What Is Knob and Tube?
Knob and Tube is an older electrical wiring system that carries power through separate insulated wires. Porcelain knobs support the wires, and porcelain tubes protect them where they pass through wood. You may find this wiring in an older home's walls, attic, or floor spaces.
Quick Facts About Knob and Tube
- Category
- Older home wiring system
- Used for
- Supplying household circuits
- Common confusion
- Visible wiring versus active wiring
- Also called
- Knob-and-Tube Wiring, Knob and tube wiring
- Often discussed with
- Whole House Rewiring, Electrical Safety Inspection
Key Takeaways About Knob and Tube
- The wires usually run apart, not inside a shared cable.
- Existing wiring may serve only part of your home.
- An old-looking wire isn't proof that a circuit is active.
How Knob and Tube Works
Knob and Tube carries current from the electrical panel to outlets and lights. The hot wire carries power to a device. The neutral wire provides a return path for current. Related service: Whole House Rewiring.
Related glossary terms: Branch Circuit, Neutral Wire, Electrical Grounding.
The wires travel separately through open spaces in the home's framing. A connection may join a wire to another part of the circuit. These connections can be hidden inside walls or ceilings.
Knob and Tube wiring often lacks a separate grounding wire. A grounding wire provides a path for fault current and connects to grounded parts of electrical equipment. Modern wiring cables generally contain a grounding wire alongside the circuit wires.
A home can have both Knob and Tube and newer wiring. The visible wiring in an attic may not show the full path of a circuit. Some sections may remain in place after other parts have been replaced.
From the Earth Electric team
When we plan whole house rewiring, we trace the existing circuits and look for connections between old and newer wiring. That helps us plan where replacement wiring needs to reach. We also consider access to spaces behind walls and ceilings.
Knob and Tube in Practice: A Real-World Example
A Miami homeowner wants whole house rewiring and has Knob and Tube wiring visible in the attic. The rewiring plan accounts for the attic circuit and its connections to rooms below.
Related Services
Related Terms
Branch Circuit
A branch circuit is an electrical circuit that runs from the final circuit breaker or fuse to the outlets or equipment it supplies.
Neutral Wire
A neutral wire is a circuit conductor that carries current back toward the electrical supply during normal operation.
Electrical Grounding
Electrical Grounding is a connection between an electrical system and the earth.
Open Ground
An open ground is a break or absence in the protective grounding path at an electrical outlet.
Earth Electric
Have Questions About Knob and Tube?
Contact Earth Electric for practical guidance on Knob and Tube and related 24 hour electrician work in Miami.