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How To Add An Additional Electric Line For A Portable Heater

by Sara Cook

Many houses have rooms that remain cold, even though the rest of the house is comfortably heated. A portable electric heater is a good solution to the problem, but you may run into difficulties with tripped circuit breakers or blown fuses if it is plugged into an existing line.

Many portable heaters use up to 1500 watts of electricity, which is near the maximum capacity of a 15 amp line. If you check the breaker that controls power to the outlet you intend to use, you will see either a 15 or 20 amp breaker (the number is stamped on the breaker itself).

If you intend to plug into a 20 amp line, you should be safe if no other high powered appliances are used simultaneously with the heater. However, if it is a 15 amp line, you will need to add an additional line for the heater.

What you will need:

An outlet and cover plate

If the heater will be used in a damp location such as a bathroom or basement, you will need a GFCI (Ground Fault Circuit Interrupter) outlet, which shuts off power if it detects faulty grounding and protects users from electric shock. If you use a GFCI outlet, you will also need an open face plate to access the reset button in the middle of the outlet.


You will need a 3 wire sheath of 14 gauge wire, with the length needed determined by the distance from the proposed outlet to the circuit breaker box. Add several feet to that measurement to allow for wiring and connection purposes.

Old work outlet box

Designed for use in existing walls, these outlet boxes have small flaps on opposite corners that open inside the wall to secure the box to the wall.

15 amp circuit breaker

You will need to buy a breaker that fits your breaker box, so check the box's manufacturer's label, and buy the same brand of breaker. One size does not fit all in this case.


  • Wire cutter/stripper tool
  • Flat and philips head screwdrivers
  • Utility knife or hole saw for cutting hole in drywall or other surface material
  • Drill with 12" long 3/8" diameter bit


Wire nuts and electrical tape

Preparing to install the outlet

Begin by tracing the outline of the open portion of the outlet box at its intended location, then cut out a hole along the trace marks. Break off one of the punch out holes on the bottom of the outlet box, then place it inside the wall. Tighten the two securing screws on opposite corners until the box is tight inside the wall.

Before beginning to feed the wire sheath into the outlet box punch out hole, you must carefully examine the route that the wire sheath must take to reach the breaker box. If you are fortunate enough to have a direct line to the breaker box, you can feed the line to a hole that you will pre-drill in the ceiling near the breaker box.

However, if you must travel a more circuitous route to the breaker box, you should consider buying a wire fish tape, which is a flat flexible cable on a reel, used to pull wire sheathes through walls and ceilings. Running wire through finished walls is often a deal breaker for amateur electricians, who may give up in frustration when encountering obstructions inside walls.

When you can successfully feed the wire sheath to the site of the breaker box, pull the end of the wire sheath to the side of the box, allowing for an extra two feet of slack for connection purposes.

Installing the outlet

Cut the wire sheath at 12" from the outlet box, then strip one inch of insulation from the end of each of the three wires in the sheath. Connect the black wire to the top gold terminal on the outlet, the white wire to the top silver terminal, and the green or copper wire to the single green terminal, by looping the stripped wire ends around the terminal screws and tightening the screws securely.

Push the outlet into the outlet box, and tighten the upper and lower screws until it is secure, then screw on the cover plate.

Connecting the breaker

Strip the insulation from the three wires at the breaker location. You will then shut off the main breaker to the home. Since you will likely be plunged into some shade of darkness, a flashlight will be useful.

When all power is off, knock out a punch out hole in the side of the breaker box, and pull the three wire sheath through the hole. You may need to separate the wires further by opening the plastic sheath up to 12 inches. 

You will then connect the white and green or copper colored wires to the silver grounding bars inside the breaker box. There will be several holes and securing screws in the grounding bars ,so just take your pick.

The black wire will be connected to the screw terminal at the end of the breaker. Once this is done, punch out an available slot in the breaker box, and push the breaker into the slot until it clicks into place.

To learn more, contact an electrical services company like Narducci Electric

Turn on the main breaker, clean up your mess, and you're finished.