Home wiring and electricity have gone through some rapid advancement over the last century. This leaves some older homes with wiring that might be potentially out of date. In some of these cases, you might be dealing with a “Century” or “Historic” home that has been preserved for posterity. In others, older wiring might just be a matter of budget concerns.

While there isn’t a lot of it around any longer, this type of open-wire system was added to homes with the first wave of residential electrical installations of the early 1900s. It was still commonplace when President Roosevelt push through the rural electrification act and lasted straight through to the early 1940s. While it was considered outdated after World War Two, many electrical safety codes still allowed it to remain as the active wiring system in homes up to the late 1970s.

If you live in an older home or you are thinking about buying a home or building with knob and tube wiring, you might be wondering if it is truly safe?

How To Identify Knob & Tube Wiring Look Like?

Older, historic homes and buildings might still have outdated knob and tube wiring. Though it’s pretty easy to identify. As the name implies it uses a series of round white knobs and tubes to run wiring through a home or building from the basement fuse box to all the rooms of the house and usually the attic.

The components look just like white, ceramic, spool-like knobs and tubes. The black electric wires then pass through the knobs, which support each individual wiring strand. The heavy ceramic tubes are there to protect wires where they run through joists and other structural components of the house.

It’s usually easier to spot knob and tube wiring components in an unfinished basement or attic. In a lot of the interior rooms, the knobs and tubes are often hidden behind in the walls or integrated into the spaces behind chunky plaster lath.

If you see evidence of knob and tube wiring in the basement or attic of an older home, you have to assume that it is the case throughout the rest of the interior walls.

Is Knob and Tube Wiring Considered Safe?

Technically knob and tube electrical wiring in your home are not illegal. Though it is still widely considered to be an obsolete wiring method. Especially when you consider that the era it was used in homes didn’t have the immense electrical demand that they do today. In the early 1900s wiring was used to do little more than run lights, a fan, and a few of the earliest electric cooking appliances.

Today most modern homes have high electric demands from air conditioners, microwaves, dishwashers, refrigerators, electric ranges, big-screen TVs, computers, and a glut of personal electronics. This level of demand simply exceeds what even the most robust knob and tube electric wiring can possibly handle. Not to mention the risk of blowing the fuses that generally connect knob and tube wiring to the current provided by the local power grid.

Knob & Tube’s Other Safety Risks

Of course, electric demand, the heat inside the walls, and the risk of blowing fuses are just the tip of the iceberg when it comes to the dangers of knob & tube wiring. An equal worry with this outdated type of wiring is the fact that there isn’t any form of electrical ground.

When you look at the outlets that connect to the knob and tube wiring, you will see just two slots, without any third area for a ground prong to be inserted. It only has a hot and a neutral wire, which places an enormous safety risk on appliances that need to be grounded to safely operate. Not only can this damage the appliance that you plug into the knob and tube outlet, but it can also increase the risk of an electric fire starting inside the walls from an overloaded wire.

Knob & Tube Wiring Gets More Dangerous With Age

When they were first made, knob and tube wires were wrapped in a special rubberized cloth that was standard in that era. As time goes by this rubberized sheath gradually starts to become brittle. As time goes on, it can crack and even start to fall off, which leaves the hot, ungrounded wires exposed to the surrounding air. This can be a major risk for shocks, short circuits, and electrical fires.

It’s especially concerning in places like bathrooms, kitchens, and laundry rooms, or anywhere that wiring passes near a wet wall where there is a risk of water leaks. Not to mention the very real risk posed by animal damage from mice and rats that often take up residence in the walls of older homes.

Heat Concerns From Modern Insulation

Most of the contemporary homes that had knob and tube wiring installed in them didn’t have any insulation in the attic. As these homes were updated, many homeowners who were tired of sky-high heating bills had modern-day insulation installed in the attic. While this helps reduce heating bills in the winter it also serves to insulate the knob and tube wiring systems in the attic, which were meant to be allowed to cool in open air. This excess thermal energy can melt the outdated rubberized coating on the wires as well as lead to a heightened risk of fire in a place that isn’t readily visible.

Can I Get Homeowner’s Insurance If I Buy A House With Knob and Tube Wiring?

The very high fire risk associated with knob and tube wiring means that most insurance companies will not approve a homeowner’s insurance policies on houses with knob and tube wiring. This also affects your ability to get financing, as most lenders require you to have an up-to-date homeowner’s insurance policy in place before the underwriters will sign off on the loan approval.

How Much Does It Cost To Replace Knob & Tube Wiring?

The cost to replace knob and tube wiring can vary depending on the size of the home as well as the type of outlets and electrical panel it already has in place. For an average two-story home could be several thousand dollars. Though the price will likely go up if the home has more than two floors or you need to also upgrade the wiring in outbuildings like a detached garage or a workshop.

The best time to replace wiring is when remodeling your house. The drywall/plaster/ paneling will need to be removed from the walls and ceilings exposing the knob and tube wiring so it can be replaced with new code compliant wiring.

If you are thinking about purchasing an older home that has knob and tube wiring, or you suspect has knob and tube wiring, you should definitely request an inspection before making an offer. The electrician who performs the inspection can then give you a ballpark number on the cost it would take to upgrade the home to modern standards and safety codes. You can then factor this information into the offer you make to the previous homeowner.