As their teeth continually grow, rodents gnaw on various objects to keep their teeth in shape. Rodents, such as rats, mice and squirrels, tend to have a fondness to sharpen their teeth on electrical cables. It is believed that they like the texture of the PVC against their teeth.
Rodents are flexible, and can get into tiny places, including cavities where cables have been installed. They often expose current and thus heat to the wood beams in the attic, and this is a genuine fire hazard. Once the protective insulation has been chewed off the power cable, we are left with exposed, live wires, carrying electricity around the home. Due to the internal cavities of your home often holding flammable insulation materials, ignition is possible.
Rodents can cause electrical shorts within electrical circuits, or cause fire alarms to activate. Issues that I have come across in both my firefighting and investigation career to date. A simple short, across the exposed conductors will be very unlikely to ignite a fire rather than simply trip the circuit protector. If foreign materials (from saltwater to portion of animal’s anatomy) can sustain circuit flow, the heat generated can degrade the insulation and lead to ignition of the insulation and other fuels in the vicinity.
It is important to note that chewed wiring does not usually mean you have mice in the house, although they have been known to feed on PVC cables. If you spot damaged cables within the attic space in your home, it may mean that you have a bigger rodent squatting in your roof space, a rat or a squirrel for example. It is quite easy to spot a rodent bitten PVC cable – as you can see in the image above, tooth marks are clearly noted.
Rats leave behind calling cards of their appearance, including rat droppings. Mice have similar behaviour traits; however, their droppings are no larger than a grain of rice. Squirrel dropping are like rats; however, squirrels are not as isolated as rats, and may make their presence known by entering properties by doors or windows. So, the chances are, if you have found rodent bitten cables and droppings in your attic, you have rats on the property.
I have been directly involved in the investigation of a large fire which destroyed a factory, with that, a 6-figure financial loss. On attendance to the scene, the large steel structure was heavily fire damages, with roofing structure collapsing in. At the area of origin, by a three-phase roller door switch, the remains of a large rat, which bit through its final cable. The rat bit through a 400 v cable. The spark formed, ignited combustible materials within the locale, which ignited the property.
So how can we prevent such incidents occurring in our own homes? The first thing to know, is which rodent you have on your property; as different rodents have a different type of extraction methods to get rid. I personally would not condone killing the rodents when there are devices out there that can get rid of the rodents humanely. Pest control cages can trap the rodents, with the use of peanut butter and cheese, the rodents can be removed from the property and relocated somewhere exterior.
It is no longer acceptable to run electrical cables in wall cavities of a house due to such problems. Cables should be housed within protective compartments; attic spaces should be kept clean and rodent free. Any holes or crevices in the attic space should be sealed, and rubbish build up around the property to should be kept to a minimum.
In summary: rodents are known to chew on live electrical cables, either short circuiting them directly or leaving the exposed conductors awaiting some other contact. This mechanism probably represents the single most significant contribution to fire causation by animals. The problem with identifying such fire causes as rodent activity, is the destruction of the scene, many fires of this type are misidentified as electrical in origin. We can minimise the chances of such incidents occurring by providing a pest free environment.