You might have pondered whether it’s a good idea to look into options for getting the wiring fixed if you own an older property with knob and tube wiring or are exploring the possibility of purchasing one. Then, if you’ve started your own investigation, you can come across contradicting information about Knob and Tube, both in terms of expenses and required treatments as well as the system’s overall level of safety. How do you choose what to believe?

Nothing compares an experienced and licensed electrician’s comprehensive assessment of your unique circumstances, especially when you consider how important your peace of mind and your family’s safety are. This is crucial when wiring with knob and tube. Despite the preceding caution, this article will assist you in making a knowledgeable initial assessment of your wiring by outlining the crucial Knob and Tube concepts that everyone should be aware of as basic knowledge. If you encounter anything that is beyond your own knowledge and skills about knob and tube wirings, make sure you contact Arc Angel Electric so they can help you out with anything!

What is Knob and Tube Wiring

From roughly 1880 through the beginning of the 1940s, knob-and-tube wiring, an early, standardized style of electrical wiring in buildings, was widely used in North America. It was made up of single-insulated copper conductors that were run within wall or ceiling cavities, protected by porcelain insulating tubes that were drilled through joist and stud drill holes, and held along their length by porcelain knob insulators that were nailed into place. A flexible cloth insulating sleeve known as a loom was used to shield conductors when they entered electrical devices like lamps and switches or were dragged into walls. Cotton fabric soaked in asphalt served as the original insulation before rubber became widely used. In these installations, wire splices were either formed within metal junction boxes or were twisted together for good mechanical strength, soldered, and covered in friction tape (asphalt-soaked cloth) and rubber insulating tape.

Due to the high installation costs when compared to using power cables, which integrated both of a circuit’s power conductors in one run (and subsequently added grounding conductors), knob and tube wiring was ultimately phased out of interior wiring systems. Only a handful of very specialized circumstances defined in the National Electrical Code, such as specific industrial and agricultural settings, currently allow for new knob and tube installations in the United States.

Knob & Tube Components

Knob & Tube Components

Ceramic knobs were typically cylindrical and fastened directly to the floor joists or wall studs. Although some were made in two pieces with pass-through grooves on either side of the nail in the middle, the majority had a circular groove going around their whole circumference. To prevent breakage during installation, a leather washer was frequently used to cushion the ceramic.

The knob might be used to firmly and permanently attach the wire by wrapping electrical wires around it and fastening them with tie wires. The knobs allowed for direction changes kept cables from being under too much tension and separated the wire from a potentially combustible framework. The wires could effectively dissipate heat since they were hung in the air.

The cables were routed through ceramic tubes that were placed in holes drilled in floor joists or wall studs. By doing this, the wires were protected from contact with the wood framing members and compression when the house shifted. When wires crossed over one another, ceramic tubes were occasionally employed as protection in case the higher wire were to break and fall on the bottom circuit.

The role of the ceramic cleats, which were block-shaped components, was identical to that of the knobs. Cleats weren’t always used in knob and tube installations. When such an enclosure was employed, ceramic bushings shielded each wire entering a metal device box.

Every time a wire crossed over or under another wire, when a wire touched a metal device enclosure, and in other conditions outlined by code, a loom, a woven elastic insulating sleeve, was placed over the insulated wire to give further protection.

A connection point between the wiring system proper and the more flexible cloth-clad wiring found in light fixtures or similar permanent, hard-wired devices is often made of another ceramic component. When a generic power outlet was required, the wiring could be fed straight into the junction box using a ceramic bushing and a tube of protective loom.

Surface-mounted, suspended, or flush-mounted wiring fixtures such as light switches, receptacle outlets, and lamp sockets were commonly used in walls and ceilings. The wires and device were only ever enclosed in metal enclosures in the last instance.


