How Long Does Electrical Wiring Last in a Home?


old wiring

The electrical wiring is an essential part of any home. I often describe it to people as the house’s circulation system.

Buying a newer home will be up to code and may not possess any serious hazards. However, an older home that was built a few decades ago may raise some concerns about its wiring. If you are going to be buying or are currently living in an older home, the condition of the wiring is something that will eventually need to be updated.

How long does electrical wiring last in a home? According to the International Association of Certified Home Inspectors (NACHI), the copper in electrical wiring can last over 100 years; however, the outer protective sheathing will breakdown much sooner. Depending on the type of sheathing often determines the lifespan, which is typically 50 to 70 years.

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However, age is not the only determining factor. There are a lot of details when it comes to the lifespan of your home’s wiring.

In this article, I would like to show you what you can expect to find in a home, warning signs its time to update all or part of your electrical wiring, and how each of the different wiring situations can and will affect you.

How Long Does Electrical Wiring Last?

The average life expectancy of home wiring is about 50 to 70 years. This period of time can be more in some cases. It can also be significantly less than that, depending on the way the wiring is installed, the presence of damage to the sheathing and the number of modifications during the years

Electrical wiring can last a really long time before starting to decompose or deteriorate if it is installed correctly.

On their own, the materials that a wire is comprised of can last a really long time. For example:

  • The copper inside the wires can last over 100 years.
  • The aluminum inside the wires can last between 80 and 100 years.

However, it is not that simple, and we are not placing these wires in perfect conditions.

There’s much more that needs to be considered.

  • Electrical wiring is not always installed correctly.
  • Environmental factors the electrical wiring is installed in may not be ideal.
  • The electrical wiring may be faulty due to unpermitted remodeling, improper handyman or DIY work.
  • Advances in Electrical Safety Codes throughout the years.

All this will affect the weakest link in the chain, which is the protective sheathing or often referred to as the insulation.

The protective sheathing is going to deteriorate and wear out much quicker than the actual wire itself.

And the main aspect that will determine the life expectancy of the wiring is the condition of its protective sheathing.

With time, the insulation will become increasingly more dry and brittle. Eventually, it starts falling apart. This means that we can end up having exposed electrical wires. This creates a major safety issue for both the house and people who may come in contact with the wiring.

Having electrical wires exposed like that is very dangerous. It can lead to:

  • Arcing.
  • Electrical fires.
  • Electrical shocks.

What Materials Are Used in Wiring Manufacturing?

wiring

Wires can be made from different materials. It is a good thing to know a little bit more about each of the most commonly used materials. They all have different advantages and disadvantages.

This is important, especially for future homeowners and homebuyers as it may play an important role in the purchasing process because some wirings come with significant drawbacks.

1. Copper Wiring

Copper is the most widely used material for wire manufacturing today.

A few qualities that are specific to copper are making it the go-to metal.

  • First, it is an excellent conductor and transfers electricity with ease.
  • Second, copper wires are easy to bend and place in different spots in the house.
  • And, copper is also a reasonably easy metal to mine and extract. It is not as abundant as some other metals, but the relative ease of finding it is making it a good option.

2. Aluminum Wiring

Aluminum is more abundant in nature than copper. This is making it cheaper compared to other metals.

One of the downsides of aluminum is that it is not as good of a conductor as copper is. Technically, you will need wires with a bigger diameter in order to carry the same electricity a copper wire does.

For example, to have the same conductivity as a copper wire with a cross-section of 100 mm, the aluminum wire will have to be about 156 mm.

Aluminum wiring can be dangerous in older homes that were built during the 1960s and 1970s.

An investigation carried out for the U.S. Consumer Product Safety Commission (CPSC) concluded that older homes built before 1972 (that had aluminum wiring) are 55 times more prone to electrical fires. The investigation looked only into the wire connections at the outlets. So these rates may even be higher.

There were no official investigations and statements about homes built with aluminum wiring after 1972.

