# Is knob and tube wiring legal in Massachusetts?

> Is knob and tube wiring legal in Massachusetts? What 527 CMR 12.00 Rule 3 allows, what new work must meet, who may do it, and how code differs from insurers.

URL: https://deckerbostonknobandtube.com/guide/is-knob-and-tube-legal-in-massachusetts/

Yes. Existing knob and tube wiring is legal to keep in service in Massachusetts. Under the state electrical code, 527 CMR 12.00, an installation can be added to or altered while the untouched parts stay as they are, provided the change introduces no new violation and doesn’t deepen one already there. [Decker Boston Knob and Tube](https://deckerbostonknobandtube.com/) arranges knob and tube assessment and replacement in Boston-area homes, carried out by licensed and insured electricians who pull the permits.

“Legal” here answers three separate questions: can the old wiring stay, what happens when someone works on it, and who is allowed to do that work. The sections below take them in turn, then explain why insurers and Mass Save often matter more than the code.

Key takeaways

- The code in force is the 2026 edition of the national code as modified by Massachusetts, covering work permitted after April 24, 2026.
- Rule 3 lets existing wiring stay while new work follows current rules, provided the work doesn’t create or worsen a violation.
- The state’s code committee confirmed that a service with knob and tube circuits can be replaced without replacing those circuits.
- Wiring for hire requires a state electrician’s license and notice to the local inspector of wires.
- No code deadline exists; insurers and Mass Save’s insulation rules are what usually force the decision.

## Which code applies in Massachusetts

The Board of Fire Prevention Regulations publishes the Massachusetts Electrical Code as 527 CMR 12.00. It adopts the 2026 National Electrical Code, with Massachusetts modifications, and applies to installations whose permit was granted after April 24, 2026. The previous edition was built on the 2023 national code.

The national code has an article dedicated to concealed knob and tube. Massachusetts made no amendment to it, so that article applies here as published nationally.

## Can existing knob and tube stay?

Rule 3 is the clause that settles it. Its text says additions or modifications are made under the current code “without bringing the remaining part of the installation into compliance,” and that the installation “shall not create a violation of this Code, nor shall it increase the magnitude of an existing violation.”

### What that means in a house

- Original circuits that are working may stay in service.
- The code does not set a date by which knob and tube must go.
- New circuits, devices and equipment have to meet today’s rules.
- Work that leans on the old wiring is judged by whether it makes things worse.

### The service replacement ruling

In August 2023, under the previous edition, the state’s interpretation committee answered two questions about Rule 3. An electrician who swaps out a service feeding knob and tube circuits may leave those circuits in place, and a solar array may connect to that service too, even with old wiring in poor shape, provided the solar circuits don’t tie into it. The same Rule 3 wording sits in the current edition. The [panel upgrade guide](https://deckerbostonknobandtube.com/guide/does-a-panel-upgrade-remove-knob-and-tube/) explains why a new panel and a rewire are separate jobs.

## What new work has to meet

Replacing knob and tube means installing new circuits, and those follow the current code in full. A few Massachusetts provisions shape the work most.

| Requirement | What it says | Effect on a rewire |
| --- | --- | --- |
| Arc-fault protection | Every 120 volt, 10, 15 and 20 amp branch circuit supplying outlets or devices in a dwelling unit needs it | Each replacement circuit needs an arc-fault breaker or another listed means, which affects panel space ([AFCI and GFCI](https://deckerbostonknobandtube.com/guide/gfci-and-afci-on-knob-and-tube/)) |
| Ground-fault protection | Receptacles within 6 feet of the top inside edge of a sink bowl, or in a cabinet supporting a sink | Kitchen and bath outlets near sinks get GFCI protection |
| Grounding retrofits | Massachusetts deleted the national subsection on equipment-grounding options when non-grounding receptacles are replaced | How that affects a given old circuit is a question for the inspector, not a shortcut to assume ([ungrounded outlets](https://deckerbostonknobandtube.com/ungrounded-outlet-upgrade/)) |
| Cable in finished walls | Cable may be fished between access points where supporting it is impractical | Much of a rewire can run through existing cavities ([plaster wall rewiring](https://deckerbostonknobandtube.com/plaster-wall-rewiring/)) |
| Taller buildings | Above three stories, a nonmetallic-cable circuit has to stay on the floor or in the unit it begins in | Big masonry rowhouses and apartment blocks may call for conduit or armored cable |
| Inspection before covering | Work can’t be concealed until the inspector of wires sees it, within 72 hours of notice for interior work, weekends and holidays excluded | Walls stay open until the rough-in passes (Rule 10) |

The state also left the national code’s arc-fault provision for modified, replaced or extended branch circuits unchanged, so that national text governs work that extends an old circuit.

