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Old 05-07-2010, 08:31 AM   #1
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Junction Box Help/correct way


I have placed a junction box in my attic, where I am connecting some old power to some new lights and so forth. Just want to make sure I connect everything correctly. Going into the junction box I have one old cable that has the wires enclosed in the metal armor. I am also connecting two new wires (NM) 14/2's. The two new wires I have the correct clamps that screw tighten down to secure the cables. My question is, what do I need to hold the metal cable in place going through the knock out hole into the box? Does it also need a piece that goes into the casing to protect the actual wire? Lastly, how should I do the grounds? Do all the grounds get connected together and then also connect to the actual box? Just want to make sure its done correctly. Thanks,
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Old 05-07-2010, 09:10 AM   #2
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Quote:
Originally Posted by bfan781 View Post
I have placed a junction box in my attic, where I am connecting some old power to some new lights and so forth. Just want to make sure I connect everything correctly. Going into the junction box I have one old cable that has the wires enclosed in the metal armor. I am also connecting two new wires (NM) 14/2's. The two new wires I have the correct clamps that screw tighten down to secure the cables. My question is, what do I need to hold the metal cable in place going through the knock out hole into the box? Does it also need a piece that goes into the casing to protect the actual wire? Lastly, how should I do the grounds? Do all the grounds get connected together and then also connect to the actual box? Just want to make sure its done correctly. Thanks,

The metallic cable IS (most likely) your ground. It has to be clamped to the box. Then, all of the grounds from your NM connect to each other AND to the box via a short length of ground wire that is screwed to the back of the box with a ground screw.

So if current got into one of your NM ground wires, the electricity would travel down the NM ground, to the short wire, to the ground screw/box, to your incoming metallic-sheathed cable, to the panel.
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Last edited by secutanudu; 05-07-2010 at 09:15 AM.
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Old 05-07-2010, 09:30 AM   #3
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Everything depends on what type of armored cable you have. They make specific (listed) connectors for armored cables.
You are supposed to use the right connector. If it were me I would use a metal two screw connector just like used for Romex (NM). They hold real good and tight. Make sure you connect all the ground wires to the box if it's metal. Connect one wire to the box and wire nut the rest of the grounds to it.
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Old 05-07-2010, 09:43 AM   #4
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There are similar connectors for metallic sheath cable that look like the connectors for NM cable. The difference is the end is more closed to retain the insulating bushing, typically called a "red head".

Type AC cable requires the use of the red heads.
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Answers based on the National Electrical Code. Local amendments may apply. Check with your local building officials.
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Old 05-07-2010, 12:48 PM   #5
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You need a clamp like this.


Last edited by joed; 05-07-2010 at 12:50 PM.
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