Direct answer: Chewed wires under a subfloor are not a watch-and-wait problem. If copper is exposed, insulation is torn, or a breaker has tripped, shut off the affected circuit and keep people out of the area until the wiring is properly repaired.
Most likely: The usual situation is rodent damage to NM cable or individual conductors in a crawlspace or basement ceiling, often near warm runs, entry points, or stored nesting material.
Start by deciding whether this is an active hazard or a discovered old problem. Fresh chew marks, droppings, a hot smell, flickering, dead outlets, or a breaker that will not stay on all move this into urgent territory. Reality check: if an animal got to one cable, there may be more damage nearby than the first spot you saw. Common wrong move: fixing the visible bite marks and missing the second damaged section a few feet away.
Don’t start with: Do not start by taping over bite marks, pushing the cable back in place, or resetting a tripped breaker repeatedly.
Cable jacket is nicked or shredded, but lights and outlets on that circuit still seem normal.
Start here: Treat it as unsafe anyway. Hidden conductor damage can arc later even if the circuit is still carrying power.
A breaker is off, trips again right away, or trips after a short delay when you try to restore power.
Start here: Leave that breaker off. This strongly suggests conductor damage or a short to ground/neutral somewhere on the run.
Power comes and goes, especially when someone walks above, a fan runs, or the cable is disturbed.
Start here: Stop using that circuit. Intermittent power with damaged wiring points to loose or partially severed conductors.
You smell hot plastic, hear faint crackling, or feel warmth near the cable or nearby wood.
Start here: Shut off power immediately and do not keep inspecting around energized wiring. This is a same-day electrician situation.
Mice and rats commonly chew NM cable jackets and insulation, especially in crawlspaces, basements, and quiet joist bays.
Quick check: Look for paired tooth marks, shredded paper or insulation, droppings, and damage concentrated along accessible runs.
The outside jacket can look only lightly damaged while the copper inside is nicked or nearly cut through, causing flicker, heat, or nuisance trips.
Quick check: If the cable feels flattened, sharply bent, or deeply gouged, assume internal conductor damage even if you cannot see bare copper.
Animals usually travel a route, not a single point. One obvious chew area often means more damage near penetrations, insulation edges, or along the same joist line.
Quick check: Follow the cable visually in both directions with power off and look for repeated tooth marks, sagging sections, or disturbed staples.
In crawlspaces, wet wood, condensation, or urine contamination can make damaged insulation more dangerous and can trip protection devices sooner.
Quick check: Check for damp framing, wet insulation, staining, or stronger odor around the damaged section without touching the cable.
Before you inspect anything else, you need the damaged wiring de-energized and you need to know whether this has already crossed into immediate fire-risk territory.
Next move: The area is de-energized and there are no active heat or smoke signs, so you can do a careful visual check only. If you cannot identify the circuit safely, the tester still shows voltage, or you have heat, smell, smoke, or noise, stop here and call an electrician now.
What to conclude: This tells you whether you are dealing with a discovered damage issue or an active fault that needs same-day professional repair.
The first visible chew mark is often not the whole story. You want the full damaged zone before anyone plans a repair.
Next move: You can tell whether this is one localized damaged section or a longer run with repeated damage. If the cable disappears into finished areas, insulation, or tight framing and you cannot confirm the full extent, plan on professional tracing and repair.
What to conclude: A short, fully visible damaged section may be straightforward for an electrician to replace. Hidden or repeated damage raises the odds of a larger rewire section.
This helps separate a discovered hazard from a fault that has already opened the circuit or damaged connected devices.
Next move: You have a clearer picture of whether the damage caused an outage, intermittent fault, or just has not failed completely yet. If symptoms spread beyond one obvious circuit, or you cannot tell what the cable serves, the repair needs circuit tracing by a pro.
For damaged fixed house wiring under a subfloor, most homeowners should stop at safe shutdown and inspection. The repair usually involves replacing damaged cable sections, opening boxes, or adding accessible junction points correctly.
Next move: You avoid the common mistake of making a hidden patch on permanent wiring and you give the electrician a clean, accurate scope. If you are tempted to energize the circuit because it 'mostly works,' stop and leave it off until repaired.
Restoring power safely means fixing the wiring first and reducing the chance of repeat damage right after the repair.
A good result: The circuit runs normally, the damaged area is properly repaired, and the animal access issue is being addressed.
If not: If symptoms return after repair, there is likely more hidden damage on the same circuit or another nearby run.
What to conclude: A lasting fix is both electrical repair and pest-route control. Doing only one of those usually brings the problem back.
No. Tape is not a proper repair for damaged fixed house wiring. If the jacket or conductor insulation has been chewed, the damaged section usually needs to be replaced or reworked by an electrician.
It can still be unsafe. Rodent damage often nicks insulation or copper without causing an immediate outage. Those are the jobs that surprise people later with arcing, flicker, or a hot smell.
It is urgent if you have exposed copper, a tripped breaker, flickering, burning smell, buzzing, heat, or wet conditions. If you only discovered old-looking chew marks with no active symptoms, it is still a leave-it-off-until-repaired issue, just not the same level as smoke or odor.
Best practice is no. If the cable has visible chew damage, leave that circuit off. Re-energizing damaged wiring under a floor is not worth the fire risk just to get temporary use back.
Usually not. They tend to travel a route. When I find one chewed section, I expect to inspect the nearby run, penetrations, and adjacent bays for more damage before calling it done.
That depends on your policy and the cause of loss. Document the damage with photos, note any affected circuits, and ask your insurer what they require before cleanup or repair changes the scene.