Knob and Tube wiring, also known as open wiring is probably the scariest thing most home owners fear in their home. Most home insurance companies will not even insure a home if there is Knob and Tube wiring and commonly ask for either a complete re-wire or an assessment on the condition of the existing wiring from a professional electrical contractor.
There is some great information and history of Knob and Tube in our blog about Old Wiring and How It Affects Your Home Insurancewhich goes into a more in-depth look at the system itself. Knob and Tube is typically found in the oldest of houses all the way up to homes built in the 1950’s. You can identify Knob and Tube wiring as it is single individual conductors that run along joists attached by white ceramic knobs and through joists through white ceramic tubes. The hot and neutral wires were run roughly a foot apart or in separate joist cavities and all the connections were done by soldering the branch circuit onto the main trunk wires run throughout the home.
The strange thing about knob and tube wiring is that it actually is a very safe and robust electrical system for the era it was designed and installed for. Now before you jump to conclusions and think I am saying Knob and Tube is safe, we need to look closely at that statement, specifically where I say designed for the era it was installed for. Today’s homes simply have far too much electrical demand on the system that Knob and Tube was not designed to handle. This is why when looking at statistics on electrical fires, the percentage of fires in homes with Knob and Tube has increased over the years as our demands increase.
So, what are your options if you have knob and tube in your home? There are two industry accepted upgrades when it comes to knob and tube.
The first is fairly simple to understand, a complete re-wire of the home starting from the electrical panel. A complete re-wire is the safest way to ensure there is no risk of knob and tube as it is no longer being used. The issue we run into doing complete home re-wires is that it is very messy and time-consuming process, it requires extensive drywall damage and repairs and most homeowners cannot or do not want to live in the home while undertaking this task. Complete re-wires are most commonly done on older homes when they are either first purchased or an extensive renovation is going to take place.
The second option when it comes to upgrading Knob and Tube wiring is a little more complicated to understand, but the process is much quicker and cost effective. It also does not involve removing all the drywall in the home and the sheer mess that goes along with a complete re-wire.
The first step is to test all the circuitry in the home for loose connections. There a couple methods to test for this, but the easiest way is to measure voltage on a circuit with no load and then under full load. By monitoring how the voltage reacts with the change in load, we are able to look for troublesome circuits and loose connections which are buried in the wall.
The next step is to test the insulation of the knob and tube wiring. One method is to physically check the condition of the wire either in the attic or in the basement where it is visible. If it is malleable and not cracking and fracturing then it is still in decent condition. If it starts falling apart in your hands, then the knob and tube is no longer safe and needs to be removed. The second method of testing insulation of the wiring is to use a device called a Meggar, which runs a high voltage through the wire and measures the condition of the insulation. This type of test is very useful when testing newer cables, but with the age and uncertainty of knob and tube wiring, it is not always the best option.
The final stage of the upgrade can take place once all the preliminary testing has been completed and you are confident the existing wiring is still usable. This is to install GFCI protection on the circuits in the home. GFCI or Ground Fault Circuit Interrupter’s measure the current being used on a circuit as well as the return current. If it senses the slightest leak of current out of the circuit it will shut off power. GFCI’s are the receptacles with the test and reset in the middle that are commonly seen in outdoor spaces or in washrooms because of their proximity to water.
Homes with knob and Tube are not properly grounded and bonded to today’s standards and the risk of shock is much higher when using a two-prong outlet. By upgrading all the receptacles to GFCI type, this at least ensures any leaked current does not end up going through your heart.
In our opinion, we recommend going for a full re-wire as there really is no way of knowing what is hiding behind the walls. We are able to run certain tests to check voltage drop and use thermal imaging to try and find potential hot spots, but nothing can 100% guarantee like a complete re-wire.
