As an electrician, staying up-to-date on the latest wiring methods and electrical codes is crucial. However, having knowledge of obsolete and forgotten wiring methods can also give you a competitive edge. When servicing older homes and buildings, you may encounter antiquated systems that most electricians today have never seen. Understanding these arcane methods shows your expertise and allows you to make repairs that other electricians can't. In this guide, I'll provide an in-depth look at some of the most important obsolete and forgotten electrical wiring methods that all electricians should know. Mastering these old techniques will help you stand out from the crowd.

Knob and Tube Wiring

Knob and tube (K&T) was the standard residential electrical wiring method in North America from about 1880 to the 1930s. This system uses insulated copper conductors run through ceramic knobs mounted to framing members, with tubes protecting wires through open spaces.

Here are some key facts about knob and tube wiring:

When working on older homes, I always inspect for K&T wiring. Thorough testing with a multimeter and megohmmeter is crucial to assess condition and safety. Understanding knob and tube systems allows me to pinpoint risks and make upgrades while preserving antique charm.

Armored Cable (AC)

Armored cable (AC) was an early form of metal-clad cable used for wiring in the 1920s-1950s. It consists of two insulated conductors wrapped in paper filler, all enclosed in a spiral steel armor wrapping. The armor grounding conductor served as an equipment grounding path.

Key facts about armored cable wiring:

When I encounter old armored cable, I take care not to damage the aged steel armor to maintain grounding integrity. Understanding how it was installed also helps me make modifications safely.

Conduit Wiring

Conduit wiring systems were widely used from the 1920s onward for commercial and industrial buildings. Rigid metal conduit and boxes house insulated conductors run from device to device.

Key attributes of antique conduit wiring include:

When modifying old conduit systems, I use care not to spread aged wire insulation debris throughout boxes and lines. Knowing tricks like fishing new cables through installed conduits saves major demolition work.

Old-Style Cloth Insulated Wiring

Early electrical systems used insulated cloth-wrapped wiring from about 1880 to 1930. These conductors were single copper wires covered in braided cloth insulation and cotton or cambric tapes.

Key considerations when dealing with antiquated cloth wiring:

When I discover cloth-insulated wiring hidden behind walls, I take extreme care not to disturb it. I explain to customers that it has exceeded its lifespan and should be completely replaced. Handling old cloth-insulated wires demands knowledge and prudence.

Lead-Sheathed Cables

From about 1900 to 1930, lead-sheathed cables provided an early form of armored cable. Insulated conductors wrapped in paper were pulled into a lead pipe sheath.

Working with old lead-sheathed cables requires caution:

When lead-jacketed cables are uncovered in outdated electrical systems, I take steps to isolate and replace them. The materials and methods used require hazardous waste disposal. Working safely avoids lead exposure.


Learning obsolete electrical systems like knob-and-tube, armored cable, cloth-insulated wiring, and lead sheathed cables distinguishes me as an electrician. While daunting at first, recognizing and understanding antiquated methods allows me to take a scholarly approach to servicing older electrical installations. With care and diligence, I can repair and upgrade these historic systems in a cost-effective manner while preserving their legacy charm. Electrical wiring technology has changed tremendously over the decades, but the fundamental principles remain the same. By studying obscure old systems, I gain insights that make me a more knowledgeable and adaptable electrician.