During home inspections—especially in older homes—it’s not uncommon to encounter outdated electrical wiring. Three types that frequently raise concerns are knob-and-tube wiring, BX (armored cable) wiring, and early ungrounded Romex. While many of these systems may still function, they were designed for a very different era of electrical demand and can pose safety, insurance, and resale challenges today.
Understanding these wiring types helps homeowners make informed decisions about safety, upgrades, and long-term value.
Knob-and-Tube Wiring
Knob-and-tube (K&T) wiring was commonly installed in homes from the late 1800s through the 1930s.
How it works
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Individual hot and neutral wires run separately
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Porcelain knobs secure wires to framing
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Porcelain tubes protect wires as they pass through wood
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No grounding conductor
Why it’s a concern
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No grounding: Increases the risk of shock and makes modern surge protection ineffective
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Aging insulation: The rubber insulation becomes brittle and cracks over time
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Fire risk: Exposed or deteriorated wiring can overheat
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Incompatible with modern use: Not designed for today’s appliances, electronics, or electrical loads
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Insurance issues: Many insurers refuse coverage or charge higher premiums
While knob-and-tube was considered safe when installed correctly, it is now widely regarded as obsolete and risky.
BX (Armored Cable) Wiring
BX wiring, also known as armored cable, became popular in the early to mid-20th century.
How it works
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Insulated conductors wrapped in a flexible metal sheath
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Early versions rely on the metal armor as a grounding path (not a dedicated ground wire)
Why it’s a concern
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Unreliable grounding: Over time, corrosion and loose connections can break continuity
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Deteriorating insulation: Older rubber insulation can crumble and expose live wires
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Not up to modern code: Does not meet today’s grounding and safety standards
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Harder to repair: Less flexible and more fragile than modern cable
Later versions improved grounding, but older BX wiring still commonly found in homes can present safety and performance issues.
Ungrounded Romex Wiring
Early Romex (non-metallic sheathed cable) became common in the mid-20th century. Some older installations include only hot and neutral wires, without a ground.
Why it’s a concern
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No equipment grounding: Increases shock risk
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Limited protection: Modern electronics rely on grounding for safe operation
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Code limitations: Ungrounded systems often require GFCI workarounds rather than full compliance
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Upgrade complications: Adding grounded outlets without proper wiring can create a false sense of safety
While safer than knob-and-tube, ungrounded Romex still falls short of modern electrical expectations.
Why These Systems Are Considered Hazards Today
Modern homes demand far more electricity than homes did decades ago. Outdated wiring systems were not designed to handle:
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High-wattage appliances
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Central air conditioning
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Home offices and EV chargers
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Smart home technology
Key risks include:
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Fire hazards from overheating or deteriorated insulation
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Shock hazards due to lack of grounding
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Tripped breakers or blown fuses
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Difficulty passing inspections, securing insurance, or reselling the home
The Benefits of Updating to Modern Wiring
Upgrading to modern electrical wiring offers significant advantages:
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Improved safety with proper grounding and circuit protection
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Code compliance with current electrical standards
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Insurance eligibility and potentially lower premiums
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Increased home value and buyer confidence
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Capacity for modern living, including future upgrades
Modern wiring systems are designed to safely handle today’s electrical loads while offering better protection against fire and electrical shock.
The Bottom Line
Finding knob-and-tube, BX, or ungrounded Romex wiring during a home inspection doesn’t necessarily mean a home is unsafe today—but it does signal that the electrical system is outdated and should be evaluated by a licensed electrician.
For homeowners, updating old wiring is an investment in safety, functionality, and long-term value. For buyers, understanding these systems helps set realistic expectations and informs smart decisions during the purchase process.
