Knob and Tube wiring
Should you consider purchasing a property with it?
If you're in the market for a home, you may come across properties that have knob and tube wiring. This type of wiring was commonly used in homes built from the 1880s to the 1940s and consists of individual wires running through ceramic tubes and secured to the structure with porcelain knobs. While knob and tube wiring is not inherently unsafe, there are some potential risks and drawbacks to consider before purchasing a home that has it.
What are the concerns?
Wasn't intended for modern electrical loads. One of the concerns with knob and tube wiring is that it may not be able to sufficiently handle the electrical needs of modern appliances, such as air conditioners and computers, because well, they hadn't been invented yet! Increased wire temperature from modern loads can accelerate the deterioration of the exterior covering on the wire, leading to exposed bare wires that create a fire hazard. In addition, because there are many more electrical appliances and devices that require electricity in a modern home, the electrical codes now require many more dedicated circuits and many more receptacles (outlets) compared to what was required when the knob and tube wiring was first installed. In any given home that still has knob and tube wiring, the desire to expand the number of circuits to keep up with the growing electrical demands of modern living often results in improper modification of the original wiring system that can lead to overloading the circuits or increased fire hazard.
Difficulty obtaining homeowners' insurance. Many insurance companies will not cover a home that has knob and tube style wiring active, and if you can find one that does, you can be sure that your premium will be higher to account for the higher fire risk.
Can't cover it with insulation. Knob and tube style wire was designed to dissipate heat using the open air surrounding the wire. The 1987 version of the National Electrical Code made it a code violation to cover knob and tube style wire with insulation, which does not allow for heat dissipation via the open-air normally surrounding the wire. Obviously, in our Fargo area climate, this can be a major issue for homeowners wanting to improve energy efficiency of a home by adding insulation. If knob and tube wiring is to remain in place, the homeowner/insulation contractor may need to find alternative ways of improving energy efficiency in order to comply with the electrical code.
No ground wire. Older wiring such as knob and tube does not have a ground wire. A ground wire is the bare copper wire found within the plastic sheathing of modern wire, along with the black wire (hot) and the white wire (neutral). The ground wire is intended to do nothing most of the time. However, when something goes wrong, it is there for safety. It provides stray electrical current a path of least resistance back to its source, instead of through you. The ground wire connects to devices via the hole on modern receptacles that looks like an open mouth. If the outlets in an older home only have two vertical slots and does not have that open mouth shaped third hole, that is telling you that the wiring in the house does not contain a ground wire.
But wait, if the ground wire is there for safety on modern homes do I need to re-wire a house that doesn't have a ground wire? And why do so many of my household appliances only have two prongs if the ground wire is so great? Great question, I'm glad you asked! You are most likely to see three-pronged plugs on devices that have internal electronics as well as appliances that have metallic housings such as a washing machine. Appliances that only have two prongs are designed to be "double-insulated" as protection from ground faults. As for whether you need to re-wire a house that has no ground wire, no, not necessarily. As stated, you can safely operate appliances that were designed to have only a two-prong plug with no ground.
But, what if I want to use a device that has a three-prong plug? Do I have to re-wire the home then? Nope, there is another code-compliant work around in that situation utilizing a GFCI/AFCI receptacle for safety. Check out the video below for more on that. One thing to note though is that using a GFCI in this scenario doesn't mean you have a grounded system. As such, your surge protector that you are using to protect your three-prong laptop, is nothing more than a glorified extension cord. This is because the surge protector is designed to use a ground wire in a surge event.
5. It's just really old. As mentioned, knob and tube was utilized from the 1880's to the 1940's. So, the newest installation will have occurred around 75 years ago! A knob and tube system that is in good shape and has not been improperly modified over the last 75-140 years can definitely still work safely, however, the problem is that it becomes less and less likely to find the wiring in good shape simply due to the age and the deterioration of the sheathing as well as improper modifications that are very likely to have occurred over that large time period.
Replacing knob and tube wiring can be a costly and time-consuming process, as it involves removing the old wiring and installing new wiring throughout the house. This can also be a messy and disruptive process, as it may require opening up walls and ceilings to access the wiring. Depending on the size of the home and the extent of the electrical system, the cost of replacing knob and tube wiring can range from a few thousand dollars to tens of thousands of dollars.
In conclusion, knob and tube wiring can present some potential risks and drawbacks, but it may still be possible to purchase a home that has it if you found your dream home and you're willing to do your due diligence. At Foresight Home Inspection, it is not our place to tell you whether or not you should purchase a property. Rather, we strive to provide you with the facts and information needed to help you make that decision on your own.
That's all, until next time!
