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Winnipeg

Knob and Tube Wiring

Older houses often have what is called ‘knob and tube’ wiring. This wiring is considered dangerous by most insurance companies today, making it hard to insure homes and buildings that incorporate it. But why is it so dangerous that nobody wants to insure it? Is it something we should fear ourselves if our homes already have this type of wiring?

Top 5 Dangers of Knob and Tube Wiring

Do you live in a home or commercial building that was built in the 1900’s to the early 1950’s? If so, then your building is almost sure to have what is called “knob and tube” wiring or an ungrounded system. Knob and tube wiring was considered “state-of-the-art” back then, but now it is very dangerous, is in violation of current legal electrical codes and is not insured by most insurance companies.

What’s so dangerous about knob and tube wiring? Let’s find out. Here are the top 5 dangers of knob and tube wiring.

1) Knob and tube wiring is two-stranded – with a hot wire and a neutral wire only – it uses no ground wire. There is absolutely no protection whatsoever when a fault occurs. Shocks and fires can easily result from faults caused by knob and tube wiring.

2) Knob and tube wiring uses sheathing for insulation and both of these disintegrate easily over time. Since buildings that contain this type of wiring are old, the problem is increased. Modern wiring uses much better insulation materials that are much safer.

3) Older electrical systems use a 60 amp service but the wire is fused with 15 amps. This means that more current is flowing through the wire than it is meant to handle, leading to excessive heat and possible fire.

4) Older electrical systems didn’t carry high ampacity loads and these extra loads cause the insulation to become brittle, exposing bare wire and the capacity to overheat which can cause fires.

5) Older systems that use knob and tube wiring also use two-prong receptacles, restricting the use of small kitchen appliances. Since there is no ground wire, there is increased chance of shock and injury, especially around areas where water is prevalent. Kitchens and bathrooms are especially at risk.

If you have an older home or commercial building (built before 1950), it’s very likely that you have knob and tube wiring installed. This poses a risk to you and your family or employees as well as your property. Most insurance companies do not insure buildings that contain this type of wiring. There are ways to fix this without rewiring your entire building which would be very expensive.

Because of the dangers involved, we urge you to contact a licensed electrician to detect and correct all knob and tube wiring in your home or commercial business. If you are selling your home or business building, it’s expedient for you to have this issue fixed in advance because your buyer won’t be able to get insurance with knob and tube wiring in place. It’s best to get it fixed before you lose a potential sale.

Knob and tube wiring used to be a state-of-the-art technology, but it’s been found to be dangerous and should be fixed or replaced as soon as possible. 

How Do I Know if I Have Knob and Tube Wiring?

If your home was built in the late 1800’s to early 1900’s there’s a good chance you do have this type of electrical wiring since it was considered state-of-the-art back then. Most houses built during that time period do indeed have knob and tube wiring that should be replaced. 

Inspect the visible parts of your home to see if you can find any knob and tube wiring. You won’t be able to look through the walls to see if any of this type of wiring is hidden underneath, but tube wiring is more predominant in the basement or the attic. Go up the stairs into your attic and follow the exposed wiring. You may have to clear out some insulation to do this as insulation often covers up wiring in the attic. Be careful not to step on any hidden wires as this can cause damage to them.

If you see wiring that is connected to little pieces of ceramic, then you do have knob and tube wiring. Remember that this type of wiring uses two wires instead of three. These two are the hot wire and the return neutral wire; the ground wire is missing. Then go down into your basement and look for the same thing. In the basement, the wiring is often below the floorboards above. Since basements don’t often have a ceiling, you’ll be able to see the floorboards by simply looking up. If you see any ceramic connectors, you have knob and tube wiring.

The attic and basement are not the only places knob and tube wiring can appear. Electrical wiring is hidden in the walls and ceilings of most houses and buildings, and you won’t be able to detect what type of wiring is hidden from view. In these cases, you’ll have to access the electrical box that houses your circuit breakers. We don’t advise you do this yourself because there are live wires within that box that, if touched, will send a straight jolt of electricity through you which could be fatal. If you do open your circuit box, be careful not to touch anything while the main power switch is on. Even if the main power switch is off, there are still live wires where the electricity enters the box. Never touch those wires unless the electric company itself has turned off all power to your home.

If you do decide to access your circuit box, look for wires coming in that only have two strands. There is a good chance that these wires use knob and tube wiring and have to be replaced. Our advice is to have to have a professional electrician inspect your home to make sure you don’t have any hidden two-strand wiring that is knob and tube. At the same time, the electrician will be able to give you a solid quote for replacing those dangerous circuits with new, modern circuits.

How Much Does it Cost to Replace Knob and Tube Wiring?

Call a qualified electrician to get an exact price on a complete home rewire. The charges include everything from running new circuits to replacing fuses with modern circuit breakers. It can be costly, but what price can be put on safety and peace of mind? You’ll rest much better knowing your wiring meets modern electrical codes for safety and performance.

