Electrical Wiring Types: What’s in Your Walls?

What Types of Electrical Wiring Are Found in Homes?

Most homes have one of three wiring systems: knob-and-tube (pre-1940s), aluminum branch circuits (1965 to 1973), or modern copper Romex (post-1970s). Which one is in your walls determines the safety assessment, the insurance implications, and the upgrade options for your home electrical system.

Knob-and-Tube Wiring (Pre-1940s)

Knob-and-tube wiring uses individual insulated copper conductors supported by ceramic knobs and run through ceramic tube insulators where they pass through framing. It has no ground wire, cannot support modern electrical loads safely, and must not be covered with insulation (which traps heat around the conductors). Homes with knob-and-tube wiring are difficult to insure a many insurers decline coverage or charge high premiums for unmodified knob-and-tube systems. Replacement is the recommended path for any home that still has knob-and-tube as the primary wiring system. (For more on this, see How Much Does Electrical Wiring Cost?.)

Aluminum Branch Circuit Wiring (1965 to 1973)

During a period of copper shortage, residential wiring was installed with aluminum conductors for branch circuits (outlets and switches). Aluminum expands and contracts differently than the copper terminals it connects to, causing connection loosening and arcing over time. The CPSC classifies homes with aluminum branch circuit wiring as having a significantly elevated fire risk. Remediation options: AlumiConn connectors at every connection point ($1,500 to $4,000), or full copper re-wiring ($8,000 to $20,000, because the aluminum has to come out rather than be abandoned in the walls). Service entry conductors are still aluminum a this is standard and not a concern. The Electrical Safety Foundation covers where GFCI and AFCI protection is required and which jobs need a licensed electrician.

Modern Romex (NM Cable) Wiring (Post-1970s)

Non-metallic sheathed cable (trade name Romex) wraps multiple conductors a black (hot), white (neutral), and bare copper (ground) a in a single plastic sheath. This is the standard residential wiring method since the 1970s and is safe, well-understood, and easily extended or repaired. A home with modern Romex and an appropriately sized panel has the electrical foundation needed for modern loads. (For more on this, see What Affects the Cost of Electrical Wiring?.)

Conduit Wiring

Some homes and most commercial buildings use metal (EMT) or plastic (PVC) conduit with individual conductors pulled through it. This is the highest-quality residential wiring installation a wires can be replaced without opening walls, provides mechanical protection, and is the standard in garages, basements, and exterior locations even in otherwise Romex-wired homes.

Working With a Contractor on This Project

Getting the right outcome on any home services project starts before the work begins. A few consistent practices make the difference between a smooth project and a frustrating one. (For more on this, see How to Budget for a Home Electrical Wiring Project.)

Get at least two or three quotes. A single quote gives you no basis for comparison. Two or three quotes reveal the market rate for the work, expose scope differences between bidders, and let you assess contractor communication quality before any commitment is made. The lowest bid is not automatically the best value if the scope is thin or the materials are underspecified.

Ask for licenses and insurance before work starts. Verify current general liability insurance and, for any work involving workers on your property, workers compensation coverage. Licensing requirements vary by state and trade; confirm the specific requirements in your jurisdiction. A licensed contractor who carries appropriate insurance protects both parties if something goes wrong during the project.

Get the scope in writing. A written proposal that specifies materials, labor scope, timeline, what is included (permits, cleanup, disposal), and warranty terms is the foundation of a professional engagement. Verbal agreements on any of these points invite misunderstanding. For any project over $500, written scope is non-negotiable.

Clarify the payment schedule upfront. A reasonable payment schedule ties major payments to project milestones: a deposit at signing, a payment at material delivery or project start, and a final payment at completion after a walkthrough confirms satisfaction. A contractor who requires full payment upfront before work begins is a red flag in any trade.

Making a Confident Decision

The information in this article is designed to help you ask better questions of the professionals you work with, evaluate their answers with more confidence, and understand the decisions involved in this type of home services project. It is not a substitute for professional assessment of your specific home.

Every home is different. Roof slopes, local weather, tree exposure, soil conditions, and existing system condition all affect what the right solution is for your specific situation. The general principles here apply broadly, but a professional who assesses your home in person will give you guidance that accounts for the details that general articles cannot.

When you are ready to move forward, getting at least two or three quotes from licensed, insured, local contractors is the most important practical step. It lets you compare approaches, assess contractor quality, and confirm that the solution proposed matches your specific situation and budget.