You’ve heard knob and tube is “against code” and you’re wondering whether your house is breaking the law. It isn’t. Existing knob and tube isn’t unlawful in Minnesota just because of its age. Minnesota adopts the National Electrical Code without amendment, and that code still has an article for concealed knob and tube. What the code does is limit the system: it can’t spread freely, it can’t sit in insulation, and anything new has to meet today’s rules.
At Northloom Minneapolis Knob and Tube, we replace knob and tube across Minneapolis and St. Paul. This guide explains what the code means for your house, who checks it here, and why legality is rarely the thing that decides what happens to your wiring.
Can I leave my knob and tube alone?
Yes, as long as it’s in good condition and nobody is changing it. Electrical codes generally apply to work when it’s done, not backward. Wiring put in correctly under the rules of its day isn’t made illegal by a later edition. The moment new work touches it, though, the new work has to meet the current code.
That gives you four situations, and each has its own answer.
- You leave it alone
- Existing knob and tube in good condition can stay in service.
- You extend it
- Allowed only as an extension of an existing installation, and never through an insulated space.
- You replace it
- The new circuits have to meet the current code in full.
- You insulate around it
- Not allowed while it’s live.
So the real question for most homeowners isn’t “is it legal” but “what am I about to do to the house.” A remodel, new insulation or a sale is usually what brings the code into it.
What does the code actually say about it?
Minnesota adopts each new edition of the National Electrical Code statewide, currently without amendment. The code’s article on concealed knob and tube does three things that matter to you.
| The rule | What it means in your house |
|---|---|
| Use is limited to extending existing installations, or elsewhere with special permission | Nobody installs new knob and tube systems; a short extension of yours is possible but rarely sensible |
| It can’t be used in hollow spaces with loose, rolled or foamed insulation surrounding the conductors | You can’t insulate walls or attics around live knob and tube |
| New circuits meet the current code | New work gets a ground, arc-fault and ground-fault protection where the code lists it, and proper boxes |
The bar on insulation isn’t new. A 1987 change to the code first barred insulation in contact with knob and tube, and it has stayed in every edition since. That one rule is why so many Minneapolis attics stay cold until the wiring is settled.
Who checks the wiring where I live?
Whoever issues electrical permits for your address enforces the code there.
| Where you live | Who handles electrical inspection |
|---|---|
| Minneapolis | Minnesota Department of Labor and Industry |
| St. Paul | City of Saint Paul Department of Safety and Inspections |
| Other cities | The state, or one of about 66 Minnesota cities that run their own electrical inspection |
Inspectors see new work. They don’t walk through a house nobody is working on and look at its old wiring. That’s why knob and tube can sit in a house for decades with nobody citing it, and why it surfaces the day a remodel, an insulation job or a sale brings someone in. The permit guide walks through the process.
Why does everyone else seem stricter than the code?
Because they’re answering a different question. The code asks whether work was done correctly. Insurers, buyers and insulation contractors ask whether they’re comfortable taking on the house. Each can set a higher bar.
- Your insurer
- Many carriers ask whether any knob and tube is energized, and some won’t write a new policy until it’s replaced or documented as inactive. For a policy in force, Minnesota’s rules require two written requests before nonrenewal over a known condition.
- A buyer and their lender
- The buyer’s inspector notes it, and the buyer’s lender or insurer may require action before closing.
- Your insulation contractor
- They generally won’t insulate around live knob and tube, in line with the code’s bar.
- City sale reports
- Reports such as St. Paul’s Truth-in-Sale of Housing report disclose wiring conditions to buyers.
The homeowners insurance guide covers how carriers handle it.
Can I do the work myself?
Sometimes. Minnesota law governs who may do electrical work, separately from what the code says about the wiring.
- Work for someone else
- Minnesota requires a license to do electrical work for another person, and the license holder files the request for inspection.
- Homeowner permits
- A deeded owner living in a single-family house can get a homeowner permit to do their own work there. It can’t be used on a duplex or other multi-unit building.
- Request before work
- The request for electrical inspection is filed at or before the start of work.
- Work without a request
- Work begun without it carries a state investigation fee on top of the permit, of up to $1,000.
- Inspection before covering
- New wiring is inspected at rough-in, before plaster, drywall or insulation covers it.
These rules apply whenever knob and tube is replaced or extended. That’s why “is it legal” so often turns into “who does the work, and under which permit.” When you hire us, getting the permit in place is part of the job.
What if it’s a rental?
The same questions apply, one unit at a time. Landlord policies often ask whether any knob and tube is energized, and a city’s rental rules may set their own standards for wiring; we confirm those for each property. Minnesota’s homeowner permit can’t be used on a duplex or other multi-unit building, so rental work goes under a licensed contractor’s permit, with the residents’ schedules planned in.
When does this usually come up?
At a few predictable moments. A remodel opens walls and the inspector sees original wiring beside the new work. An insulation contractor declines to insulate around it. A buyer’s inspector writes it up. Your insurer sends a letter.
In each case the useful answer is the same: trace the circuits, settle what’s live, and plan any new work to the current code. The code rarely forces the decision on its own, but every one of those moments involves new work or a third party who applies it.
What do people get wrong about the rules?
| What people believe | What’s actually true |
|---|---|
| “Knob and tube is illegal now.” | Existing installations aren’t outlawed; new installations are limited |
| “A new panel brings the house up to code.” | A panel changes the source; the branch circuits behind it stay as they were |
| “Three-prong outlets mean it’s grounded.” | Only if there’s a real ground behind them, or GFCI protection with the required labels |
| “It passed inspection years ago, so it’s fine.” | The original job may have been fine; later splices, insulation and loads may not be |
| “The city will make me replace it.” | Usually an insurer, a buyer or an insulation project drives replacement |
So what should I do next?
Knowing it’s legal doesn’t tell you what to do with it. The questions that matter are whether it’s live, what shape it’s in, and what your insurer, a buyer or your insulation contractor needs. Our knob and tube inspection answers the first two, and the guide to whether knob and tube is dangerous explains which conditions matter. If you’d like to talk through your house: (612) 509-6597.