Understanding the Details of Wiring and Receptacles

Shannon Lee

Editor's Note: This is article 4 of 8 in Chapter 7: The Electrical Guide of Old House Web's Home Restoration Guide. This guide was developed and edited for old homes from original materials in the U.S. Housing and Urban Development (HUD) Rehab guide.


Section 1--Overview

Residential wiring has gone through many evolutions since it was first introduced in the late 1800s. Today, most homes contain service wires, transmission wires, branch circuit wiring, appliance power cords, and even extension cords of various lengths and purposes. This particular section focuses on branch circuit wiring, which runs between outlets and circuit breakers.

Understanding the details of wiring and receptacles (or outlets) is directly related to safety. Here are a few wiring situations you might expect to encounter in your old house:

  • Knob and tube wiring. Popular through 1920, knob-and-tube was a two-wire system held about one inch away from studs and joists by porcelain knobs, or protected by porcelain tubes where it crossed other wires or went through the framing. Knob-and-tube wiring contained no grounding and the outlets were not polarized.
  • Wooden raceways. Illegal since the 1930s, wooden raceways might still be found in a very old house. If you do find a wooden raceway--wood molding containing two or three wires--during your home restoration work, remove it immediately.
  • Metal raceways. First recognized in 1907 by the National Electric Code, metal raceways are still used today. These are considered safer than their combustible wood counterparts.
  • Greenfield conduit. Developed in the late 1890s, Greenfield flexible-steel conduits made it easy to snake wiring through the walls and floors.
  • Armored cable (Type AC). Armored cable was developed in the late 1890s but didn't see widespread use until the 1920s. The continuous spiral of galvanized metal provided the only ground in this system; in 1959, the safety of armored cable was greatly improved when a slender aluminum bonding strip was added to create a ground.
  • Non-metallic sheathed cable. This cable contains two insulated rubber conductors surrounded by a sheath of cloth. In the late 1940s, the conductor insulation changed from rubber to plastic and by the 1960s, the fabric sheathing had changed to plastic, too.

Common problems you might encounter in an old house are usually tied to deteriorating insulation or loose connections. Loose or broken connections are usually an easy fix, but problems with insulation can turn into a major rewiring job. Many problems with deteriorating insulation can be attributed to age; for instance, rubber insulation has a life expectancy of about 25 years. If the home was wired before 1930, the rubber insulation is well on its way to becoming hazardous.

There are a few ways to take care of the problems with old insulation:

  1. Complete rewiring. Sometimes a complete rewiring job is the easiest and safest way to solve wiring problems in an old house, including deteriorated insulation and overloaded circuits. The trick is to handle the rewiring with as little disturbance to the ceilings and walls as possible.
  2. Installing raceways. An option for rewiring includes raceways, which securely hold the wiring in metal or PVC channels that are protected by a cap. Less costly than snaking wires through the structure of the house, raceways are more visible, but offer much more flexibility with future changes.
  3. Insulation repair. There are several techniques available to repair crumbling insulation, but check with local code officials to make certain the fixes are acceptable.

Section 2--Fixes for Aluminum Wiring

Aluminum wiring was widely used between 1962 and 1972. The hazards of aluminum wiring include connections with dissimilar metals and the oxidation of aluminum, both of which can lead to electrical resistance. This makes the wires hotter when in use and as a result, creates a fire hazard.

There are three ways to correct the problem during your home renovation:

  1. Rewiring. The safest way to handle aluminum wiring is to remove it altogether and replace it with much safer copper wire.
  2. AMP COPALUM connectors. The only permanent repair recognized by the U.S. Consumer Product Safety Commission (CPSC), these connectors must be installed by an electrician trained in their use.
  3. "Scotchlok" connectors. The CPSC considers these connectors to be the only reliable alternative to the AMP COPALUM fix, but again, installation can only be done by a certified electrician.

Section 3--Safer Outlets

Grounding and polarization are two key elements in a safe outlet system. Grounding protects you from potential electric shock by directing excess currents toward the grounding system, while polarization keeps the hot and neutral wires of an electrical system separate to avoid accidental reversal. In modern outlet systems, polarization is accomplished by making the two prongs in an outlet different sizes to ensure plugs are always connected the same way. Three prong outlets typically have this polarization feature as well as a grounding pin.

In an older house, two-prong outlets (known as receptacles) might not be grounded or polarized. Though two-prong outlets do not have to be replaced in the course of your home renovation, because grounded and polarized outlets are safer, replacement should definitely be considered. There are several ways to make the change:

  1. Rewiring. Running new wiring is the only way to ensure proper grounding. This is especially important where the outlet will be used for powering sensitive electronic equipment.
  2. New ground conductors. A ground conductor that routes back to the service panel or to the closest accessible point of the grounding electrode system is cheaper than a complete rewire.
  3. Check the receptacle box. Test the receptacle box with a circuit tester to ensure it is grounded. If it is, simply add a new receptacle and ensure the grounding connection is secure.
  4. Install ground fault circuit interrupters. If you are going to replace your two-prong outlet but can't ground the three-prong, you can use a ground fault circuit interrupter (GFCI). The GFCI is not grounded; however, it shuts off the current in the event of a ground fault. Keep in mind, however, that this fix means your surge protectors will be useless.

Different lighting fixtures may interact differently with your electrical wiring, so check for compatibility before undertaking major renovations. The next section of the Old House Web Restoration Guide discusses lighting systems.



About the Author

Shannon Dauphin is a freelance writer based near Nashville, Tennessee. Her house was built in 1901, so home repair and renovation have become her hobbies.

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