The reason why many homes built in that period may have aluminum wiring is that the U.S. was going through some severe copper shortage at the time.

This led to a lot of manufacturers switching to the more abundant aluminum for their wiring and in some cases even for the production of electrical panels and breakers (which is the case with Zinsco electrical panels).

The main thing that is making aluminum wiring dangerous is not necessarily the wiring itself. But instead the connection points (The places where the wire connects to any switches, receptacles, junction boxes, panels, and more).

  • The problem with aluminum wiring is that when electricity passes through the wires, it generates heat. The heat will cause aluminum to expand as it gets hotter and contract when it cools off. Eventually, this causes the wiring connections to become loose. A loose connection like this can cause arcing, which can start an electrical fire.
  • Another problem comes from the diameter of the wires. The wires installed during that period were of a smaller diameter. And they cannot carry the electrical current that a copper wire with the same size can. This and the increased electrical demands we have nowadays can lead to overheating of the wires creating a serious electrical fire hazard.

Some stranded aluminum wiring is still used in houses today for the main service entry wires and other 240 volt circuits like ranges and clothes dryers.

Federal Pacific Stab-Lok breaker panels were also known to have solid aluminum branch wiring. If you have a Federal Pacific panel in your home, our article Are Federal Pacific Breaker Panels Safe? Dangers & Cost to Replace we discuss some of the main problems concerning these panels.

3. Alloys and Silver Wiring

Different alloys from aluminum and copper and silver are also used for electrical wire production. They are usually used in the industrial sector, so they are not found in residential buildings.

Silver is considered to be the best conductor. However, its high cost often is making it not a suitable alternative, especially when copper and aluminum are way cheaper and more readily available.

The Different Types of Wiring

old house electrical

In addition to the materials used for the manufacturing of the electrical wires, there are also some inherent problems that we may face with the different types of wiring.

Throughout the years, different types of wiring practices were used, and wires came with different kinds of insulation.

Knowing and being able to recognize these may help any new homeowner in identifying potential hazards and points of concern.

1. Knob and Tube Wiring

Although they are grandfathered into the electrical code, knob and tube (K&T) wiring is considered by industry professionals as dangerous and unsafe. Most of the K&T wiring can be found in homes built between the 1880s and the 1940s.

The ceramic tubes are really durable and can last many years if not damaged in any way. However, the wiring and its insulation, in particular, are subject to natural wear and tear. Also, rodents and other animals may try to chew through the wires.

The main disadvantages of the K&T wiring are:

  • Insulation becomes brittle with time. K&B wiring was considered the top of the line before. However, there is no way of getting around the fact that this type of wiring is extremely old. Even if the wiring appears to be working fine now, there is no guarantee for how long it will be able to continue doing that.
  • The wiring needs to breathe, so adding insulation over it is not recommended (it is even strictly forbidden by the National Electric Code (NEC) since 2008). Some electricians say that if the wires are touched or disturbed in any way the entire wiring needs to be replaced.
  • K&B wiring doesn’t have any grounding, which can lead to higher risks of electrical shocks.

It usually is not permitted to extend or modify the wiring in any way. This can leave homeowners with electrical wiring that is not really suitable for the higher electrical needs we have today.

Electronic devices buildup static electricity. Without proper grounding, this makes the circuit susceptible to lightning strikes. Many older homes have lightning rods on the roof of the home that was grounded by aluminum wiring to a grounding rod for this very reason.

2. Cloth Sheathed Wiring

Cloth wiring is another very tricky topic for a lot of home inspectors, electricians, and insurance companies.

Cloth sheathed wiring is usually frequently found in home properties that were built before 1970.

One of the main problems with cloth wiring is going to be its age. Although considered by a lot of people safe the insulation will become brittle with time, the cloth can become frayed, too. As both the rubber and cloth are wearing down, this can lead to arcing and electrical faults.

