# Is knob and tube still active in your house, or abandoned? > Is knob and tube still active in your house? How an electrician confirms live, dead and mixed wiring, and why it matters to insurers. Start with a circuit map. URL: https://laknobandtube.com/guide/active-vs-abandoned-knob-and-tube/ How live, dead and mixed wiring is told apart, why the answer is rarely visible, and what it changes for an insurer, an insulation job and removal. Last Updated: October 24, 2026 Usually you cannot tell by looking. Knob and tube is active if any of its conductors still carry current, even a short stretch feeding modern outlets. It is abandoned only when disconnected at both ends. Confirming which takes an electrician tracing circuits from the panel and testing them, because live, dead and mixed runs look identical. [LA Knob and Tube](https://laknobandtube.com/) replaces knob and tube wiring across Los Angeles, Pasadena, Glendale and South Pasadena, and the first visit on every job maps live, dead and mixed circuits before anything is quoted. This guide explains the four states old wiring can be in, how a professional tells them apart, and why the answer changes what an insurer, an insulation contractor and a removal plan need. Key takeaways - Active, abandoned, partial and mixed are different states with different consequences - Live and dead runs look identical; only tracing and testing tells them apart - A modern outlet can be fed by a knob and tube run upstream - Abandoned means disconnected at both ends, and documented - Insurers, insulation rules and removal plans all turn on the answer ## Four states, not two **Active** knob and tube is energized and in use: it carries current to lights and outlets today. **Abandoned** knob and tube is disconnected at both ends and can no longer be energized; it may still be in the walls or attic, but it is dead. A **partial** system is a house where some circuits have been replaced and others are still original and live. A **mixed** system is a house where old and new wiring are joined on the same circuit, for example modern cable spliced into an original run in the attic, so a new outlet depends on old conductors upstream. Partial and mixed systems are where most of the confusion sits, because a house can look rewired from every room and still have active knob and tube carrying part of the load. ## Why you cannot tell by looking A live conductor and a dead one look the same. Both have the same cloth braid on the same porcelain knobs. An old run that was cut at the panel decades ago may still be connected, through a splice in the attic, to a circuit that was later extended. A run that looks original from the hatch may be the one remaining feed to three bedrooms. The visible clues in the [identification guide](https://laknobandtube.com/guide/how-to-identify-knob-and-tube/) tell you that knob and tube is present. They cannot tell you whether it is active. And a non-contact tester waved near a run is not an answer either: it can read false positives and negatives, and it means getting close to wiring that should not be disturbed. ## How a professional confirms live or dead The work happens in an order, and it starts at the source. 1. **The panel or fuse box.** Each circuit is identified: what it feeds, what size fuse or breaker protects it, and what kind of wire leaves the panel. Knob and tube conductors connected at the panel are a direct sign the circuit is active. 2. **Mapping outlets and lights to circuits.** Circuits are switched off one at a time to see which rooms go dark, or a circuit tracer is used to follow a signal from the outlet back to the panel. The result is a map of which rooms depend on which circuit. 3. **Tracing the runs.** In the attic and crawlspace, accessible runs are followed from the panel feed toward the rooms, noting where they split, where modern cable joins them and where runs end in cut or capped conductors. 4. **Testing.** With proper meters and protective equipment, the electrician tests whether old conductors carry voltage, both with circuits on and with the suspected feed off. A run that stays dead with everything on, and has no connection to anything live, is a candidate for abandoned. 5. **Writing it down.** The findings become a circuit list: which circuits are active knob and tube, which are mixed, which are modern, and which old runs are dead. All of this involves opening panels and testing energized conductors, which is electrician’s work. It is part of a [knob and tube inspection](https://laknobandtube.com/knob-and-tube-inspection/), and it has a limit: runs inside closed walls can be inferred from where they start and end, but not seen. ## Mixed systems: the part that causes trouble In a house that has been remodeled, the finding that matters most can be a mixed circuit. A remodel adds modern cable for new outlets and ties it into the nearest original run in the attic, because that was the easiest source of power. Every outlet on that new cable now depends on the old conductors, the old splice and the old fuse rating upstream. The room looks modern, and the outlets may even be grounded locally, but the circuit is still knob and tube where it matters most. Mixed circuits also hide shared or crossed neutrals, where one circuit’s current returns on