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MC w/ground loading from BX w/o ground

3K views 27 replies 6 participants last post by  Amazingglazier 
#1 ·
a terminal section of one of my circuits that is used entirely for lights loads off of an old BX cable that has no ground and aluminum wires coated in cloth insulation (old). i used MC cable with ground. in the JB, i just put a green ground screw and pigtail the loading ground wire to it.

when testing the circuit extension, i temporarily installed an outlet so i can test it using a little Sperry plug-in indicator with 3 lights. it indicated that there was an open ground...

my question is: is that normal considering that i did pigtail the "open ground" in the conversion JB around a ground wire? is the test tool designed to only detect whether the ground goes all the way to the ground bus bar in the panel? i am curious how the tool works in general, i.e. how it makes the detection.

thanks
 
#2 ·
1 You can not extend an old 2 wire circuit.
2 The bx is not grounded, and you connecting to the box still means it is not grounded.
3 A meter with the correct knowledge can tell you if the ground extends to the main panel.
4 The tool compares the voltage between hot and neutral, and hot and ground and lights the correct lights.
 
#3 ·
1 You can not extend an old 2 wire circuit.
it is not really an extension, more like a replacement.

i could swear i heard different advice before, i.e. that you can extend it.

but what really are you supposed to do when you have that scenario and you don't have access to replace the old cable all the way to the panel, i.e. when you are doing partial house remodeling like myself?
 
#4 ·
in the future, i do plan to have the rest of the house demoed so as to be able to reach the old cable and replace it. but doing it all at once is impractical to impossible, to say the least.

the important question is: does extending it present a considerable hazard? COMPARATIVELY SPEAKING ... i'm sure it's not as good as being grounded but it wouldn't have been grounded anyway if it were the old cable all the way, i.e. if i hadn't replaced the terminal section.

there is no doubt in my mind that this kind of stuff is being done in the world of partial remodeling, in fact, i am positive that it is one of the most common phenomena and there are established procedures. people do renovate just one room in a 100 yr old house without clearing all the way between it and the panel, there is no doubt about that.
 
#5 ·
there is no doubt in my mind that this kind of stuff is being done in the world of partial remodeling, in fact, i am positive that it is one of the most common phenomena and there are established procedures. people do renovate just one room in a 100 yr old house without clearing all the way between it and the panel, there is no doubt about that.
But it doesn't make it right,I am sure one of the sparkys will chime in.
You will NOT be able to use the three prong recepticales on this circut unless you fix the ground properly.
 
#12 ·
M3 Pete said:
I thought with BX and other 2-wire metallic conduit systems that the outer conduit was the ground. You have to have an electrical connection between the conduit and all metal boxes, all the way back to the panel.

No?

Or is his problem likely due to an open ground connection somewhere back toward the panel, like the conduit not making effective connection with a box?

I'm no electrician, just asking.
The BX would serve as ground only if the first box it ran from was in fact grounded to the panel. That does not appear to be the case here.
 
#18 ·
The missing connection could be anywhere. He might have a plastic box put in by a previous owner, or any number of broken/bad connections.

In my non-expert opinion, I'd say he is no worse off now than when his BX was ungrounded and feeding other lights. Not ideal, to be sure.

Is there a way to test for ground in jb's along the circuit? Like using a neon tester with one lead on the hot and the other on the box? If so, he could at least try to isolate the bad ground connection and maybe fix it.
 
#16 ·
The purpose of the ground is to protect the person if a wire should come loose in the appliance. Without ground YOU would become the closest thing to ground. With the GFCI and no ground wire if a wire should come loose and touch the appliance it will detect the change in voltage and trip the outlet.
 
#19 ·
amakarevic said:
well fine but what would you do to make things right? there are a lot of people on this forum who are like code or theoretical nazis with next to no connection to what is practical or possible or feasible.

if you had 10 ft to redo between two lights at the end of a 150 ft long 2-wire BX circuit at the end of a house, would you tear all the walls to "do it right" or would you find a workaround?

jeez :icon_confused:
Absolutely correct! It would be the work around for 90 % of the people doing it.
 
#22 ·
i said:

a terminal section of one of my circuits that is used entirely for lights loads off of an old BX cable that has no ground and aluminum wires coated in cloth insulation (old). i used MC cable with ground. in the JB, i just put a green ground screw and pigtail the loading ground wire to it.

when testing the circuit extension, i temporarily installed an outlet so i can test it using a little Sperry plug-in indicator with 3 lights.

 
#23 ·
amakarevic said:
i said:

a terminal section of one of my circuits that is used entirely for lights loads off of an old BX cable that has no ground and aluminum wires coated in cloth insulation (old). i used MC cable with ground. in the JB, i just put a green ground screw and pigtail the loading ground wire to it.

when testing the circuit extension, i temporarily installed an outlet so i can test it using a little Sperry plug-in indicator with 3 lights.3
Slow deep breaths amakarevic..........
 
#24 ·
What I am trying to say is this, you are using a new wire that does not have the ground hooked up you will NOT be able to use three prong outlets unless they are GFI outlets and even then you will have to label them as NOT having equipment ground.
If it were me I would put a note in each box stating what you did for future reference,because people forget and people move.As for the JB is it going to be accessable once you are done?
 
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