How to ID knob and tube wiring

Knob and tube wiring can be dangerous and should be replaced - here's some info on this dated electrical system.



Knob and tube wiring is common in the Puget Sound region as it was used heavily between 1880 and 1930 - if your property was built within that time frame it may have some knob and tube. Knob and tube wiring is outdated technology. When knob and tube was being installed in homes people didn’t have a washer and dryer, dishwasher, air conditioner, hair dryer, etc. - in other words, the electrical load wasn’t nearly as heavy. With so much demand on a dated electrical system, the wiring can overheat and create a fire hazard. It is best to install updated wiring systems.


How to ID knob and tube


Generally speaking, knob and tube is easy to spot. The best places to check for knob and tube is in your basement or in the attic - in these areas knob and tube wiring will hang freely from the ceiling. White, ceramic tubes and knobs that the wiring snakes through are trademarks of this system. Look for a rubber cloth that wraps around the wires as well - more on this below.


Knob and tube can also exist in the walls - this requires a little more digging (and drywall work). In order to properly identify knob and tube in the walls (also called spider webbing) we recommend bringing in an electrician to diagnose.


What makes knob and tube wiring dangerous?


First of all, there is no electrical ground with knob and tube wiring - there’s just a hot and neutral wire. Running large appliances without a grounding wire is dangerous because of the amount of energy required to power these systems. Another safety concern with knob and tube is that it doesn’t age particularly well. As we mentioned above, knob and tube is wrapped with a rubber cloth that can deteriorate over time (especially after 90 - 140 years). This deterioration can present exposed electrical wiring that can be a fire and electrocution hazard.


Insulation and water damage can create a larger issue when your knob and tube cloth protection has worn down. Exposure to newly installed insulation can be a major fire hazard and unnoticed water leaks do not mix well with unprotected wiring.


Insurance and home value issues


Obtaining or renewing insurance on a property with knob and tube can be difficult. Insurance companies don’t want to cover properties with knob and tube because of the additional liability. At the least you’ll have to pay extra for proper coverage.


On top of that, the demand for a house with knob and tube wiring will go down. Again, there are many properties in the Puget Sound region with knob and tube so it’s not uncommon. But as more and more homes are upgraded and new homes come on the market, knob and tube will become a bigger concern for potential home buyers. This will translate to lower prices for sellers of knob and tube properties.


Here at HomeRiff, we’ve worked with knob and tube extensively in our customers’ properties. Let us know how we can help!