wishes to all!!
by sparky. 12/17/17 03:45 PM
Casino Wiring methods
by HotLine1. 12/09/17 10:44 AM
New in the Gallery:
Gallery Test
Popular Topics(Views)
243,103 Are you busy
179,552 Re: Forum
170,452 Need opinion
Who's Online Now
0 registered members (), 15 guests, and 8 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate This Thread
#62165 - 02/09/06 09:38 PM Old BX and AC  
BigB  Offline
Member
Joined: Mar 2004
Posts: 721
Tucson, AZ USA
I often deal with homes that were wired or rewired with the old style armored cable without the bonding strip. Most of them have had 3 wire receptacles added at one time using self grounding receps or pigtails to the box. Of course I know this cable is not approved for grounding, but now when I am called in for a new buyer I have to be the bearer of bad news and tell them the receps should go back to 2 wire.

There are probably millions of homes wired this way and whats more, the boxes are already grounded by the BX and there's nothing that can be done about that. And it seems that the most likely place for a H-G fault is going to be in that box, with all its old dried out insulation and perhaps a sharp edge on the BX to boot!

So am I doing the right thing here by telling homeowners they can't have grounding receptacles on this type of wiring? After all, it only extends the grounding six more feet from what's already there.

Or is the main risk that an uncleared ground fault will transfer to the user through the grounding pin?


Work Gear for Electricians and the Trades

#62166 - 02/10/06 05:19 PM Re: Old BX and AC  
BigJohn  Offline
Member
Joined: Mar 2004
Posts: 391
Boston, MA
As I understand it the risk is two-fold:
1) During a fault the grounded receptacle has the potential to energize grounded metal parts of an appliance, and there is nothing to clear that fault.
2) With BX the fault current will try to flow over the metal armor. Because the BX does not have a bonding wire, the armor will heat up much like a light-bulb filament. This is a potential fire hazard.

I'm not really sure if grounding each receptacle to the box is illegal. It doesn't appear to violate 406.3, especially if the receptacle yoke is in solid contact with the box.

However, at the panel, I would GFCI protect all the BX circuits with grounded receptacles, to comply with 406.3(D)(3)(c)

-John


#62167 - 02/11/06 01:08 PM Re: Old BX and AC  
Larry Fine  Offline
Member
Joined: Feb 2005
Posts: 693
Richmond, VA
Let's not forget that not interconnecting the receptacles' grounds is also required. You may have to use isolated-ground receptacles to accomplish this.

It's ironic that we can't depend on the metal sheath for grounding, but we have to defeat that same conductive property to be completely code-compliant.


Larry Fine
Fine Electric Co.
fineelectricco.com

#62168 - 02/11/06 03:28 PM Re: Old BX and AC  
winnie  Offline
Member
Joined: Sep 2003
Posts: 649
boston, ma
Huh?

The metal sheath of old BX cable, even if it is not suitable as an EGC, is certainly metal which 'may become energized' and therefore must be bonded to the grounding system.

-Jon


#62169 - 02/11/06 06:06 PM Re: Old BX and AC  
renosteinke  Offline
Cat Servant
Member
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
I thought that the NEC allowed the flex to be considered as the grounding electrode for lengths up to 6 ft? Am I wrong?

Over that length, well, is it not also possible to pull another wire? Or make the first receptacle a GFI type?


#62170 - 02/11/06 08:26 PM Re: Old BX and AC  
BigB  Offline
Member
Joined: Mar 2004
Posts: 721
Tucson, AZ USA
Jon, I think what Larry means is to isolate the grounding at the receptacle so as not to extend an ungrounded circuit which, technically, it is an ungrounded circuit since the BX is not recognized as a grounding path. Just like replacing a 2 wire recep with a 3 wire GFCI protected, no equipment ground but legal because of the GFCI. The IG recep will prevent the unrecognized grounding from extending to the user equipment.

reno....this is old old BX, not flexible metal conduit. And the lengths are considerably longer than 6 feet anyway.

[This message has been edited by BigB (edited 02-11-2006).]


#62171 - 02/11/06 08:54 PM Re: Old BX and AC  
Larry Fine  Offline
Member
Joined: Feb 2005
Posts: 693
Richmond, VA
Here's what I mean, specifically what is highlighted in bold:

Quote
From 2002 NEC:

406.3 General Installation Requirements. Receptacle outlets shall be located in branch circuits in accordance with Part III of Article 210. General installation equirements shall be in accordance with 406.3(A) through (F).

(D) Replacements. Replacement of receptacles shall comply with 406.3(D)(1), (2), and (3) as applicable.

(3) Nongrounding-Type Receptacles. Where grounding means does not exist in the receptacle enclosure, the installation shall comply with (a), (b), or (c).

(b) A nongrounding-type receptacle(s) shall be permitted to be replaced with a ground-fault circuit-interrupter type of receptacle(s). These receptacles shall be marked “No Equipment Ground.” An equipment grounding conductor shall not be connected from the ground-fault circuit-interrupter type receptacle to any outlet supplied from the ground-fault circuit-interrupter receptacle.

(c) A nongrounding-type receptacle(s) shall be permitted to be replaced with a grounding-type receptacle(s) where supplied through a ground-fault circuit interrupter. Grounding-type receptacles supplied through the ground fault circuit interrupter shall be marked “GFCI Protected” and “No Equipment Ground.” An equipment grounding conductor shall not be connected between the grounding type receptacles.


[This message has been edited by Larry Fine (edited 02-11-2006).]


Larry Fine
Fine Electric Co.
fineelectricco.com

#62172 - 02/11/06 11:29 PM Re: Old BX and AC  
winnie  Offline
Member
Joined: Sep 2003
Posts: 649
boston, ma
Got it. It gets a little contradictory, since the reason that we are considering using the GFCI is that the old BX is _not_ considered suitable to be an equipment ground, but we don't want to connect it because it might be an equipment ground [Linked Image]

I guess the problem is that the code section being considered discusses installation _without_ equipment grounds, but doesn't really address situations where you have _insufficient_ equipment grounds.

-Jon



Member Spotlight
mxslick
mxslick
Atomic City, ID USA
Posts: 803
Joined: October 2004
Show All Member Profiles 
Featured:

2017 Master Electrician Exam Preparation Combos
2017 NEC Electrician
Exam Prep Combos:
Master / Journeyman

 

Shout Box
Powered by UBB.threads™ PHP Forum Software 7.6.0
Page Time: 0.013s Queries: 14 (0.002s) Memory: 0.7954 MB (Peak: 0.9524 MB) Zlib enabled. Server Time: 2017-12-18 20:33:34 UTC