Finding an Electrical Source

• Fishing Wiring in Walls
• Splicing Wires
• Measuring Circuit Amps
• Wiring Behind Baseboards

A new receptacle or switch can usually be added in the wall space between studs using an "old work" outlet box but a new ceiling fixture will require some support. See Installing a Ceiling Fixture for help.

Always turn off the power before working on electric circuits and check local electrical codes before altering wiring. This page offers some options for locating a source for a new electrical outlet. Use the methods on the next page to cut holes and fish electrical cable through walls and ceilings for a new light fixture or wall receptacle.

Household wiring in the US is color coded as follows: Black and red are hot, meaning the electricity come through these wires first. The white wire is the neutral wire. It carries the electricity back to the service panel where it is shunted to ground. The green wire and in the case of NM cable, the bare wire, are ground wires. These are safety wires that carry electricity immediately to ground in case of a short.

When running new cable pay attention to the amp rating for the circuit you are extending. For a 15 amp circuit, use 14 awg (american wire gauge) cable. For 20 amps use 12 awg, 30 amp: 10 awg, 40 amps: 8 awg, 50 to 60 amps: 6 awg.

Finding an Electrical Source for a New Outlet

Decide on the location of the new electrical fixture and where the source will be. When choosing an electrical source, it will always be OK to extend a circuit from an existing box with no more than one cable running to it, as long as the total electrical draw from the other outlets in the circuit doesn't exceed the ampere rating. To determine the load of the circuit, use the chart and formula for measuring amps in a circuit on this page.

If you want to use a source with more than one cable currently installed, check the wire splicing page for limits on the number of wires that are allowed in one outlet box. If adding another cable to the box is not possible, it may be possibe to split the source cable before it enters the box. If there's enough slack in the cable a junction box can be added to splice the new outlet into the circuit. The junction box must remain accessible, so look for a spot where the cover plate will blend. Use a 3 x 2½ inch device box at the same level as wall receptacles to minimize visual impact.

Planning the Circuit

Determine inside of which walls and ceilings the cable must be run. For example, with a new ceiling fixture using a source from an existing wall receptacle, the cable will have to be run inside the wall cavity, through the wall header and into the ceiling cavity to the new fixture. Or if you are using a receptacle on an upper floor to serve a ceiling fixture below, the cable would have to be run through the sole plate and flooring and into the ceiling cavity below.

There will probably be several options for a electrical source for a new outlet. Below are a few of the most common. Often a ceiling fixture can be used as the source for a new outlet if the wiring at the fixture has a hot wire that is always on. That is, one not controlled by the fixture switch. Alternately a wall receptacle from an upper floor can be used as source for a new ceiling fixture but a switch loop must be run to a wall switch in addition to fishing the cable from the source.

In the example below a new wall receptacle can be installed using an existing receptacle in an adjacent room. This can often be the easiest way to access a source for a new receptacle.

In a room with old plaster of at least ¾ inch thickness, an armored cable or greenfield can usually be run under the baseboard. Remove the baseboard and chisel a channel along the floor wide enough to bury the cable flush with the plaster. The armored cable or greenfield will protect the wires from nail punctures. This method will not work with ½ inch drywall. At least ¾ inch of wall material is needed to bury the armored cable. For ½ or ⅜ drywall use the method for adding a new electrical wall outlet behind baseboards on this page.