200 year old house, very thin walls, outlet box question

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Old 01-17-11, 08:41 AM
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200 year old house, very thin walls, outlet box question

I want to replace an outlet in an existing interior wall. The wall is very thin being a sandwich of plaster, lath, 1" plank, lath and plaster Overall it is about 2 3/4" thick or slightly thinner. The outlet there now does not sit flat on the wall. Are there shallow outlet boxes available ? If so what is the shallowest I can get ? Is there another method to close up the gap between the back of the oulet cover plate and the wall ?
 
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Old 01-17-11, 10:52 AM
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Boxes are available in different depths though I'm usually going for the deepest available so I don't know how thin are the thinnest.

I have used box extensions which screw onto the face of the box, making the box deeper. You then mount your outlet & cover plate to the extension. It helps if you paint the extension to match your walls before you install it.
 
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Old 01-17-11, 10:57 AM
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There are boxes that start at 1 1/2" deep, but you need so much cubic inch capacity based on the number of conductors and devices in the box so your choices may be limited.

Can you supply the number and sizes of cables in the box? Also is the wiring method metallic or non-metallic? Are there clamps in the box to hold the cables in place?
 
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Old 01-18-11, 07:53 AM
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It's not a matter of enough interior space in the box. The box cover does not sit flush against the wall because the box sticks out about 1/4" from the wall.
 
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Old 01-18-11, 07:59 AM
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I believe the wire is 14 gauge, possibly 12, braided sheath surrounding the 3 wires. It is definitely 2 conductor with a paper wrapped ground wire which, I was dismayed to discover, is not attached to anything. The outlet itself is an old style non-grounded two prong receptical. There is a cable clamp at the bottom of the box where the cable enters the box. I measured the box to be 1 7/8" deep from the interior surface of the back to the front edge where the cover goes.
 
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Old 01-18-11, 08:35 AM
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It may just be that the clamp screw is preventing the box from dropping far enough into the wall.

What I was referring to about minimum capacity is that the code requires so much capacity per conductor. You cannot install a box with less space than is allowed.
 
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Old 01-18-11, 10:29 AM
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I'll check on the clamp screw. I will also look into what the code requirement is in this area for a two conductor wall plug box. Thanks for your help.
 
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Old 01-18-11, 11:32 AM
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Generally it is not mandatory to do so, but it is a good idea to install a GFCI receptacle on ungrounded circuits.
 
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Old 01-18-11, 11:34 AM
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How opposed are you to a surface mount box?

It is definitely 2 conductor with a paper wrapped ground wire which, I was dismayed to discover, is not attached to anything
I would sugest measuring voltage beteen this ground wire and the black wire. If you get 120v you may be able to "modernize" this receptacle while you are working on it. If no significant voltage Ben's idea of a GFCI would give you more personal safety.
 
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Old 01-19-11, 10:43 AM
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OK, I tried to find a copy of the NEC. Is there a link available to get a free copy or is it only possible to purchase it ?
 
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Old 01-19-11, 11:34 AM
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I think the NFPA has a limited "free preview" link on their website, but the code book itself is not free. I would think that most libraries or town halls would have a copy you could check out. Is there something specific you need to know? One of us can probably look it up.
 
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Old 01-19-11, 04:15 PM
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Thank you ipbooks, for the suggestion.
A quick rundown on what the NEC calls for regarding how many cubic inches are required in an electrical junction/switch/receptacle box and for what devices and number/gauge of conductors, would be of use to me. I'm sure I've seen a chart of this somewhere online but I have not been able to find it.

I'm tyring to determine if code allows for a 1 1/2" deep box with 2 conductors plus bare ground wire to a duplex receptacle. Will there be enough cubic inches contained ? "pcboss" alerted me to the fact that this is a consideration. I looked and the clamp is not preventing the box I have from going all the way into the wall. The box is backed up tight against the lath on the other side of the wall. I'm hoping to avoid using a surface mount box. I'm thinking a deeper cover (like one for an exterior box might do the job) but again, not sure if there is a code that covers this. The other end of the bare (paper-wrapped) ground wire is connected to it's counterpart 10 feet away, in the junction box that feeds this outlet box.
 
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Old 01-19-11, 05:36 PM
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Here is a calculator. Box Fill
 
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Old 01-19-11, 07:05 PM
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Ray 2047, Thank you very much. I found elsewhere how to determine the number of conductors. The "Box Fill" calculator link you listed, does the job.
 
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