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-   -   MC w/ground loading from BX w/o ground (http://www.diychatroom.com/f18/mc-w-ground-loading-bx-w-o-ground-139132/)

amakarevic 04-03-2012 01:04 PM

MC w/ground loading from BX w/o ground
 
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

jbfan 04-03-2012 01:12 PM

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.

amakarevic 04-03-2012 01:17 PM

Quote:

Originally Posted by jbfan (Post 891026)
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?

amakarevic 04-03-2012 01:49 PM

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.

Ravenworks 04-03-2012 02:27 PM

Quote:

Originally Posted by amakarevic (Post 891053)
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.

amakarevic 04-03-2012 02:39 PM

Quote:

Originally Posted by Ravenworks (Post 891084)
You will NOT be able to use the three prong recepticales on this circut unless you fix the ground properly.

i have a multitude of lighting as well as a bathroom fan in this circuit extension and they all work beautifully. the previous setup was similar in terms of fixtures but each fixture's ground wire was pigtailed locally as there was no ground wire running in the cable. so, i really didn't do anything different. effectively, the ground wire within the new MC cable is simply sitting dormant until the circuit gets changed up to that junction point. but i don't think i messed anything up compared to how it was before.

amakarevic 04-03-2012 02:46 PM

Quote:

Originally Posted by Ravenworks (Post 891084)
But it doesn't make it right.

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:

M3 Pete 04-03-2012 02:46 PM

Quote:

Originally Posted by jbfan (Post 891026)
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.

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.

sublime2 04-03-2012 02:48 PM

Put a GFCI in the box and your good to go.
Any short that may occur from a loose wire on the appliance making contact with it will be stopped by the GFCI since you don't have a ground.

amakarevic 04-03-2012 02:49 PM

Quote:

Originally Posted by M3 Pete (Post 891092)
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.

i also heard what you say in the 1st sentence but i think what you say in the 2nd is what the test utility expects in order to test OK.

amakarevic 04-03-2012 02:50 PM

Quote:

Originally Posted by sublime2 (Post 891094)
Put a GFCI in the box and your good to go.

Which box? The JB that joins the old with the new cable?

sublime2 04-03-2012 02:53 PM

Quote:

Originally Posted by M3 Pete
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.

sublime2 04-03-2012 02:54 PM

Quote:

Originally Posted by amakarevic
Which box? The JB that joins the old with the new cable?

No the outlet box your going to plug the appliance into.

amakarevic 04-03-2012 02:55 PM

Quote:

Originally Posted by sublime2 (Post 891101)
No the outlet box your going to plug the appliance into.

there will be none, all are lights on the extending branch

amakarevic 04-03-2012 02:57 PM

the most important question, again, is not whether the new setup is the way it should be in the perfect lala-land but more whether it introduces any defect compared to how it was before (2-wire BX all the way)


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