Published August 31, 2026 by National Electric NM
Older homes are part of New Mexico's character, and some still carry wiring from another era. Two types deserve attention.
Knob and tube
Used until about the 1940s, knob and tube runs single wires through ceramic tubes in framing and around ceramic knobs. It has no ground wire. The rubber and cloth insulation becomes brittle with age, and the system was designed to shed heat into open air, so covering it with attic insulation is a hazard.
Aluminum branch wiring
From about 1965 to the mid-1970s, many homes were wired with aluminum instead of copper. Aluminum expands and contracts more as it heats and cools, which loosens connections at outlets and switches and can cause overheating.
How to tell what you have
- Look in the attic or crawl space for ceramic knobs and tubes.
- Check exposed cable in the garage or attic for the marking AL or ALUMINUM.
- Note your home's age: before 1940, or roughly 1965 to 1975.
- Book an electrical inspection for a definite answer.
Your options
For knob and tube, replacement is the long-term answer, either as part of whole house rewiring or circuit by circuit. For aluminum, you can replace it with copper or have every connection repaired with connectors made for joining aluminum to copper. See knob and tube and aluminum wiring replacement.
Insurance
Many insurers ask about wiring type and may decline or surcharge homes with either system. Documentation of a professional repair or replacement often resolves it.