another’s neutral. That shows up when new GFCI or AFCI devices trip for no obvious reason, as the [AFCI and GFCI guide](https://laknobandtube.com/guide/afci-gfci-knob-and-tube/) explains. ## Why the answer matters ### For insurance The question homeowners and agents report carriers asking is whether any knob and tube is still energized. A house where every old run is disconnected at both ends, with a permit and an electrician’s letter to show it, answers that question differently from a house with one live mixed circuit in the attic. Carriers differ, so ask yours in writing what it needs; the [insurance guide](https://laknobandtube.com/guide/knob-and-tube-insurance-california/) covers the questions and the letter. ### For attic insulation California’s electrical code bars insulation that envelops concealed knob and tube in attics and walls unless a California-licensed electrical contractor surveys and certifies the wiring first. Whether dead runs are treated differently from live ones is a question for the building department, and the answer depends on being able to show that they are disconnected. Replacing the attic circuits and documenting the old runs as abandoned is often the simpler path, which the [attic insulation page](https://laknobandtube.com/knob-and-tube-attic-insulation/) explains. ### For removal Abandoned runs do not have to come out. Runs inside closed walls are usually left in place, dead, because removing them means [opening plaster](https://laknobandtube.com/plaster-wall-rewiring/) for no electrical benefit. Accessible runs in the attic and crawlspace can be pulled out, which is worth doing when insulation, storage or a [seismic retrofit](https://laknobandtube.com/guide/seismic-retrofit-and-rewiring/) is coming. The [knob and tube removal](https://laknobandtube.com/knob-and-tube-removal/) page covers that choice. What matters more than removal is that every replaced run is disconnected at both ends, so it cannot be re-energized by accident. ## What a finished job leaves you with After replacement, the house has a labeled panel, a permit with final inspection and, on partial jobs, a written list of the circuits that remain on knob and tube, with the rooms they serve. That list is what turns “we think it’s all dead” into something an insurer, a buyer’s inspector or a future electrician can rely on. If you are buying, the [buying guide](https://laknobandtube.com/guide/buying-a-house-with-knob-and-tube/) explains how to get the answer before contingencies end, and the [replacement process guide](https://laknobandtube.com/guide/knob-and-tube-replacement-process/) shows where disconnection fits in the sequence. If you are not sure whether the knob and tube in your attic is live, call and ask for a circuit map. It is the first thing the visit produces. ## Questions about this guide ### Can a dead knob and tube run become live again? Yes, if it was only disconnected at one end. A run cut at the panel can still be connected to a live circuit at a splice further along, or reconnected by later work. That is why replaced runs are disconnected at both ends, at the source and at the last device, and documented. ### Who can confirm that knob and tube is disconnected? A California-licensed electrical contractor, after tracing and testing the circuits. A general home inspector can note that knob and tube is present but usually cannot confirm whether it is live. If your insurer asks, find out in writing whether it wants a letter and who must sign it. ### Does a mixed system count as active knob and tube for an insurer? Usually, if any knob and tube conductor still carries current, including a short section feeding modern cable downstream. Carriers word their questions differently, so ask yours in writing and have the electrician answer in the same terms. ## Related service ### Removal Disconnect old runs for good, prove they are dead, and pull out the ones that are worth removing. ## More guides - Learn [How do you identify knob and tube wiring?](https://laknobandtube.com/guide/how-to-identify-knob-and-tube/)A look-only guide to the clues in attics, crawlspaces, fuse boxes and rooms, and why what you can see is never the whole answer. - Learn [How does knob and tube affect home insurance in California?](https://laknobandtube.com/guide/knob-and-tube-insurance-california/)What carriers tend to ask, how to get their answer in writing, what an electrician's letter can and cannot say, and where the FAIR Plan fits. - Learn [Is knob and tube wiring dangerous?](https://laknobandtube.com/guide/is-knob-and-tube-wiring-dangerous/)How the risk develops in old wiring, which signs mean a circuit should go off today, and what nobody can know about your house without seeing the wiring. - Decision Guide [What should you know before buying a house with knob and tube?](https://laknobandtube.com/guide/buying-a-house-with-knob-and-tube/)How to fit an electrical evaluation, an insurance answer and a negotiation into the time escrow gives you. - Learn [How does knob and tube replacement work, from the first visit to the final inspection?](https://laknobandtube.com/guide/knob-and-tube-replacement-process/)Each stage depends on the one before it. Here is what has to be known before the next step starts, and where the path splits by house.