K&T wire was less expensive to install than other wiring techniques in the early 1900s. For many years, K&T wiring, conduit, armored cable, and metal junction boxes were among the options available to electricians. Conduit methods were thought to be of higher quality, although they were much more expensive than K&T. Flexible armored cable was around twice as expensive as K&T in 1909, and conduit was roughly three times as expensive. Because it was less expensive for building owners to wire a structure for electricity, knob and tube wiring has endured.

Modern wiring techniques presumptively place two or more load-carrying wires relatively close to one another, like in the case of NM-2 cable. Ceramic insulators keep the K&T wires away from the structural materials when they are installed properly.

Along with the porcelain standoffs, cotton cloth and soft rubber were frequently used as insulation for K&T wiring. The porcelain standoffs will keep any bare wires safely insulated even though the real wire covering may have deteriorated over the years. With bare-wire electric fencing for cattle, porcelain standoffs are still often used today, and these standoffs can handle much larger voltage surges without running the risk of shorting to ground.

When utilized within the original current-carrying limits, which are roughly ten amps per circuit, K&T wiring that was placed correctly and hasn’t been destroyed or improperly modified since then is generally safe.


When knob-and-tube wiring was popular, the criteria for wiring installation were less stringent than they are now. The primary technical drawbacks of knob-and-tube wiring techniques when compared to contemporary electrical wiring standards are as follows:

  1. never had a conductor for safety grounding
  2. did not restrict switching to the hot conductor (the so-called Carter system connects electrical loads across a three-way switch pair’s common terminals).
  3. allowed for in-line splices to be made without a junction box in walls; however, this drawback is balanced by the durability of the soldered and taped junctions that were in use at the time.

Throughout the years, the cost of materials increased more slowly than the cost of labor for electricians. This eliminated the cost advantage of K&T systems, especially since they needed meticulous hand-wrapping of connections in layers of insulating tape as well as time-consuming skilled soldering of in-line splices and junctions.

Knob-and-tube wiring is capable of carrying a lot of current. But most household knob-and-tube setups still in use today, those from before 1940, have fewer branch circuits than is ideal these days. Even if the electrical loads at the time of installation were sufficient for these systems, modern families employ a variety and volume of electrical devices that was unanticipated at the time. After World War II, new electrical equipment and appliances became widely available, which led to a sharp increase in household energy demand.

Modern house buyers frequently discover that older K&T systems are unable to handle the levels of power consumption in use today. Homeowners who would swap out broken fuses with fuses rated for more amperage started abusing first-generation electrical systems. The circuits’ over-fusing exposes the wiring to higher current levels and increases the possibility of heat- or fire-related damage.

Building modifications may potentially harm wiring with knobs and tubes. Its rubber and cotton insulation are brittle and prone to drying out. Rodents and negligent actions, such as hanging things from cables in easily accessible places like basements, may also cause harm.

At the moment, the use of loose, blown-in, or expanding foam insulation over K&T wiring is prohibited by the National Electrical Code of the United States. This is due to the fact that K&T is made to allow heat to disperse into the surrounding air. As a result, replacing the wiring in impacted homes is frequently necessary as part of energy efficiency upgrades that involve insulating previously uninsulated walls. However, the NEC has been changed by California, Washington, Nebraska, and Oregon to conditionally permit insulation around K&T. They didn’t discover any fires that could be directly related to K&T, and they now allow insulation as long as the house first passes an electrician’s check.

Insurance companies may decline coverage as K&T wiring ages because they believe the danger is higher. Many insurance providers won’t even consider writing new homeowner’s policies unless the K&T wiring is completely changed or an electrician certifies that it is in good condition. Additionally, unless the electrical service is updated, many institutional lenders would not finance a home with the comparatively low-capacity service typical with K&T wiring. Some insurers could approve partial renovations if low-demand lighting circuits are left untouched.

What to Do If Your Home Has Knob and Tube Wiring

What to Do If Your Home Has Knob and Tube Wiring

It’s not necessary to have your home’s knob and tube system removed and replaced just because it’s there. However, it’s wise (and frequently necessary) to hire a professional to check your knob and tube system for dangers.