A good contractor will patch the holes and the biggest hole you should see is the size of a hardball. The house should be as clean as when they started and is very none intrusive to the existing structure.

Plan to be ‘off the grid’ for a few hours while the work is being done. Electricians will need full access to your home or building and will have to shut off the power while they work. They may be able to confine this to only the circuits that have knob and tube wiring, but it depends on how that existing wiring has been done and whether additional circuits are needed or not. A good electrician will always brief you about these things so you know well in advance and can plan accordingly.

If you are purchasing a home or building that has knob and tube wiring in place, try to make it a condition of the contract that this wiring be replaced within 30 days of the sale. You may also negotiate a reduction in the price if replacing it will be up to you. Most insurance companies will agree to a contract as long as a firm agreement is in place to replace knob and tube wiring. If you are replacing knob and tube wiring, a licensed, insured electrician to do the work. 

Is Insurance Available for Knob and Tube Wiring?

Most insurance companies refuse to cover homes with knob and tube wiring in place because it does not have a ground wire. If you can’t get insurance, you can’t get a mortgage, so it’s a good idea to find out if a house or building has any knob and tube wiring before making a purchase option.

One thing that can be done to increase the safety of knob and tube wiring is to add a ground fault circuit breaker to any circuit that has this tube type of wiring on it. This type of circuit breaker adds a ground loop right at the circuit box. It was designed exactly for this type of two-wire circuit.

If you can’t get insurance on a home or building that has knob and tube wiring, your best bet is to replace the wiring. It will increase your safety and give you better peace of mind. If you are making an offer on a home or building that is affected, it’s in the interest of the selling party to have this wire replaced immediately so as not to hinder the sale of the property. If people can’t get insurance for the property, the sale won’t go through.

Getting insurance for it can be difficult and the cost will likely be more. If the knob and tube wiring is active, most insurance companies will require that it be removed prior to closing or 30 days after closing.


If the system is inactive, an insurance company might agree to write a policy. The company may either require that the wiring be removed first or in some cases will allow from 30 to 60 days after policy inception to have it professionally removed.

When buying a home with knob and tube wiring you should have a licensed electrician look the system over to determine the overall condition of the wiring. Any circuits that has been modified, damaged, or covered with insulation should be replaced. A quick-fix would be to replace the normal circuit breaker with a ground fault circuit breaker, but your insurance company may not approve of that. Replacing any circuits that is using knob and tube wiring is recommended.

How to Replace Knob and Tube Wiring

An expert should inspect the condition of the wires, connections, devices like receptacles, switches, and overcurrent protection by fuses or circuit breakers.

Be very careful replacing knob and tube wiring! This is not a job for the novice home-electrician. As with any electrical wiring, always turn the circuit off before working with anything on it. If you have to do anything with live wires (NOT recommended at all), always have a wooden or non-conducive pole you can use to push yourself away in the event you are subjected to a shock. Also use only one hand when touching electric wires because if you use two and you do get shocked, the shock will go right through your chest and a heart attack is very likely.

When the knob and tube circuit wires pass through building framing lumber a ceramic tube is used to insulate the wire from the wood. Ceramic tubes are used when tube wiring is stretched over framing lumber as well. If the ceramic tubes are cracked, additional electrical hazard is possible so be sure to make a thorough inspection.

Ground fault protection (GFCI circuit protection and possibly arc fault protection) can be added on two-wire un-grounded electrical circuits to reduce the chances of electrical shock or fire. You can do this by replacing the existing circuit breaker with a GFCI circuit breaker. They cost a bit more, but they solve the problem of not having a ground wire in two-wire situations like where tube wiring is used.

To find knob and tube wiring, make visual inspection of the entire building to identify where knob and tube wiring is visible. Then trace those circuits as far as you can into individual rooms. Use instruments (such as the Tic Tracer that senses electrical wires in walls) to trace down wiring paths in walls, ceilings, floors.

When you find knob and tube wiring, you have two choices. The first choice is the most often used, and that is to simply leave the wiring in place and run a new circuit. It’s used the most often because it’s easiest, and the remaining wiring is harmless since it won’t be reconnect it to the power source.

The second choice is to pull out that old wiring and replace it with new wiring. This takes longer and can be harder, especially if there are ceramic insulators embedded in wood. It’s better to just leave them as is and run a new circuit.

Knob and tube wiring can be dangerous and should always be replaced. We recommend not doing this yourself, but to have a licensed electrical contractor do it for you. 

Most electrical contractors recommend replacing knob and tube wiring with modern wiring. Even though there are costs involved, having the peace of mind, knowing your electrical system meets the modern electrical code for safety, goes a long way. Consult your local electrician to find out if you have knob and tube wiring and to get a quote on the cost to replace it. In the long run, you’ll be glad you did.