Introduction
Knob and tube wiring was commonly used in buildings in the early 20th century. As someone involved in managing or renovating commercial real estate today, you may encounter this old wiring method and need to evaluate whether to keep or replace it. There are arguments on both sides of this issue. In this article, I aim to provide an in-depth look at the pros and cons of keeping or removing knob and tube wiring in modern commercial spaces.
What is Knob and Tube Wiring?
Knob and tube wiring consists of insulated wires that are suspended between porcelain knobs and run through porcelain tubes. It was the standard wiring method in North America from about 1880 to the 1930s.
Some key characteristics of knob and tube wiring:
- Two separate wires, one for hot and one for neutral, rather than an insulated cable containing both
- Open air between wires rather than compact insulation
- Wires attached to porcelain knobs or run through porcelain tubes
- No ground wire
This type of wiring can still be found in older commercial buildings today.
Arguments for Keeping Knob and Tube Wiring
There are some reasonable arguments for leaving old knob and tube wiring in place, including:
It Still Functions Properly in Many Cases
- The wiring was designed to last a long time. The porcelain and wire insulation are durable.
- If the insulation is intact and wires properly supported, it can continue functioning safely for many more years.
Replacement Can Be Very Costly and Disruptive
- Rewiring an entire building with modern wiring is an extremely expensive project.
- In occupied buildings, renovations would disrupt business operations.
Waste Concerns if Serviceable Wiring is Removed
- Functional knob and tube would end up in landfills.
- New wiring uses resources to manufacture and ship.
Retains Historical Accuracy
- Original wiring helps preserve the historic character of old buildings.
- Period-appropriate look has value for some owners and occupants.
Arguments for Replacing Knob and Tube Wiring
However, there are also good reasons why knob and tube wiring often needs to be replaced in modern commercial spaces:
Fire and Shock Hazards
- No ground wire means no ground fault detection. Faults can energize metal parts of appliances.
- Open air design provides oxygen to fuel fires in the event of an arc or spark.
- Brittle insulation on old wires cracks over time.
Cannot Support Modern Power Loads and Devices
- Insufficient for today's power demands - lighting, computers, HVAC systems.
- Most smart building technology and controls are incompatible.
Against Modern Electrical Codes
- Knob and tube is prohibited by electrical codes for new construction and renovation in many jurisdictions.
- Violations could affect insurance coverage or require retroactive corrections.
Reduces Property Value
- Many buyers or tenants will view knob and tube wiring as unsafe and outdated.
- It may limit potential property sales, rents or financing.
Difficult to Insure
- Many insurance companies are reluctant to underwrite properties with knob and tube.
- Those that do often impose restrictions or higher premiums.
Key Considerations for Evaluation
When evaluating whether to keep or replace old knob and tube wiring, some key factors I consider are:
- The condition and safety of existing wiring based on inspection
- The cost and disruption of full rewiring
- Building/fire codes and requirements in my jurisdiction
- The need for increased electrical capacity
- Plans for building upgrades like smart technology
- Insurance and financing implications
I also consult with qualified electricians and engineers to get professional assessments specific to my building. They can help advise on any safety risks detected, as well as more limited repair options versus full rewiring.
There is no one-size-fits-all answer. But weighing all these factors helps me make an informed decision on maintaining or removing old knob and tube wiring.
Conclusion
Knob and tube wiring poses a challenging decision in older commercial buildings. In some cases, it may be perfectly safe and worthwhile to retain from cost and waste perspectives. But safety issues, capacity concerns and modernization plans often make replacement necessary. Careful inspection, expertise consultation and balancing rewiring costs versus risks and benefits lead to the best resolution for each unique property situation. With a thoughtful evaluation approach, I can decide if this antiquated yet durable wiring method still has a viable place in my building.