Rewiring a house costs between $1,500 and $10,000, depending on the difficulty of the job and the size of the new service panel, if it’s time to replace the outdated system. Always be mindful of the safety of the electrical wiring in your home, and never try to rewire it yourself.

If you want your knob and tube wiring system tested or replaced, get in touch with a local electrician like Arc Angel Electric. They will look for broken or improperly modified circuits and suggest further safety measures to lower the risk of shock and fire.

Tips for Safe Wiring of Knob and Tube

If you adhere to a few safety precautions, unmodified and unextended knob and tube wiring circuits are often safe.

Have an Inspection

It’s improbable that the inspector could see all of the wiring in the house, even though you most certainly had your home inspected when you bought it. Therefore, it’s a good idea to hire an inspector to check the circuit whenever you remodel your home or open the walls for whatever reason and discover K&T wiring. This is particularly true if you find splices or wiring changes inside the wall. Splices are locations where two or more wires are linked together.

When it comes to your home, it’s always better to be safe than sorry, even if you’re unsure whether what you’re seeing is a splice or a wiring modification. Call an expert from Arc Angel Electric if you’re unsure

Let it Be

If you don’t have the skills of an electrician, keeping knob and tube wiring mainly involves letting it alone. After this long, K&T wire casings are often fragile, and moving them can result in cracks in the covering. It can be dangerous to make any changes to this obsolete system, so leave it to the experts.

Don’t Splice

If an inspector approves and a competent electrician uses a RomexR cable, they may be able to extend a K&T circuit at a junction box. However there are certain limitations, and the job may only be done by a licensed electrician. It is never permitted to connect K&T wiring to RomexR outside of an electrical junction box.

Make It Separate from the Insulation

Turn off your power at the breaker box if you discover K&T wiring in your basement or attic that touches insulation. Then, while donning safety gear (rubber gloves, long sleeves, eye protection, and a mask), carefully remove the insulation apart from the wiring to let heat escape from the wires. After removing the insulation, take care not to get your hands on the wires, tubes, or knobs directly, and refrain from making any modifications to the wiring system.

When remodeling, remove the knob and tube wiring system

When knob and tube wiring is exposed during a renovation project, you should definitely factor in the expense of replacing it. During a remodel, K&T systems need to be replaced frequently. The best (and safest) way to deal with outmoded circuits is to remove and replace them, even if keeping the older system is permitted.

More Options for Fixing Knob and Tube Issues

The majority of us are going to concur that it is preferable to deal with Knob and Tube now rather than to deal with it eventually. We have discussed the benefits of having wiring professionally inspected. So let’s talk about the options a homeowner has for dealing with wire made of knobs and tubes that are no longer safe.

There are basically two choices. You have two options: either completely remove the existing wire and install new wiring or keep the components of the Knob and Tube system that are difficult to access in place and splice new branch circuits and wiring to them. Both strategies are permitted by the NEC, but it is quite specific about the rules for doing so. Insurance companies and local construction laws may have more exacting requirements.

In most cases, it is preferable to entirely remove Knob and Tube and rewire the entire house. If it fits into your budget, this provides the greatest piece of mind. In the event that you choose this path, a new wire will be grounded. Additionally, more branch circuits can be created to spread the demand load over numerous circuits as opposed to the original handful. At the same time, everything will be brought up to code, including the installation of specific necessary circuits, GFCI and AFCI protection across the residence, and three-pronged, tamper-resistant outlet covers. A qualified electrician from Arc Angel Electric will be able to clarify code requirements for the minimum number and location of outlets as well as other circuit requirements. Upgrades to your service and load centers can also be desirable. If you already have fuse boxes, you can swap them out for more modern breaker box load centers.

When installing new wire, electricians can frequently use existing receptacle and lamp placements. They will replace boxes when necessary and get rid of outdated wire when they can. When cutting out the old Knob and Tube conductors, qualified electricians will make every effort to eliminate any evidence of them, but they will always make sure that power cannot be accidentally reconnected to them later. Occasionally it won’t be able to fish wires through walls without making cuts, usually at the tops or bottoms and, if fire-blocking is present, above and below cross members in the center of walls. Professional patching and refinishing are required for the wall holes. In advance, discuss with your contractors who will be in charge of these repairs.

