Need advice on old "BX" wiring

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Old 04-16-11, 04:25 PM
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Need advice on old "BX" wiring

My son is seriously considering buying an older home (built 1900) which we walked through yesterday. In the basement I found a standard breaker box (100 amp) but all the wiring that could be seen is BX and every outlet in the house is a 2 prong (no ground). I didn't remove any outlet covers so don't know if the boxes are metal or how the cable is connected. We are wondering what the best way is to deal with this type of wiring without having to rip into every wall replacing everything. Anything in particular we should look for?
 
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Old 04-16-11, 04:51 PM
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Since it was built around 1900 and has BX it has been rewired at some point, besides having the panel changed. IMO if he likes the house, this would be very low or non-existent on the deal breaker list of buying the house.

BX that has the bonding strip installed, combined with the steel armor, IS an approved ground path. The only thing that would need to be done is to swap the 2 prong receptacles with grounded ones, bonding them to the steel boxes. You will not find this strip on the inside of a box, the best place to look is at the panel. Many electricians working with BX cut and remove the outside jacket, than wrap or fold the bonding strip up the cable, install the bushing and insert the cable into the proper connector.

There is thousands of houses out there using BX and ungrounded outlets that have no problems. I wouldn't see it being an issue for your son.

BTW - How did your determine it is BX? I know many people that use the terms BX, Greenfield and MC interchangeably when they are quite different wiring methods.
 
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Old 04-16-11, 06:20 PM
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What I'm calling "BX" is the twisted metal sheathing over what appears to be two cloth or rubber covered cables. I didn't do a real good inspection of the breaker box. Don't know if the cable has a bonding strip or not. What if it doesn't? Does this make things more difficult as far as being able to get some grounded plugs hooked up?
 
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Old 04-16-11, 06:35 PM
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If the cable is about 1/2" in diameter then it is likely BX. If there is no bonding strip then the steel armor is not a legal ground and some other method go grounding will need to be used to have a ground. This can be a ground wire ran back to the panel, or install some new circuit using NM-b cable (romex) Adding grounded receptacles many cases do not require damaging the walls with some know how and time. We do it all the time.
 
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Old 04-16-11, 07:54 PM
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You could always install gfi's with no equipment ground stickers. The bx would actually provide enough of a path to trip the gfi without using an outside source. Very hard to explain my thinking.
 
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Old 04-16-11, 08:23 PM
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The bx would actually provide enough of a path to trip the gfi without using an outside source.
A ground is not required to trip a GFCI.

I'd probably test the grounding with a 100 watt light bulb. With no ground strap it isn't code but I 'd be reasonably confident it would work. Adding the GFCI would assure personal safety.
 
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Old 04-16-11, 09:04 PM
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I was thinking, if you have a plug strip sitting on a second floor hardwood floor in a wood-framed house like mine, and one of the internal backstabs comes out and touches the housing in an ungrounded circut with gfi protection, there is not going to be enough current flow, if any to trip the gfi, while that bx will provide a low-enough resistance connection to actually trip it, although maybe not enough to trip the 20A breaker.
 
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Old 04-17-11, 06:44 AM
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Originally Posted by Justin Smith View Post
I was thinking, if you have a plug strip sitting on a second floor hardwood floor in a wood-framed house like mine, and one of the internal backstabs comes out and touches the housing in an ungrounded circut with gfi protection, there is not going to be enough current flow, if any to trip the gfi, while that bx will provide a low-enough resistance connection to actually trip it, although maybe not enough to trip the 20A breaker.
In my opinion, there would be enough of a ground to trip the breaker too although it is not an approved by NEC ground. The fact is, in this situation, it's all you have unless you run a ground to each receptacle or completely rewire the house. I like Ray's recommendation.
 
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Old 04-17-11, 09:20 AM
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Originally Posted by CasualJoe View Post
In my opinion, there would be enough of a ground to trip the breaker too although it is not an approved by NEC ground. The fact is, in this situation, it's all you have unless you run a ground to each receptacle or completely rewire the house. I like Ray's recommendation.
I would also agree.

Look here ---> 25 characters!
 
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