Understanding Knob and Tube Wiring

Oct 13, 2025 by leolavanderia.com.br 144 views

Introduction

As an electrician, you may have encountered homes with knob and tube wiring, a type of electrical system that was once common but is now considered outdated and potentially hazardous. When working on a project, such as the one described, where the homeowner wants to redo the 1st floor apartment, it's essential to understand the 2017 National Electric Code (NEC) requirements for knob and tube replacement. In this article, we'll delve into the NEC code and explore what it says about knob and tube replacement.

Understanding Knob and Tube Wiring

Before we dive into the NEC code, let's briefly discuss what knob and tube wiring is. Knob and tube wiring is a type of electrical system that was widely used in the early 20th century. It consists of two main components: knobs and tubes. Knobs are ceramic or porcelain insulators that are used to support the wires, while tubes are metal or porcelain tubes that are used to protect the wires from moisture and other environmental factors.

2017 NEC Code Requirements

The 2017 NEC code provides specific requirements for knob and tube wiring. According to Article 220, Section 220.14, knob and tube wiring is considered obsolete and is not permitted for new installations. However, for existing installations, the code provides some flexibility.

Section 220.14 - Obsolete Wiring

Section 220.14 of the 2017 NEC code states that "obsolete wiring" is defined as "wiring that is no longer in compliance with the requirements of this Code." This includes knob and tube wiring, which is no longer considered safe or compliant with modern electrical standards.

Section 220.14(A) - Permitted Repairs

However, Section 220.14(A) of the code allows for repairs to be made to existing knob and tube wiring, provided that the repairs do not involve the replacement of the entire system. This means that if you're working on a project where the homeowner wants to redo the 1st floor apartment, you may be able to make repairs to the existing knob and tube wiring, but you cannot replace the entire system.

Section 220.14(B) - Replacement of Obsolete Wiring

Section 220.14(B) of the code provides specific requirements for the replacement of obsolete wiring, including knob and tube wiring. According to this section, the replacement wiring must be installed in accordance with the requirements of the code, including the use of modern materials and techniques.

Section 220.14(B)(1) - Permitted Replacement

Section 220.14(B)(1) of the code states that "replacement of obsolete wiring shall be permitted where the replacement wiring is installed in accordance with the requirements of this Code." This means that if you're working on a project where the homeowner wants to redo the 1st floor apartment, you may be able to replace the existing knob and tube wiring with modern wiring, provided that you follow the requirements of the code.

Section 220.14(B)(2) - Requirements for Replacement

Section 220.14(B)(2) of the code provides specific requirements for the replacement of obsolete wiring, including knob and tube wiring. According to this section, the replacement wiring must be installed in accordance with the requirements of the code, including the use of modern materials and techniques.

Section 220.14(B)(2)(a) - Use of Modern Materials

Section 220.14(B)(2)(a) of the code states that "replacement wiring shall be installed using modern materials and techniques." This means that you must use modern materials and techniques when replacing the existing knob and tube wiring, such as copper or aluminum wiring, and modern connectors and fittings.

Section 220.14(B)(2)(b) - Compliance with Code Requirements

Section 220.14(B)(2)(b) of the code states that "replacement wiring shall be installed in accordance with the requirements of this Code." This means that you must follow the requirements of the code when replacing the existing knob and tube wiring, including the use of modern materials and techniques, and the installation of the wiring in accordance with the code requirements.

Conclusion

In conclusion, the 2017 NEC code provides specific requirements for knob and tube replacement. According to the code, knob and tube wiring is considered obsolete and is not permitted for new installations. However, for existing installations, the code provides some flexibility, allowing for repairs to be made to existing knob and tube wiring, and permitting the replacement of obsolete wiring with modern wiring, provided that the replacement wiring is installed in accordance with the requirements of the code.

Recommendations

Based on the 2017 NEC code requirements, we recommend that you:

Repair existing knob and tube wiring whenever possible, rather than replacing the entire system.
Replace obsolete wiring with modern wiring, provided that the replacement wiring is installed in accordance with the requirements of the code.
Use modern materials and techniques when replacing existing knob and tube wiring.
Follow the requirements of the code when replacing existing knob and tube wiring.

Introduction

In our previous article, we discussed the 2017 National Electric Code (NEC) requirements for knob and tube replacement. In this article, we'll answer some frequently asked questions about knob and tube replacement according to the 2017 NEC code.

Q: What is knob and tube wiring?

A: Knob and tube wiring is a type of electrical system that was widely used in the early 20th century. It consists of two main components: knobs and tubes. Knobs are ceramic or porcelain insulators that are used to support the wires, while tubes are metal or porcelain tubes that are used to protect the wires from moisture and other environmental factors.

Q: Is knob and tube wiring still permitted in new installations?

A: No, according to the 2017 NEC code, knob and tube wiring is considered obsolete and is not permitted for new installations. However, for existing installations, the code provides some flexibility.

Q: Can I repair existing knob and tube wiring?

A: Yes, according to Section 220.14(A) of the 2017 NEC code, repairs can be made to existing knob and tube wiring, provided that the repairs do not involve the replacement of the entire system.

Q: Can I replace obsolete wiring with modern wiring?

A: Yes, according to Section 220.14(B) of the 2017 NEC code, replacement of obsolete wiring is permitted, provided that the replacement wiring is installed in accordance with the requirements of the code.

Q: What are the requirements for replacing obsolete wiring?

A: According to Section 220.14(B)(2) of the 2017 NEC code, the replacement wiring must be installed using modern materials and techniques, and must comply with the requirements of the code.

Q: What are the requirements for modern materials and techniques?

A: According to Section 220.14(B)(2)(a) of the 2017 NEC code, modern materials and techniques include the use of copper or aluminum wiring, and modern connectors and fittings.

Q: Do I need to follow the requirements of the code when replacing obsolete wiring?

A: Yes, according to Section 220.14(B)(2)(b) of the 2017 NEC code, replacement wiring must be installed in accordance with the requirements of the code.

Q: What are the consequences of not following the requirements of the code?

A: Failure to follow the requirements of the code can result in electrical shock, fire, or other hazards. Additionally, non-compliance with the code can result in fines, penalties, or other consequences.

Q: Can I use knob and tube wiring in a new installation if it's been modified to meet modern safety standards?

A: No, according to the 2017 NEC code, knob and tube wiring is considered obsolete and is not permitted for new installations, regardless of whether it's been modified to meet modern safety standards.

Q: Can I use knob and tube wiring in a new installation if it's been certified by a third-party testing organization?

A: No, according to the 2017 NEC code, knob and tube wiring is considered obsolete and is not permitted for new installations, regardless of whether it's been certified by a third-party testing organization.

Conclusion

In conclusion, the 2017 NEC code provides specific requirements for knob and tube replacement. By understanding these requirements, you can ensure that your project is completed in accordance with the code and that the electrical system is safe and compliant with modern electrical standards.

Recommendations

Based on the 2017 NEC code requirements, we recommend that you:

Repair existing knob and tube wiring whenever possible, rather than replacing the entire system.
Replace obsolete wiring with modern wiring, provided that the replacement wiring is installed in accordance with the requirements of the code.
Use modern materials and techniques when replacing existing knob and tube wiring.
Follow the requirements of the code when replacing existing knob and tube wiring.

By following these recommendations, you can ensure that your project is completed in accordance with the 2017 NEC code requirements, and that the electrical system is safe and compliant with modern electrical standards.