Many older homes throughout San Mateo County, Santa Clara County and the San Francisco Peninsula were originally built with knob-and-tube wiring, an electrical system installed primarily between the 1880s and 1940s. In some cases, even into the 1950s. While innovative for its time, knob-and-tube wiring is now considered outdated and potentially hazardous, especially when used in modern homes with significantly higher electrical demands.

Why Knob-and-Tube Wiring Is Dangerous
One of the biggest risks of knob-and-tube wiring is its lack of grounding. Without a ground wire, the system provides little protection against electrical shock or power surges, putting homeowners and electronics at risk.

Over time, the insulation around knob-and-tube wiring deteriorates, becoming brittle and prone to cracking. This increases the risk of exposed wires, overheating and electrical fires. In fact, aging insulation is one of the leading causes of electrical hazards in older Peninsula homes.

Not Designed for Modern Electrical Loads
Homes today rely on modern appliances, HVAC systems, EV chargers, computers and smart technology, far more than knob-and-tube systems were designed to handle. This often leads to overloaded circuits, frequent breaker trips, flickering lights or warm outlets.

In many cases, homeowners are unaware that knob-and-tube wiring is inside their homes. It is often hidden behind walls or ceilings, especially in older San Mateo or Santa Clara County homes that may have been partially renovated without a full electrical upgrade.

Insurance + Code Compliance Issues
Many insurance companies consider knob-and-tube wiring a liability and may:

• Deny coverage
• Increase premiums
• Require removal before issuing a policy

Additionally, knob-and-tube wiring does not meet current California electrical codes, which can complicate home sales or remodeling permits throughout the San Francisco Peninsula.

Why Replacement Is the Safer Option
While short-term, limited repairs may be possible, the safest long-term solution is often replacing knob-and-tube wiring with a modern electrical system. A professional electrical evaluation can determine whether a whole-home rewire or partial upgrade is needed.

Protecting Peninsula Homes
For homeowners across San Mateo County, Santa Clara County and the San Francisco Peninsula, addressing knob-and-tube wiring is a critical step toward improving safety, lowering long-term repair costs and protecting property value.

If you are purchasing a home or have questions about knob-and-tube wiring, contact us for a free home electrical consultation.

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