# How does knob and tube replacement work, from the first visit to the final inspection? > How knob and tube replacement works in an LA house: circuit map, plan, permit, attic and crawlspace routing, inspection and patching. Start with a walk-through. URL: 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. Last Updated: October 24, 2026 [LA Knob and Tube](https://laknobandtube.com/) replaces knob and tube wiring across Los Angeles, Pasadena, Glendale and South Pasadena, and this is how knob and tube replacement works on a typical job. A circuit map comes first. It becomes a rewiring plan and a quote. The city permit is pulled, then circuits are replaced in sequence through the attic and crawlspace, old runs are disconnected, the inspector checks the work, and openings are closed as the quote describes. The order matters more than any single step. A route cannot be planned before the circuits are known, the walls cannot be closed before the inspector has seen the wiring inside them, and the old wiring cannot be called retired until someone has confirmed it is dead. ## 1. Inspection becomes a circuit map The first visit answers which outlets, lights and appliances still depend on knob and tube, and whether each old run is live, abandoned or mixed with later wiring. It starts at the panel, then moves to the attic and crawlspace, where the accessible runs and splices are traced, and then room by room, matching each device to its circuit. The [knob and tube inspection](https://laknobandtube.com/knob-and-tube-inspection/) page describes that visit, and the guide to [active and abandoned knob and tube](https://laknobandtube.com/guide/active-vs-abandoned-knob-and-tube/) explains how live and dead runs are told apart. The same visit measures access: crawlspace height, attic clearance and insulation, wall finishes, and where a route has no open space above or below it. Without both halves, the circuits and the access, nothing after this point can be priced honestly. ## 2. The circuit map becomes a rewiring plan The map shows what the house has; the plan decides what it should have. An original layout might feed half a house from two or three circuits. The plan usually spreads those loads across more circuits, adds dedicated circuits where the code calls for them, such as kitchen counters, bathrooms and laundry, and places new outlets so extension cords are no longer needed. The plan also sets the order of work. Circuits are grouped so that each day only a few are off and the rest of the house keeps power. Where a [panel upgrade](https://laknobandtube.com/electrical-panel-upgrade/) is part of the job, it is scheduled so new circuits land on new breakers. The plan names every planned opening and who closes it, which is what the quote is built from. The [rewiring quote checklist](https://laknobandtube.com/guide/rewiring-quote-checklist/) lists what that quote should spell out. ## 3. The permit Rewiring is permitted work. In the City of LA, LADBS issues the electrical permit, and nearly every house rewire permit is issued as an express permit without plan check. Pasadena, Glendale and South Pasadena issue their own. The permit has to exist before an inspector will come out, so it is pulled before the walls are touched. The [Los Angeles rewiring permit guide](https://laknobandtube.com/guide/los-angeles-rewiring-permit/) covers who can pull it. ## 4. Choosing the material for each run The material follows the location. Inside dry wall and ceiling cavities and along attic framing, the usual choice is NM-B cable, which carries a hot conductor, a neutral and a bare equipment ground in one jacket. That ground is the part knob and tube never had. Where a run is exposed to physical damage or moisture, cable alone is not enough. Along a garage wall, on the outside of the house, or wherever the code requires protection, individual THHN/THWN conductors are pulled through electrical conduit, or armored cable is used. The choice depends on the run, the code and the inspector, not on one method suiting every house. ## 5. Routing new cable: where the path splits New cable routing is where the job depends most on the building. In a house on a raised wood floor with a tall, clear crawlspace, first-floor outlets are usually fed from below, up through the bottom plate of the wall. Ceiling lights and switches are usually fed from the attic, down through the top plate. In that best case, most of the work happens above and below the rooms. The path changes when: - **The crawlspace is shallow or blocked** by ducts, pipes or debris, so some outlets have to be reached from above or through a wall opening. - **The attic is packed with insulation** or has finished space, so ceiling work moves slower and may need ceiling openings. - **The house has a second story,** whose floor has no open space beneath it, so routes run through closets, chases or strategic openings. - **A route crosses framing,** such as a fire block, a header over a doorway or a beam, and an opening is needed at that point. - **Walls are plaster on lath,** which is opened and patched differently from drywall; the [plaster wall rewiring](https://laknobandtube.com/plaster-wall-rewiring/) page explains how routes