How To Tell If You Have Knob And Tube Outlets?


Antique tandem and parallel receptacle. circa 1910

  • Knob & Tube era outlet & Plug configeration
  • This is the electrical version of Beta vs VHS. This plug can fit both our parallel style plugs and Tandem plugs. The parallel style plugs are the type we use today. The un-grounded type like you would find on a lamp can still operate in an outlet like this. The Tandem style plug has two horizontal flat blades. They fell out of favor in the early part of this century. The tandem parallel combo outlet was still sold in store up to the 1960. This type of outlet is almost always attached to Knob and Tube wiring as a flying splice by the original electrician.

More Examples of Knob and Tube outletsKnob and Tube outlets


The combo tandem and parallel outlet is now at least 60 years old. In most cases they are over 100 years old. These types of devices are probably original to the home. The wiring behind the wall would then have to be cloth knob and tube un-grounded wiring. Knob and Tube wiring is out dated. It should be replaced.


Tadem outlet used on Knob and Tube

Now, that we know some of the history of this style of plug. The next question is what to do when you locate them in your home? Remember that electricity is the safest way to transmit power to homes.


That is why we no longer have gas lighting.  There still is a problem when your electrical system gets neglected. Not replacing old equipment can become dangerous. Plugs and switches should be replaces ever 20 to 30 years by a qualified Electrician


outdated ungrounded outlets used with knob and Tube


Steps for repair Old Outlets

  1. Check for physical damage. Are the outlet chipped cracked or broken? (Stop using immediately)
  2. Look for signs of burning or scoring. Smelling the outlet can tell you if you have a problem.(Stop using immediately)
  3. Check to see if you plugs fit in tightly. Loose plugs can cause electrical fires. (Stop using immediately)
  4. Are there any three-two prong adapters being use in the socket. (only plug in 2 prong devices like lamps)
  5. Remove any high power appliances from these plugs. (IE. Air conditioned, Vacuums, Toasters, Computers)
  6. After you make all the above safety check start to put together a plan to rewire the older knob and tube circuits.

 Original blog was posted  here.  Read more post by GEN3

About The Author

Bill earned a degree in Electrical Engineering and Architecture, then founded Generation 3 Electric in 2000. His father, an electrician, was his inspiration. These days, Bill actively manages his company and enjoys focusing on new technology and marketing.