Pls help; 3-wire fixture off of 2-wire Bx receptacle

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Old 12-04-11, 12:05 PM
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Pls help; 3-wire fixture off of 2-wire Bx receptacle

Please tell me how I can connect a new 3-wire exterior light fixture (black, white, bare ground) off an old existing 2 black rubber coated wired receptacle?
the two black wires look rubber-coated, entering metal box through flexible metal sheath clamped to box. I think this is called Bx wiring...the receptacle is newer looking Leviton 15 Amp 125 Volt, Duplex Receptacle, Residential Grade, Non-Grounded, Ivory/Brown/White, 223 which has polarized slot; but no brass screw, only four silver screw terminals, two on each side. Each black wire is connected to a lower silver terminal screw on each side, leaving the upper silver screws open. I don't know which is line vs. load; i have multitester but don't know how to use it. Do I connect the new NM 14-2 romex black wire to one empty screw, and the white wire to the other empty screw on receptacle, and clamp the bare ground wire to the box? thanks; incredible google searching on this for two days and nothing close to an answer...
pdoyle
 
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Old 12-04-11, 12:12 PM
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Please tell me how I can connect a new 3-wire exterior light fixture (black, white, bare ground) off an old existing 2 black rubber coated wired receptacle?
You can't. Extending an ungrounded circuit is not code compliant. You need to run a new circuit.
 
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Old 12-04-11, 01:33 PM
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If your BX does not have a bonding strip in it, Ray is correct. However, if the bonding strip is present, then the cable sheath is the grounding path. This can be difficult to determine without exposed cable or without removing the cable from the connector.
 
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Old 12-04-11, 01:58 PM
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What does the bonding strip look like? I take it you would know it if you see it? Furthermore, what does it do differently to make the casing usable as a ground path?
 
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Old 12-04-11, 02:01 PM
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Sorry I didn't see it was BX. Following not necessarily Pro approved but I would test the ground by wiring a lamp holder to the metal box and the black wire. Use about a 60 watt light bulb in the lamp holder. If the bulb comes on at full brightness you can be reasonably certain you have a functioning ground. If so you can ground the new cable to the box. However to be fully code compliant as Tolyn said only use it as ground if the BX has a grounding bond strip included.
 
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Old 12-04-11, 02:11 PM
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Originally Posted by drooplug View Post
What does the bonding strip look like? I take it you would know it if you see it? Furthermore, what does it do differently to make the casing usable as a ground path?
The bonding strip is a small (16 - 18ga) uninsulated aluminum wire that is on the inside in direct contact of the armor sheath. Sometimes it is also flat. It guarantees a reliable grounding path, in conjunction with the metal armor sheath.
 
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Old 12-04-11, 02:23 PM
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Sigh. I don't think I have that in my old wiring.
 
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Old 12-04-11, 05:00 PM
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think i have bonding strip

I must have a bonding strip; but please confirm.
A thin ~18 ga. bare wire runs along the outside of the flexible metal sheath;
does that sound like it?
the receptacle it feeds has polarized slots.

but how can I tell which silver screw connector on receptacle I should attach the new fixture black, and white wires?
one of the two black rubber-coated wires running thrugh the Bx sheath is connected to the left lower screw connector, and the other black wire is connected to the right lower screw connector; and all four connector screws are silver. This leaves an open screw on the upper right, and another open screw on the upper left.
so;
  • pls confirm i have a bonding strip
  • pls instruct me where I will connect the new fixture black, and the white, wires to...i assume i ground the bare grounding wire with the clamp to the metal box.
Thanks! I haven't tried the light test, but i will tomorrow.
pdoyle
 
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Old 12-05-11, 05:46 AM
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Please answer last questions...

HI, please to clarify;
- after running light test, to which screws/box do i connect 3 fixture wires? of the two silver only screws on each side of receptacle, the lower left has 1 black wire, the lower right has the other black wire; leaving two upper screws open. I connect the ground wire to the box's clamp of sheathing?
-also, can i use a multimeter test instead of a light? don't have any open-wire light fixtures; do have a light 'tester' to show live circuit, and a multimeter.
thanks!
pdoyle
 
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Old 12-05-11, 07:46 AM
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I must have a bonding strip; but please confirm.
A thin ~18 ga. bare wire runs along the outside of the flexible metal sheath;
does that sound like it?
Yes, that is the bonding strip.

but how can I tell which silver screw connector on receptacle I should attach the new fixture black, and white wires
White wires to the silver screws. Black wires to the brass screws.

one of the two black rubber-coated wires running thrugh the Bx sheath is connected to the left lower screw connector,
Receptacles have no left or right. There is no top or bottom. Only screw color counts.

haven't tried the light test, but i will tomorrow.
No test needed because you have the bonding strip. Grounds are connected together and pigtailed to the box using a grounding screw in a tapped hole.

can i use a multimeter test instead of a light?
No. The 120v bulb acts as a load test. A ground that works on a multimeter might fail under load. You need to be reasonably sure the ground will work if ever needed.
 

Last edited by ray2047; 12-05-11 at 08:04 AM.
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Old 12-05-11, 09:36 AM
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please instruct connections; there is no brass screw

Thanks ray...which screws to use as there is no brass? All four are silver...two of those connect and the black bx wires.
Thanks ...pdoyle.
 
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Old 12-05-11, 09:54 AM
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Originally Posted by pdoyle View Post
Thanks ray...which screws to use as there is no brass? All four are silver...two of those connect and the black bx wires.
Thanks ...pdoyle.
Sounds like somebody replaced the screws on the receptacle. We are talking about a receptacle aren't we? Replace the receptacle. I could tell you how to use the current receptacle but I think it is better to replace it.

Since you have newer armored cable you can replace it with a grounded receptacle. Either use a self grounding or a self grounding (regular) three prong receptacle. If you use self ground just ground the NM-b (AKA Romex) cable ground to the box. Otherwise pigtail the NM-b to the receptacle and box.

Above assumes a metal junction box.
 
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Old 12-05-11, 03:10 PM
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sorry but how to wire replacement receptacle?

thanks Ray but when i replace the receptacle with a grounded receptacle, the existing Bx circuit has only two wires, both are black; how will I know which to connect to the brass, and which to the silver screws on the replacement?

or, if I keep the existing ungrounded receptacle, to which screw (there are only silver screws; there is no brass screw) do i attach the white, and the black, wires of the new fixture i'm adding off the receptacle?

thanks
pdoyle
 
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Old 12-05-11, 03:27 PM
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One of those blacks should be white. One way to find out is take a meter and check for voltage between each of the wires and ground (the metal of the cable). You should get 120V on one wire and zero on the other. The 120V would be connected to the brass screws.
 

Last edited by ray2047; 12-05-11 at 03:44 PM.
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Old 12-05-11, 03:47 PM
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And paint the wire that is not a 120v to ground white or wrap with a couple of bands of electrical marking tape.

if I keep the existing ungrounded receptacle, to which screw (there are only silver screws; there is no brass screw) do i attach the white,
White to wide - Black to narrow but I would recommend replacing the receptacle since some one has replaced the original screws. Make it a lot simpler the next time someone works on it to have correct screw colors.
 
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Old 12-05-11, 04:16 PM
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thanks for the solutions! appreciate it greatly!

wish I could mark this as "helpful!" but don't see how to do that...
this is just the information I need to complete the job.
thanks very much!
pdoyle
 
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