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How to Install New Wires

Jim Mallery | Improvement Center Columnist | July 25, 2011

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Doing your own home wiring can save incredible money, and shocking as it may seem, it's not that difficult.

But there is inherent danger with electricity: A mistake could burn your house down or shoot a load of household current through your body. If you are a little queasy at the thought of rewiring a home, you should consider hiring your local electrician.

Electrician rates vary widely, but generally charge between $50 and $100 an hour. On big jobs, like rewiring a home, a rough cost estimate is $100 per fixture/receptacle. You can do the same job for pennies on the dollar. One property owner in the Seattle, Wash. area had estimates of $23,000 to rewire the house; he did the work himself for under $2,000.

Here are some tidbits to know about a simple wiring project.

Home wiring details

1. If you are adding wires, you probably need a permit. (You don't need permits to replace light fixtures or broken switches.). Call your local building or planning department to see what jurisdiction in your area handles electrical and whether you need a permit. Ignoring a permit is breaking the law, and if a fire results from your work, good luck collecting insurance.

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2. Lighting is usually on 15-ampere circuit breakers, and receptacles are on 20-amp breakers (though some receptacles may be on 15 amps). Twenty-amp circuits require at least 12-gauge wire, while 15-amp circuits can use 14-gauge wire (the smaller the number, the heavier the wire).

3. There are limits on how many wires can go into and out of a junction or receptacle box - the complicated formula is guided by wire size and the size of the box. The guidelines for box fill are easy to find online.

4. Most of the time, you will be using three copper wires (white, black and a bare ground) that are sheathed together. Always connect black to black, white to white and ground to ground. You might have an exception, especially in lighting circuits, where a white wire is connected to black. In that case, the white wire should have black electricians tape wrapped around the end to indicate that it is considered black and is connected to black at the other end. Black is the "hot" wire (line) and white is neutral.

5. Connections have to be inside a box: they cannot be exposed. The box needs to be visible and accessible, so if you splice into wiring in the attic, the boxes must be above the insulation. Metal junction boxes require a ground wire to be attached to the green ground screw in the box. Metal boxes also must have clamps on the wires where they enter and exit the box.

6. Wires are connected with wire nuts. A good electrician will never reuse wire nuts, as the metal threads can lose their grip.

7. Electricians leave about six inches of wire sticking out of the receptacle box, making it easy to attach the receptacle.

8. All air passages where wires travel through studs and plates must be plugged with foam or insulation.

Costs involved

  1. Permit: This can vary wildly, depending on which state and jurisdiction, but even a small job could cost $50 or more
  2. Wire: $20 per 25 feet of 12 gauge
  3. Wire nuts: $2.75 for pack of 25
  4. Receptacle: $5 for tamper-proof, which now are required in most areas
  5. Receptacle box: $2
  6. Voltage tester: $10 (to check for live wires)
  7. Fish tape: $10 (to help you run wire through walls)
  8. Wire stripper: $2 (strips outer sheathing off the wire)
  9. Book on DIY wiring: $15 to $20

Because of the danger if done wrong, home wiring can daunt the DIYer. If you are unsure of yourself, call the local electrician. But if you are knowledgeable about electricity, save yourself a lot of money and run your own wires.