Certain circumstances can warrant leaving portions of the Knob and Tube wiring in place. Some older, well-kept properties retain their appeal because of their historical charm or fine, frequently irreplaceable finish work despite their age. For instance, an electrician working on a complete upgrade might decide, in consultation with the homeowner, to keep a three-way switching circuit in place. The circuit might not be feasible to fish with new wiring to the present switch locations without breaking into the walls because it may have been built in a spotless wall between the second floor and the main level surrounding a lovely staircase.

You might own a home that is historically significant or one that you believe needs extra attention. Asking your electrical contractors how they intend to install new wiring without causing damage to your house is acceptable.

Electricians will only draw new, grounded branch circuit wiring from the center of the load to the final few inches of each current circuit’s available Knob and Tube wiring if the decision is taken to only remove the wiring that is easily accessible. There will be new junction boxes placed, and each conductor for a knob and tube will go into the box through a separate bushed hole. Additionally, a second hole will be used to insert the new branch circuit wiring into the box, and connections will be created between the two systems. To preserve as much of the exposed insulation on cracked wiring as possible, the electricians must exercise extra caution. To do this, they might employ shrink tubing or tape rated at 600 volts. The present wire will remain ungrounded if a metal box is used since it won’t be linked to the grounding system and won’t be linked with the grounding conductor.

Frequently Asked Questions

Frequently Asked Questions

Is it safe to buy a house with knob and tube wiring?

It can be safe to purchase a home with knob and tube wiring, but it relies on a number of conditions. Although knob and tube wiring is an antiquated electrical system that might not adhere to current safety requirements, it is not inherently harmful. The wiring’s state, how well it has been maintained, and whether any improper alterations have been done throughout time all have a significant role in the safety of the home. It’s critical to have a certified electrician perform a complete assessment of such a home before making a purchase decision to determine the safety of the wiring and whether any modifications or replacements are required.

Is knob and tube wiring against code?

Knob and tube wiring frequently violates local electrical code regulations. Knob and tube wiring may not contain the protective features present in more recent wire systems, such as Romex, because modern building requirements have changed to promote safety. As a result, knob and tube wiring is frequently seen as obsolete and incompatible with modern electrical regulations. Local building rules can differ, so it’s important to speak with your local government officials or a certified electrician to find out the precise requirements in your area.

Is it expensive to replace knob and tube wiring?

Since replacing knob and tube wiring frequently necessitates completely rewiring a house’s electrical system, it can be expensive. Depending on the size of the house, the wiring’s complexity, and the quantity of other required electrical work, the price may change. Knob and tube wire replacement occasionally necessitate the opening of walls and ceilings, which raises the overall cost. However, it’s crucial to take into account the long-term advantages, such as improved safety and the capacity to accommodate contemporary electrical requirements. Replacement costs are an investment in the operation and safety of your house.

Is knob and tube better than Romex?

Romex and knob and tube wiring are two distinct electrical wiring schemes, each with benefits and drawbacks. An outdated wiring system like knob and tube wiring might not have the capacity or safety features of more recent wire like Romex. Romex, a kind of non-metallic encased cable, is frequently seen as safer and better suited for contemporary electrical requirements. It is simpler to insulate and can tolerate greater electrical demands. Nevertheless, whether one is “better” than the other depends on your particular needs, your concerns for safety, and the condition of the existing wiring in your home. Romex or any contemporary wiring system should often be upgraded for better usefulness and safety.


Due to faulty alterations and the addition of building insulation, knob-and-tube wiring is probably a safety threat. Inspectors must be cautious when using this antiquated method and be ready to warn their clients of any potential risks. When you face any issues or problems concerning knob and tube wiring in your home, make sure to call for a professional help from Arc Angel Electric!

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