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How dangerous is old electrical wiring?

Friday, September 21, 2018

“Is the old wiring going to burn down this house?” rates as the most often asked question when we inspect a home that’s 50-years old or more. Decrepit wiring with frayed insulation is visualized as the bugaboo hiding behind the walls, ready to start a middle-of-the-night fire. But, while original wiring can possibly be a problem in pre-1940 homes, the bigger issue in all older homes is an electrical system that was not designed for the increased load imposed on it by today’s lifestyle. 

   The post-World War II economic boom began a continually expanding growth in popular, electricity-guzzling home appliances. Wiring designed to support a refrigerator, radio, and a few lights began to accumulate extras, like a black-and-white television, electric range/oven, washer, dryer, wall air conditioner, dishwasher, chest freezer, and a cluster of new-fangled kitchen countertop appliances. 

    The futuristic world of push-button gadgets that got laughs in the 1960s Jetsons cartoon show gradually became a reality as even more appliances became must-haves, such as central air conditioning, a microwave oven, big-screen color TV, desktop computer, stereo system, personal hair dryers, jacuzzi tub, exercise treadmill, and dad’s power tools in the garage. Electricity use has increased at a rate of about 5% per year for the past 30 years, and each new year puts additional demands on an old home’s wiring.

   Also, the lack of wall receptacles in an older home, due to the low level of use of the era, contributes to the problem. Often there is just one receptacle in a bedroom and none in the dining room, for example. So homeowners make do by using extension cords strung around the perimeter of rooms or, even worse, under rugs to get power to where they need it.

   Plus, the average electric service in a 1950 home is 100 amps. An amp, short for ampere, is a measure of the working power that can be delivered to the home through its electrical system. Most new homes require 200 amps, double the old standard.

    The undersize electric service of an older home is safeguarded by circuit breakers that are supposed to trip when too much current is flowing through any circuit, but circuit breakers are mechanical devices with an approximately 40-year life. When they cease to functional properly, circuit breakers don’t shut down or give any outward sign of failure. Instead, they simply no longer trip when the wiring is overloaded. Many older homes have the original electric panel and breakers still in place.

   Then, add to this mix a few badly-done homeowner electrical repairs over the years and the likelihood of a problem soars. While we note many of these defects during a home inspection, some safety issues—such as whether the circuit breakers are still functioning properly or the condition of wiring inside the walls—are beyond the scope of our inspection. But there are a number of things you can do, short of replacement, to make the electrical system of your older house safer:

•• Extension cords are meant for temporary use only. Ditch them anywhere they are permanently installed, and have a licensed electrician run wiring to additional new receptacles.

•• Replace any damaged switches and receptacles. Also, change out any receptacles that can no longer securely grab the prongs of an appliance cord. This is most likely to occur at  locations where cords are repeatedly plugged in and out, like at the kitchen counter. A loose connection between receptacle and cord can cause arcing. Any receptacle where an electric cord can be pulled out with no resistance should be replaced.

•• Consider replacing the old 100-amp panel with a new 200-amp one. The change-out will require an electrician to run new service wires to the home. Because new panels are required to have special AFCI breakers for most circuits, you gain an added level of protection for the aging wires still in the wall. Arc Fault Circuit Interrupter breakers sense when any wiring in the circuits they protect is frayed or otherwise damaged  and arcing/sparking is occurring between two disconnected pieces of the same wire or two adjacent wires in a cable—and they cut off the power to the circuit.

•• Have an electrician replace the breakers in the panel if replacing the panel is more than you can afford. The panel box typically has a longer life than breakers anyway, and you will get AFCI-breaker protection for the 120-volt general purpose circuits. The only problem with this strategy is that it’s hard to find replacement breakers for some old panels.

••Shut off the circuit at the panel and call an electrician at the first sign of an electrical problem, such as lights that blink, appliances that work intermittently, breakers that keep tripping, or the acrid, burning smell of a short circuit.

•• Look for evidence of amateur electrical repairs and have a professional electrician fix it.

   Insurance companies are concerned about the safety of electrical systems in old homes too, and almost always want a 4-point inspection report by a licensed contractor or home inspector, that includes an evaluation of the electrical system, before issuing a policy. Some insurers even want a separate electrical inspection, signed off by a licensed electrician, in certain circumstances. If the electric panel has screw-in type fuses (like in the photo at the top of this blog), you will have replace it with a new circuit-breaker panel in order to get homeowner’s insurance nowadays.

    But don’t let electrical safety worries scare you away from considering the purchase of an older home. One third of the homes in America are over 50 years old, and they are often located in desirable neighborhoods. Many are also a good value. Just be sure to get it evaluated by a licensed home inspector and make any recommended electrical safety upgrades once you move in.

    Also, see our blog posts What causes flickering or blinking lights in a house? and Why is undersize electric wiring in a house dangerous?  

• • • • • • • • • • • • • • • • • • • • • • • • • • •

Here’s links to a collection of our other blog posts about ELECTRICAL WIRING:

Which house appliances need a dedicated electrical circuit?

Can a short circuit cause a high electric bill?

What is the maximum spacing requirement for securing NM-cable (nonmetallic-sheathed cable)?

Is it alright to just put wire nuts on the end of unused or abandoned NM-cable or wiring?

What causes copper wires to turn green or black in an electric panel?  

What are typical aluminum service entrance wire/cable sizes for the electrical service to a house?

Why is it unsafe to bond neutral and ground wiring at subpanels?

Should I get a lightning rod system to protect my house?

Why is a strain relief clamp necessary for the cord connection to some electric appliances?  

Does a wire nut connection need to be wrapped with electrical tape?

What is the minimum clearance of overhead electric service drop wires above a house roof?

What are the requirements for NM-cables entering an electric panel box? 

What is the color code for NM cable (Romex®) sheathing?

Why are old electrical components not always "grandfathered" as acceptable by home inspectors?

How can I find out the size of the electric service to a house?

Can old electrical wiring go bad inside a wall? 

What is an open electrical splice?

What are the most common electrical defects found in a home inspection? 

What is the life expectancy of electrical wiring in a house? 

What is an "open junction box"? 

How dangerous is old electrical wiring? 

What is a ground wire? 

I heard that aluminum wiring is bad. How do you check for aluminum wiring?  

What is "knob and tube" wiring?  

What is the code requirement for receptacle outlets in a closet?

   Visit our ELECTRICAL page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.

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