## Who may work on it

Massachusetts treats wiring as licensed work, and the rules are specific about who files and who is responsible.

- **Licensing:** under M.G.L. c. 141, § 1A, installing wires for light, heat or power as a business requires a license from the Board of State Examiners of Electricians.
- **Notice to the inspector:** M.G.L. c. 143, § 3L requires anyone installing wiring for hire to notify the local inspector of wires before starting or within five days after, with a fine of up to $500. The installer reports completion, and the inspector approves or disapproves in writing within five days.
- **Boston:** Inspectional Services accepts electrical permit applications only from licensed contractors, and tells homeowners to hire one for both the filing and the work ([Boston permit guide](https://deckerbostonknobandtube.com/guide/boston-electrical-permit-for-rewiring/)).
- **Nearby cities:** Somerville’s inspectional services likewise reserves electrical permits for licensed electricians, and Cambridge, Medford and the rest each keep their own wire office.

## Code, insurers and Mass Save are three different authorities

Owners often hear “it has to come out” and assume the code said so. Usually it didn’t.

| Authority | What it can require | Basis |
| --- | --- | --- |
| State electrical code | New work done to current rules, without creating or worsening a violation | 527 CMR 12.00 |
| Insurance carrier | Removal, proof the wiring isn’t live, or a deadline, as a condition of coverage | The carrier’s own underwriting ([insurance guide](https://deckerbostonknobandtube.com/guide/knob-and-tube-insurance-massachusetts/)) |
| Mass Save | No insulation where knob and tube is present until a licensed electrician addresses it and certifies the work areas | Mass Save’s assessment standards ([insulation barrier](https://deckerbostonknobandtube.com/knob-and-tube-insulation-barrier/)) |

## When legal still isn’t the end of it

The code describes what is allowed, not what is wise for a particular circuit. Rule 3 protects working wiring; it doesn’t certify that a cracked, overfused or buried-splice run is safe. The [danger guide](https://deckerbostonknobandtube.com/guide/is-knob-and-tube-wiring-dangerous/) covers which conditions turn old wiring into a hazard, and an [inspection](https://deckerbostonknobandtube.com/knob-and-tube-inspection/) shows which ones a house has.

For a reading of how these rules apply to your own circuits and project, phone Decker Boston Knob and Tube on [(617) 405-3599](tel:+16174053599) or [request an estimate](https://deckerbostonknobandtube.com/contact/).

## Questions about this guide

### Does Massachusetts have a grandfather clause for knob and tube?

Not under that name. What people mean is Rule 3 of 527 CMR 12.00, which lets additions and modifications be made without bringing the rest of an existing installation into compliance, provided the new work doesn't create a violation or increase an existing one. Working knob and tube can therefore remain in service, but anything new connected to it has to meet the current code.

### Can an inspector make me remove knob and tube during another project?

Not simply because it exists. The inspector of wires judges the work on the permit, and under Rule 3 that work can't introduce a violation or deepen one already present. If a project would extend or load an old circuit in a way that does, the inspector can refuse to approve it. Ask your electrician how the planned work touches the old circuits before the permit is filed.

### Does the Massachusetts code allow insulation over knob and tube?

The state adopted the National Electrical Code's article on concealed knob and tube without amendment, so that article's own limits govern. In practice the rule owners actually meet is Mass Save's: no insulation goes in where knob and tube is present until a licensed electrician addresses it.

Want this answered for your house?

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## Related service

### Knob and Tube Inspection →

A licensed electrician traces every circuit, finds which old runs still carry power and puts the findings and a recommended scope in writing.

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