Mice have chewed through wiring: how serious it is and what to do

Why mice gnaw at cables and where you tend to find it

Mice gnaw to keep their front teeth worn down, and cable insulation is soft enough to be an easy target. It is not the electricity that attracts them, it is the shape and the material, which is why data cables and phone lines get chewed just as readily as mains wiring.

In Tallinn this shows up most often in older wooden houses in Kalamaja and Nõmme, where cables run through timber floor voids, wall cavities and lofts that mice can reach easily. Ground-floor flats in panel buildings get it too, usually where cabling runs behind kitchen units or through a service duct near an exterior wall.

Typical signs are frayed or missing insulation over a short stretch, small dark droppings nearby, and sometimes a scratching noise in the same spot at night. If you have found one chewed cable, it is worth assuming there may be others along the same run.

What makes exposed copper genuinely dangerous

Insulation exists to keep the conductor away from anything it could touch, including other wires, metal fixings, damp timber or a curious hand. Once it is gone, a bare live conductor can arc against a nearby surface, and that arc can be hot enough to ignite dust, insulation debris or dry wood nearby.

A chewed cable can also develop an intermittent short, which is harder to notice than a dead circuit. You might see a fuse or breaker trip occasionally, lights flicker for no obvious reason, or a socket feel slightly warm, all of which are worth taking seriously rather than dismissing as a one-off.

The risk is worse in exactly the places mice like: crawl spaces and lofts full of dry timber and stored boxes, and cavities behind cabinets where you would not notice a problem developing until it is well advanced.

What to do straight away if you find a chewed cable

Do not touch the exposed section, and do not try to test it by switching the circuit on and off. If you can safely identify which breaker or fuse serves that circuit, switch it off at the consumer unit. If you are not sure which one it is and the damage looks fresh or severe, switch off the main isolator instead.

Take a few photos of the damage before you do anything else, since these help enormously when describing the problem over the phone or by email. Keep pets and children away from the area, particularly in a loft or under-floor space where the chewed section might not be easy to see.

This is exactly the kind of job where our round-the-clock availability for urgent electrical problems is worth using, since a chewed live cable is not something to leave until a convenient afternoon. Electrical work is charged from 49 € per hour, with a minimum of one hour.

• Switch off the relevant breaker, or the main isolator if unsure
• Do not touch or tape the exposed cable
• Photograph the damage for reference
• Keep the area clear of people and pets
• Call for an assessment rather than waiting

Why tape is not a fix and the whole section has to come out

Insulation tape can look like a reasonable stopgap, but it does not restore the cable's rated protection, it is not fixed against a specific standard for cable repair, and it does nothing about damage further along the run that you cannot see. Mice rarely chew one neat spot and stop.

The correct approach is to trace the cable back to sound insulation on both sides of the damage and replace that entire section, joining it properly at an accessible point such as a junction box rather than leaving a taped joint buried in a wall cavity or floor void.

This is electrician's work, not a DIY repair, because it involves identifying the circuit correctly, isolating it safely, and making a joint that will hold up for years rather than months. If the consumer unit itself is old or the damaged circuit reveals wider problems with the board, a consumer unit replacement, from 350 € per job, is sometimes the more sensible next step.

When a check is enough and when you need something more thorough

A single chewed cable found early, with clean electrical checks either side and no sign of further rodent activity, often just needs that one section replaced and isolation confirmed. That is a straightforward job, usually an hour or two of work plus materials.

If you find chewed cables in more than one place, if there is visible rodent activity such as droppings or nesting material in the same void, or if the property has had mouse problems before, it is worth having the wider run inspected rather than treating each cable as a separate incident.

The same goes for older wiring in general: if the chewed section turns out to sit on ageing rubber or fabric-sheathed cable rather than modern PVC insulation, that is a different and broader question about the age of the installation, which is worth raising separately when the electrician is on site.

Stopping mice coming back to the same spot

Repairing the cable solves the immediate danger, but if the entry point that let the mice in is still open, the same run or the one next to it can get chewed again within a few months. Once the electrical work is done, it is worth finding and sealing the gap the mice used, commonly around pipe penetrations, gaps under skirting, or where a foundation meets timber cladding.

Steel wool packed into small gaps and sealed over with mastic or expanding foam is a reasonable barrier, since mice cannot gnaw through it easily. Traps or bait in the affected void, placed away from the repaired cable, deal with mice already inside rather than just the entry point.

In wooden houses with a ventilated crawl space, checking that access hatches close properly and that stored materials do not create a warm, undisturbed nesting spot near the wiring run makes a repeat problem noticeably less likely.