Fishing a ground conductor thru old BX/Greenfield?

Reply

  #1  
Old 10-24-10, 06:30 PM
scoob8000's Avatar
Member
Thread Starter
Join Date: Apr 2005
Location: USA
Posts: 183
Received 0 Votes on 0 Posts
Fishing a ground conductor thru old BX/Greenfield?

We're about to move into a new house (to us, it's actually a old house)....

The previous owner did a lot of rewiring. But there are a few rooms still with ungrounded outlets.

Most of the outlets in question are fed with older two conductor BX wire. Most go back to various junction boxes fed by new NM wire. Currently the shield is being used for the ground.

Rather then tear up the walls to replace the old BX, what are the chances of fishing a insulated ground from the outlet box to the junction? (Most are short runs). And if possible, is this acceptable?

Sorry for the long winded explanation, I couldn't figure out how else to explain it without photos.
 
Sponsored Links
  #2  
Old 10-24-10, 06:34 PM
Member
Join Date: Oct 2010
Location: USA
Posts: 126
Received 0 Votes on 0 Posts
Others will chide in soon, but you would need to know the size of the bx. Why is the sheathing no longer good enough for ground?
 
  #3  
Old 10-24-10, 06:43 PM
HotxxxxxxxOKC's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2006
Location: USA
Posts: 8,044
Received 0 Votes on 0 Posts
You cannot use the metal sheath as a the ground on BX. Are these circuits grounded at the main panel?

As for fishing a new insulated ground wire, it all depends, but depending on the age of the home you may have to punch some holes in the walls.
 
  #4  
Old 10-24-10, 06:46 PM
Member
Join Date: Oct 2005
Location: Milwaukee WI
Posts: 1,338
Received 0 Votes on 0 Posts
BX was cable manufactured with a steel spiral jacket. How old is the BX? If it's cloth and rubber insulated, it's hard to imagine you would have enough room, or be able to remove the old conductors, and even if you did, the BX assembly was not intended to have additional conductors added and I doubt it would be code-complaint. Sorry if that's a run-on.

However, if it is Greenfield (Flexible metal conduit with field-installed conductors), there is no problem as long as you stick to the capacity limits.
 
  #5  
Old 10-24-10, 07:13 PM
ray2047's Avatar
Member
Join Date: Mar 2006
Location: USA
Posts: 33,597
Received 13 Votes on 11 Posts
Is there paper between the individual wires? If there is paper packing around the wires it isn't Greenfield.
 
  #6  
Old 10-24-10, 07:53 PM
scoob8000's Avatar
Member
Thread Starter
Join Date: Apr 2005
Location: USA
Posts: 183
Received 0 Votes on 0 Posts
chopnhack,

Perhaps it is sufficient. I'm just a little paranoid I guess.


HotinOKC,

It looks like the junction is fed with NM which is grounded at the panel. The junction box is grounded, and the sheath is grounded (by the clamps) but I don't trust it. Especially for my computers, ups's, etc.


ArgMeMatey,

I have not measured, but it's a a good bit bigger in diameter than the armored wire you would buy today. Granted I have not dug in enough to see if there's other material (paper) in there. From what I can tell the conductors have a rubber insulation and no cloth that I can see.


Sorry I'm so vague, we have not actually moved in yet so I have not really dug in. Just trying to do a little research before I do.
 
  #7  
Old 10-25-10, 08:16 AM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 14,958
Received 33 Votes on 28 Posts
Given the unknowns of what is on the existing circuit that you want to ground I would add new grounded circuits and leave the old stuff alone.

BX is a cable assembly. You will not be able to fish new conductors into the sheath.
 
  #8  
Old 10-25-10, 12:47 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
Some BX provides a good ground and some does not -- depends on how old "old" is. It cannot be retrofitted with a ground wire in the sheath. If the ground is bad, the cable can be replaced or you can fish a #12 ground wire to each box through the wall space.
 
  #9  
Old 10-25-10, 05:47 PM
scoob8000's Avatar
Member
Thread Starter
Join Date: Apr 2005
Location: USA
Posts: 183
Received 0 Votes on 0 Posts
Thanks for the replies..

I guess there's really no way around it, I'm eventually going to replace it all.