are chosen to keep openings small. Each opening is planned, not improvised, and its location goes on the list the quote describes. ## 6. Rewiring reaches the receptacles and switches Every new circuit ends at devices: outlets, switches, fixtures and appliance connections. Old boxes are often shallow and have no way to connect a ground, so many are replaced with boxes sized for modern cable and devices. New receptacles in dwellings are tamper-resistant. Replaced circuits in living areas get arc-fault protection, either an AFCI breaker or an outlet-type AFCI at the first receptacle, and kitchens, bathrooms and other wet locations get GFCI protection. The [AFCI and GFCI guide](https://laknobandtube.com/guide/afci-gfci-knob-and-tube/) explains both. Connections at the panel come last for each circuit: the new cable is landed on a breaker sized for it, and the panel directory is labeled so each breaker names the rooms it feeds. ## 7. Old circuits are isolated, then verified As each new circuit is energized, the knob and tube run it replaces is disconnected at both ends, at the source and at the last device, so it cannot be fed again by accident. Then the disconnection is verified with a tester, because an old run can be fed from more than one point where it was spliced into another circuit years ago. Accessible abandoned runs can be removed; the [knob and tube removal](https://laknobandtube.com/knob-and-tube-removal/) page covers that decision. ## 8. Testing and inspection Before the inspector arrives, the new circuits are tested: polarity, ground continuity, and that AFCI and GFCI devices trip as they should. The inspector checks the wiring before walls and ceilings are closed, then again at the end. A correction notice means fixing the item and calling the inspector back. The final sign-off is the record an insurer or a buyer usually asks to see; the [California insurance guide](https://laknobandtube.com/guide/knob-and-tube-insurance-california/) covers what carriers ask for. ## 9. Openings are restored Only after the inspector has seen the work inside a wall can that opening be closed. Plaster patches take more steps than drywall, and texture and paint are a separate decision. The quote should already say who does each: closing the opening, matching texture, and painting. ## 10. The paperwork you keep At the end, the house should have a labeled panel, the permit with its final inspection, and, on a [partial replacement](https://laknobandtube.com/partial-knob-and-tube-replacement/), a written list of every circuit that still runs on knob and tube. That list is what stops a partly rewired house from being described as fully rewired at a sale or after a claim. For what this looks like day to day, the guide to [living at home during a rewire](https://laknobandtube.com/guide/living-at-home-during-rewiring/) covers power, dust and scheduling. When you want your own house mapped, call or request an estimate, and the first visit starts at the panel. ## Questions about this guide ### What cable replaces knob and tube in a typical rewire? Inside dry framing, usually NM-B cable, which carries a hot, a neutral and a bare ground in one jacket. Where a run is exposed to damage or moisture, conductors such as THHN/THWN are pulled through conduit, or armored cable is used, as the code requires. ### Why are old outlet boxes often replaced during a rewire? Boxes from the knob and tube era are often shallow, unsized for modern devices and cable, and have no way to bond a ground. A new box fits the new cable, the grounded device and any AFCI or GFCI device the circuit needs. ### Can new circuits follow the old knob and tube routes? Often in part. The original runs usually travel through the attic and crawlspace and drop into walls where outlets are. New cable can take similar paths, but it is routed for the new circuit layout, not traced along every old wire. ## More guides - Learn [How long does rewiring take, and can you live at home while it happens?](https://laknobandtube.com/guide/living-at-home-during-rewiring/)The schedule depends on circuits, access and inspections. Here is what decides it, and what an occupied house should plan for. - Decision Guide [What should a rewiring quote include, and how do you compare two of them?](https://laknobandtube.com/guide/rewiring-quote-checklist/)Two quotes for the same house can be thousands apart because they describe different jobs. This list shows what to look for and how to line them up. - Learn [Do you need an electrical permit for rewiring in Los Angeles, and how does it work?](https://laknobandtube.com/guide/los-angeles-rewiring-permit/)Who issues it, who is allowed to pull it, what the inspector checks, and how Pasadena, Glendale and South Pasadena differ from LADBS. - Decision Guide [Panel upgrade vs rewiring: which one does an older house need, and when does it need both?](https://laknobandtube.com/guide/panel-upgrade-vs-rewiring/)They are separate jobs on separate parts of the system. Here is how to tell which one your house needs, and how they fit together when it needs both. - Decision Guide [Is knob and tube still active in your house, or abandoned?](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.