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I have a wall sconce that my wife really likes and wants installed on a brick wall. The sconce she purchased is designed to sit on top of a wall box that has been prewired. I don't want to install this in the brick, so my idea is to hook up the wires to a standard ac plug and wire, then run it under a cable cover.

The light has one black, one white and one ground cord. When I cut off the end of an old AC wall cord, will I find the same connections? If not, how do I connect the cord safely? Is this a terrible idea in general?

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Is this indoors or outdoors? –  wallyk Sep 4 '13 at 15:09

3 Answers 3

up vote 3 down vote accepted

Portable lamps (at least in the US) are generally designed without a ground wire. The bodies of the lamps, even if metal, are designed not to be likely to be prone to a short to the hot lead. The standard lamp cord is therefore two wire (hot and neutral). Most modern lamps are polarized, meaning the cord/plug is designed to ensure that the hot lead is attached to the hot side of the outlet.

Sconces and other lamps that are intended for fixed mountings on electrical boxes have a hot lead, a neutral and a ground. The ground is the safety measure in case of a short.

When you convert a fixture intended for use with a ground wire to a plug-in setup, you need a grounded cord to preserve the safety factor. The simplest way may be to buy a grounded extension cord, cut off the socket end and splice the cord with the plug (male) end into your fixture.

Attach the hot lead to the black wire of the fixture, the neutral to the white (the neutral wire is attached to the larger blade of the plug and the casing is sometimes ridged), and the ground to the green (or bare).

You can then run the cord under a cord cover to a conventional grounded outlet.

P.S. Be sure to use a bushing or something similar to prevent any cord/cable from being pulled through and cut or frayed by metal edges at the point where it exits the fixture or metal cable cover.

CAUTION

This whole discussion assumes that you are installing this permanently (a wall fixture is not well protected at the back from damage or short) and on an interior wall. Exterior fixtures are specifically designed to attach in an exact way to exterior boxes to ensure that they are water resistant. Any compromise of that attachment mechanism may lead to leakage, shorts and danger of electrocution or fire.

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Great answer, thanks! –  coneybeare Sep 4 '13 at 3:43
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This is not safe. If the fixture was meant to be attached to an electrical box, it's likely not a weatherproof fixture on its own. Installing a non weatherproof fixture outside is not a good idea, especially when said fixture is cobbed together with an extension cord. –  Tester101 Sep 4 '13 at 12:30
    
@Tester101 Excellent point. I assumed he was talking about an interior brick wall. Will add a caution. –  bib Sep 4 '13 at 12:38
    
@bib Yeah I just thought maybe it's not outdoors. However, you still have the potential of exposed metal parts. Fixtures designed to be attached to boxes, should be attached to boxes. –  Tester101 Sep 4 '13 at 12:40
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This is for an indoor wall. –  coneybeare Sep 4 '13 at 15:43

The answer is likely, NO.

When fixtures are designed to attach to an electrical box, they typically require that box as part of their weatherproofing, or to contain connections/hide exposed parts. Without the box the fixture is likely not weatherproof, and connections and/or electrified parts may be exposed. Installing a non-weatherproof fixture in a wet, or damp location is not a good idea (and is likely against local codes). Installing any electrical fixture in a way it is not designed for, could lead to trouble. Not properly containing splices and/or junctions is bad practice, and may be against local codes.

While attaching a modified extension cord to the fixture, will surely provide power to the fixture. It's probably not the safest, or best approach.

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It will be indoors, against a non-conducting brick wall. I will use electrical tape to surround the connections, then perhaps put extra around the entire backend of the unit. Do you think that would be enough? –  coneybeare Sep 4 '13 at 15:42
    
@coneybeare No. As bib pointed out in a comment, you'll have to manufacture a back cover, then submit it to UL for testing. The fixture is designed to be attached to an electrical box, and I'm sure the manufacturers installation instructions say to attach it to a box. This means the only valid installation method, is to attach it to a box. See also, my favorite code section "110.12 Mechanical Execution of Work. Electrical equipment shall be installed in a neat and workmanlike manner." –  Tester101 Sep 4 '13 at 15:45
    
@coneybeare I was actually being a little facetious. Tester101 is right that installation of a fixture other than on a box might not meet code and might be objected to by an inspector. However, depending on the construction, it may be possible to attach it in a workmanlike manner. You need to gauge the devices, the attachment mechanism and your skill. –  bib Sep 5 '13 at 20:15

No, you should not use a lamp cord to power a sconce. It is unsafe, unprofessional-looking, and against code.

What you're looking for is a surface-mounted electrical box. You screw it into the brick, and run conduit (also screwed to the brick) from the nearest electrical connection to it. You run the electrical wires through conduit to the surface-mounted box, then mount the sconce to the box.

Surface mounted box
(image taken from above link)

Bring the sconce and ask the people at Home Depot (or your country's equivalent store), and they'll be more than happy to show you what you need to buy.


Also: you mentioned splicing electrical wires using electrical tape in the comments. This is not allowed. You should be using electrical wire nuts if you are in the US. All the splicing will be done inside the box, where it is easily accessible but out of sight.

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