Okay, let's break down the situation with knob and tube (K&T) wiring and your customer's request. This is a common scenario, and it's essential to handle it safely and according to code.

Key Concerns and Considerations


Safety First

K&T wiring is an old system with inherent safety risks. It lacks a grounding conductor, insulation can degrade over time, and it's often overloaded by modern electrical demands. Replacing as much as possible is a good starting point.2.

Code Compliance

Modern electrical codes (like the NEC in the US) have specific requirements for electrical work. Simply splicing K&T to Romex without understanding the system and addressing the grounding and overcurrent protection issues will likely violate code and create a hazard.3.

Grounding

The most significant issue is the lack of a grounding conductor in K&T. Romex (NM cable) requires a ground.4.

Overcurrent Protection (Fuses)

The fact that you see fuses on both the neutral and the hot conductors in a K&T system raises red flags. This isn't standard practice and is a sign of potential problems or someone attempting to resolve an imbalance.5.

Overcurrent Protection Mismatch

You mentioned 15A fuses on the neutral and 20A fuses on the hot. This is definitely wrong. The neutral conductor should NEVER be fused or protected with a breaker higher than the hot. In most residential applications, the hot and neutral conductors should be the same size.

Answering Your Questions



"Can I splice K&T wires with Romex in the basement inside an electrical metal box?" Technically, Yes, you can make the connection in a box. The NEC does permit extensions from existing wiring if specific conditions are met. HOWEVER... Practically, this is Highly Problematic and often not the right solution for several reasons: Grounding

Connecting Romex to K&T will still leave you with an ungrounded circuit unless you can run a separate grounding conductor back to the main panel's grounding system (which might be possible, but tricky and depends on the panel's age and setup).

Code Violation Potential

Depending on your local codes and AHJ (Authority Having Jurisdiction), simply splicing K&T to Romex might be considered a modification of the existing K&T system, which would then require the entire circuit to be brought up to current code (i.e., fully replaced).

Mixed Systems

Mixing old and new wiring introduces complexities and potential for future problems. It's generally better to replace the entire circuit.

The bigger question to ask is will it pass inspection with the AHJ "I noticed there are multiple boxes in the basement with fuses protecting neutral 15A and hot 20A. Do neutral has to be protected with refuse in K&T wiring?" No, the neutral should NOT be fused. This is incorrect and dangerous. It indicates a fundamental problem with the original wiring or an incorrect modification. The neutral is intended to be a grounded conductor (at the service entrance). Fusing it can interrupt the return path and cause voltage imbalances and potential shock hazards. The overcurrent protection (fuse or breaker) must be on the hot (ungrounded) conductor only. "Because if I use Romex on home run protection will be only on hot wire." Correct. Romex, when installed correctly, will have overcurrent protection only on the hot (ungrounded) conductor. This is the proper and safe configuration. However, as mentioned above, you can't simply connect a Romex homerun to an existing K&T circuit without addressing the grounding issue.

Recommended Actions (and Disclaimer: This is for informational purposes only and does not constitute professional electrical advice. Consult with a licensed electrician)


Consult a Licensed Electrician

This is the most important step. A qualified electrician can assess the entire K&T system, identify the source of the fused neutral, and determine the safest and code-compliant solution.2.

Full Circuit Replacement (Ideal)

The best solution is usually to completely replace the K&T circuit with new Romex from the panel to the outlets/fixtures. This provides a grounded system with proper overcurrent protection and eliminates the risks associated with the old wiring.3.

Grounding Options (if partial replacement is considered)



Run a Separate Ground Wire

If replacing the entire circuit isn't immediately feasible, and your local codes allow it, you might be able to run a separate grounding conductor from the metal box where you're making the splice back to the main electrical panel's grounding bus. This is a tricky solution and requires careful attention to ensure proper grounding.



GFCI Protection

Installing a GFCI (Ground Fault Circuit Interrupter) outlet as the first outlet on the circuit can provide some level of shock protection. GFCI protection is not a substitute for a proper ground, but it can significantly reduce the risk of electrocution. However, GFCI protection may be required when extending or modifying an ungrounded circuit per NEC.

AFCI Protection

In many jurisdictions, AFCI (Arc Fault Circuit Interrupter) breakers are required on new circuits. While they don't solve the grounding issue, they can help detect and prevent electrical fires caused by arcing faults in the wiring.4.

Remove the Neutral Fuse

The fused neutral must be removed. It's a safety hazard. Identify why it was installed, and correct the underlying problem.5.

Correct Overcurrent Protection

Make sure the overcurrent protection (fuse or breaker) is sized appropriately for the wire gauge of the new Romex.6.

Inspect and Document

Carefully inspect all remaining K&T wiring for signs of damage, cracking, or deterioration. Document the location of all K&T wiring for future reference.

Important Considerations for Estimating the Job



Access

How easy is it to run new wiring? Are there finished walls or ceilings that need to be opened up?

Permits and Inspections

Factor in the cost of electrical permits and inspections.

Panel Capacity

Is the electrical panel large enough to handle the new circuits? Does it need to be upgraded?

Asbestos: In older homes, be aware of the possibility of asbestos in the insulation around the K&T wiring. If suspected, have it professionally tested and abated.In summary, while splicing K&T to Romex is possible in certain circumstances, it's often not the best or safest solution. A full circuit replacement is generally the preferred approach. Always consult with a qualified electrician to ensure the work is done safely, correctly, and in compliance with local codes. The fused neutral is a significant red flag that needs immediate attention. Flag for review