Some common problems that can be found with cloth sheathed wiring:

  • They pose a fire hazard due to the insulation becoming brittle and possibly falling apart.
  • Below the cloth sheathing was a layer of paper insulation.
  • Most cloth sheathed wiring doesn’t have a grounding wire.
  • Wires may become hot and expose surrounding areas to heat.
  • Cloth sheathed wiring is known to contain asbestos, which is a known carcinogen.

3. Plastic Sheathed Wiring

Polyvinyl Chloride (PVC) is one of the most widely used materials for cable production. However, due to some health, safety, and environmental concerns, it is becoming less popular.

One of the dangers of PVC wiring is that if there are a lot of wires confined in a small area, this may lead the wires to overheat.

  • The PVC sheath can burn in that case.
  • Another thing is that when burning PVC is releasing toxic fumes.
  • PVC is not suitable for recycling.
  • Some PVC sheathed wiring lacks a grounding wire.

4. Non-Metallic (Romex) Wiring

Non-metallic (NM) wires are one of the most widely used types of wires. They can last a really long time because of the heavy insulation they have. An NM wire consists of a hot, neutral and ground wire, each of which is individually insulated. And then all the wires are insulated together with one more layer of PVC plastic.

This is making them overall very durable and very flexible and easy to install.

5. Armored Wiring

Armor Clad (BX) wiring are very similar to the NM cables. The only difference is that the wires are insulated and covered by a flexible spiral made from aluminum or steel.

The BX wires are extremely durable and can last a really long time. They are relatively easy to install.

The only downside is that they are significantly more expensive than an NM cable.

Is Old Wiring Dangerous?

One of the main things that need to be checked is the age of the wiring. If it is an older property that has never had its wiring updated or replaced, this may mean that the wiring is very old.

In some cases, even wiring that has been installed 25 years ago can be considered outdated and up for replacement.

Old wiring frequently comes with some risks.

  • If the wires have compromised or frayed insulation or the wires are exposed, there is a chance we can get in contact with them. This can lead to various electrical faults, electrical shocks, and electrocution.
  • Worn out cables or loosely connected and faulty wiring can lead to arcing, which is known to produce tremendous amounts of heat. This will expose the surrounding areas and the cables themselves to high temperatures, from which an electrical fire can start.
  • Older wiring has higher chances to have been modified by previous inhabitants in a DIY style. Today the wiring system in the homes have to comply with a lot of rules. And if the wiring is really old, there may be a higher chance that over the years people have tried to modify it and adapt it to their needs. And the wiring may not be code compliant or even safe anymore.
  • Older wiring was installed with lower amperage in mind compared to the requirements of today’s electrical appliances. This may lead to many, if not all, of the electrical circuits in an older home to be easily and quickly overloaded. This is one of the biggest concerns when it comes to older homes.

What Is the Average Cost to Rewire a House?

Replacing the wiring in any building is a costly endeavor.

So what is the average cost to rewire a house? The average costs to rewire a house can vary widely, mostly due to the size of the house and the number of circuits the house has. This cost can be anywhere from $9,000 to $11,000 for an average-sized home up to 1500 square feet.

It’s virtually impossible to give a hard number here as several factors that affect pricing exists. The exact amount will vary from property to property. It is recommended to get at least a few quotes from licensed electricians before settling for a particular one.

Some of the factors affecting the cost to rewire a house include:

  • Upgrading the service entry wires, meter base, service mast, and weather head.
  • The number of circuits will increase as in older houses circuits often covered multiple rooms. Current electrical codes require circuits for each room and, in some cases separate circuits between lights and outlets due to arc fault and ground fault protection requirements in the current electrical code.
  • Updating the current electrical panel box to 200 amp service.
  • The electrical contractor’s specialty can be a cost factor. Commercial electrical contractors don’t often like taking residential rewiring jobs and often charge a premium to do so.
  • The electrical contractor’s schedule often can be a factor. Busy contractors often will price rewiring jobs at full price or even ballpark the price because they are already overloaded with work.