I could run an extra ground wire, but since I'll need to access the outside the box in the wall already anyway, I might as well run some new. All said and done I was trying to avoid "damaging" the plaster walls.

We'll be in the house tomorrow and I'll see if I can do a little investigating.
 
  #10  
Old 10-25-10, 05:59 PM
ray2047's Avatar
Member
Join Date: Mar 2006
Location: USA
Posts: 33,597
Received 13 Votes on 11 Posts
All said and done I was trying to avoid "damaging" the plaster walls.
You may still be able to. The old boxes or often nailed to the studs and can be removed by cutting the nails between the stud and the box with a Sawzall or even a hacksaw blade. You can then either pull the box out of the wall or push it in. That leaves a large enough hole to fish the wire. You replace it with old work boxes. Since the old work boxes are usually a bit larger minor dings aren't a problem.
 
  #11  
Old 10-25-10, 08:00 PM
scoob8000's Avatar
Member
Thread Starter
Join Date: Apr 2005
Location: USA
Posts: 183
Received 0 Votes on 0 Posts
Originally Posted by ray2047 View Post
You may still be able to. The old boxes or often nailed to the studs and can be removed by cutting the nails between the stud and the box with a Sawzall or even a hacksaw blade. You can then either pull the box out of the wall or push it in. That leaves a large enough hole to fish the wire. You replace it with old work boxes. Since the old work boxes are usually a bit larger minor dings aren't a problem.
Good idea there! Something else to pay attention to tomorrow!
 
  #12  
Old 10-26-10, 09:33 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
Originally Posted by chopnhack View Post
Why is the sheathing no longer good enough for ground?
Old armored cable (brand name BX) relied only on the spiral steel for ground. As that steel rusts the ground quality deteriorates significantly. On a bad piece, you can short it out and the spiral will glow red but the breaker will not trip. New AC is made with an additional continuous bonding strip welded to the inside of the spiral which maintains continuity as the sheathing corrodes over time. The bonding strip must be terminated correctly at the box fittings to maintain good grounding.
 
  #13  
Old 10-26-10, 10:02 AM
Member
Join Date: Apr 2009
Location: Boston
Posts: 146
Received 0 Votes on 0 Posts
Originally Posted by HotinOKC View Post
You cannot use the metal sheath as a the ground on BX.
I would like to see some evidence backing this statement up. BX is slang for AC. AC cable has a bonding strip because the metal sheath is an acceptable grounding conductor.
 
  #14  
Old 10-26-10, 10:59 AM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 14,958
Received 33 Votes on 28 Posts
Originally Posted by Danny7633 View Post
I would like to see some evidence backing this statement up. BX is slang for AC. AC cable has a bonding strip because the metal sheath is an acceptable grounding conductor.
The original metal clad cable did not contain the bond strip and is not suitable for use as a ground.
 
  #15  
Old 10-27-10, 12:45 AM
Banned. Rule And/Or Policy Violation
Join Date: Jan 2010
Location: KS
Posts: 1,896
Received 0 Votes on 0 Posts
Originally Posted by Danny7633 View Post
I would like to see some evidence backing this statement up. BX is slang for AC. AC cable has a bonding strip because the metal sheath is an acceptable grounding conductor.
Since the OP has stated that it is rubber insulated wire, and given that it is behind plaster/lath, that indicates that it is in fact true BX and not 'slang' for AC. Using BX sheath as a ground has caused many a fire (I had one myself caused by glowing BX run in a dirt crawlspace under the house), which is why it is not allowed whether it has a bonding strip or not. AC has the bonding strip welded to the spiral along its entire length to ensure ground integrity, and it requires proper termination at the box. BX just had the strip kind of in there.
 
  #16  
Old 10-27-10, 04:44 AM
scoob8000's Avatar
Member
Thread Starter
Join Date: Apr 2005
Location: USA
Posts: 183
Received 0 Votes on 0 Posts
I'm somehow doubting this stuff has the bonding strip in it, but I didn't get a chance to look yet. Perhaps today.

I did a little recon however. If the boxes come out semi easily, it will not be too bad to run new NM and toss in some old work boxes. 3 boxes, and about 30' or wire.

Now the kitchen with counter height outlets will be another story..
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
 
Ask a Question
Question Title:
Description:
Your question will be posted in: