Copper wire, with the insulation intact, can last 100 years and longer if left undisturbed and in a dry location. The age of the wiring itself does not usually cause problems, but the things that have happened to it since the home was built can make the wiring inefficient and, as a result, raise your electric bill in several ways: 

1. A house with 60 or 100-amp service from the 1950s or earlier were not designed for the higher electricity usage of today. Kitchen circuits, in particular, were not intended to be connected to multiple countertop appliances. Large window air conditioners plugged into a regular wall receptacle are another example. The wiring is undersized for the amperage of the appliances, which raises the resistance to the flow of electricity and costs more.
2. Squirrels or rodents in the attic gnaw on wires, which creates hot spots and sometimes arcing, both of which will raise your bill and are a safety problem.Also, people climbing around in the attic and moving boxes around can damage wiring over time, especially near attic hatch openings, like below.
3. Many homes built before 1950 have wiring with cloth insulation that becomes brittle and flakes off with age. The knob-and-tube wiring (see What is "knob and tube" wiring?) at the top of this page is one example, and another one is shown below inside a panel. Deterioration of the insulation creates potential for arcing and electrical leakage.
4. Faulty wiring, switches, and receptacles added over the years by a handyman or homeowner can have excessive resistance at the connections and overly long circuit runs, both of which increase electric usage.
5. Moisture intrusion from a long-term roof or wall leak, or a flooding event, corrodes electric connections and fixtures—again, reducing efficiency and safety.

    A licensed electrician can advise you on any uprgrades of your wiring that might be necessary to improve the system’s efficency and safety. And, although all of these problems with older wiring may increase your electric bill, other defects may be the culprits. See our blog post What could cause an extremely high electric bill? for more.

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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 is undersize electric wiring in a house dangerous? 

• What causes flickering or blinking lights in a house?

• 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?  

    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.