Be wary of any electrical contractor who agrees to do any major electrical work, such as rewiring a house, without pulling the proper local building permits. Also, be sure the electrical contractor you choose is licensed, insured and bonded.

If you are purchasing a home that has old, outdated, or faulty wiring and you have no other choice but to have it replaced you can consider renegotiating the cost of the home, or you can ask for the repairs to be covered by the seller before you move in.

In any way, during a home inspection, any potential hazards and issues will be covered, and you will be informed if further investigations need to be carried out.

During the purchase process, you can do a DIY home inspection prior to making a formal offer, but this should not stand in place of a professional home inspection. See our article Complete DIY Home Inspection Checklist. It comes with a printable PDF download.

How Much Time Does It Take to Change the Wiring in a House?

Replacing the whole electrical wiring system in a home is not just cost consuming but also time-consuming. Frequently this needs to be well-planned.

The time needed will vary depending on:

  • The size and age of the home.
  • Overall conditions.
  • The number of electrical circuits needed.
  • The type of already installed electrical panels and wiring.
  • The need for demolition work and overall access to the wiring.

Rewiring a single room (for example a kitchen) may take up to two days. And changing the wiring in a three-bedroom house can take anywhere from three to seven days (in empty houses). And in some cases, even more, depending on the size of the property and if any extra work needs to be done.

Replacing the wiring is very inconvenient because your home will be without electricity during that time. A lot of people may consider moving out while the work is being carried out.

Will Old Wiring Affect Home Insurance?

Older and outdated wiring may affect your insurance.

Some of the insurance companies may refuse to insure the house until the wiring is not replaced. In the cases where they may agree to insure it if it passes an electrical inspection and they may charge you a higher premium (the same thing applies to lenders).

It is advisable to speak directly with the insurance companies to find out what their official statement will be.

Frequently they may care more about the types of circuit breakers and the electrical panel that is installed in the property as opposed to the wiring itself.

Your insurance company will likely request an inspection of the major systems, in our article Buying an Old House? Common Problems, Costs, & Benefits we discuss this and other issues that arise from old houses.

Rewiring Homes Built Pre-1990

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If you own a house built pre-1990, you may be wondering if your home should be rewired.

Should you rewire a house built in the 1980s? You probably don’t need to rewire your house yet, unless you are experiencing some electrical issues such as dimming lights, tripping breakers, etc. However, you are approaching the age threshold and we would recommend having an annual electrical inspection performed by either a certified home inspector or a licensed electrician.

Should you rewire a house built in the 1970s? If your house is built in the 1970s and has all original panels and wiring, you are at a point where you would benefit from re-wiring your home. The house likely has one of the many brands of faulty panel boxes and ungrounded wiring. Having an annual electrical inspection performed by either a certified home inspector or a licensed electrician should be a top priority.

Should you rewire a house built in the 1960s? If your house is built in the 1960s and has all original electrical panels and wiring, you are within the age threshold where rewiring your home is likely needed. The house likely has one of the many brands of faulty panel boxes and ungrounded cloth sheathed wiring. We would recommend that you have an electrical inspection performed.

Should you rewire a house built in the 1950s or before? If your house is built in the 1950s or before and has all original electrical panels and wiring, you are beyond the age threshold where rewiring your home is most likely needed for both modernization and safety concerns. We would recommend having a thorough examination of the entire electrical system performed by a licensed electrician.

Buying a home with old wiring can be a deal-breaker without proper knowledge. In our article Home Inspection Deal Breakers That Can Kill The Sale of Your Home, we outline some of these pitfalls and what you can do to make your transaction a successful one.

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Hubert Miles

I've been conducting home inspections for 17 years. I'm a licensed Home Inspector, Certified Master Inspector (CMI), and FHA 203k Consultant. I started HomeInspectionInsider.com to help people better understand the home inspection process and answer questions about homeownership and home maintenance.

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