Electrical fires kill hundreds of Americans every year and cause billions of dollars in property damage. According to the National Fire Protection Association, electrical distribution equipment -- the wiring, panels, outlets, and connections inside your walls -- is one of the leading causes of home structure fires. And within that category, arc faults are the single most dangerous mechanism. They start fires in places you cannot see, at temperatures that ignite wood framing in fractions of a second, and they do so at current levels that your standard circuit breaker considers perfectly normal.
Understanding what arc faults are, how they start fires, and why conventional breakers cannot stop them is essential knowledge for every homeowner -- especially if you live in an older home where the wiring has had decades to deteriorate.
What Exactly Is an Arc Fault?
An electrical arc is a discharge of electricity through the air between two conductors. You have seen small, harmless arcs many times: the tiny spark that occurs when you unplug a running appliance from an outlet, or the brief flash when a light switch is flipped. These are normal arcs that occur during the making and breaking of electrical connections. They last a fraction of a second and dissipate harmlessly.
A dangerous arc fault is fundamentally different. It is a sustained, unintended discharge of electricity across a gap in a damaged conductor or between two conductors whose insulation has failed. Unlike the momentary spark of unplugging a cord, an arc fault can sustain itself for seconds, minutes, or even hours, generating extreme heat at the point of arcing. The temperature at the arc point can exceed 10,000 degrees Fahrenheit -- roughly twice the temperature of the surface of the sun. At that temperature, wood framing, insulation, drywall paper, and virtually any other building material in contact with or near the arc point will ignite almost instantly.
Series Arc Faults: The Hidden Fire Starter
A series arc fault occurs along a single conductor -- a single wire that has been damaged, creating a gap or high-resistance point through which current must arc to complete the circuit. Think of it as a break in the wire where electricity is forced to jump across the gap rather than flow smoothly through intact copper.
Series arc faults are caused by physical damage to wiring. A nail or screw driven through a wall during a picture-hanging project can nick or partially sever a wire inside the wall. Rodents gnaw on wire insulation in attics and crawl spaces, exposing and damaging the conductor underneath. Wiring that passes through a hole in a framing member can be abraded over time by vibration, especially near HVAC equipment. Old wiring with deteriorated insulation can develop internal breaks as the copper becomes brittle with age.
The insidious nature of a series arc fault is that it reduces the current flowing through the circuit rather than increasing it. When current has to arc across a gap, the gap introduces resistance, which limits current flow. A 15-amp circuit with a series arc fault might only be carrying 5 or 8 amps. Your standard breaker is waiting for current to exceed 15 amps before it trips. At 5 amps, the breaker sees nothing wrong. Meanwhile, those 5 amps are arcing across a gap at thousands of degrees, charring the wood framing around the wire.
This is the fundamental problem: a series arc fault produces extreme, fire-starting heat while drawing less current than normal operation. The circuit breaker has no mechanism to detect it. The wiring could be arcing inside your wall for hours -- slowly charring the surrounding materials until they reach ignition temperature -- and the breaker will never trip.
Parallel Arc Faults: When Conductors Cross
A parallel arc fault occurs when electricity arcs between two different conductors -- typically between the hot wire and the neutral wire, or between the hot wire and a grounding conductor. This happens when the insulation separating two conductors breaks down, allowing them to come close enough for electricity to jump the gap.
Parallel arc faults can draw significantly more current than series arcs because the arc creates a low-resistance path between two conductors at different voltages. In some cases, a parallel arc fault will draw enough current to trip a standard breaker. But not always. The arc may be intermittent -- flashing on and off as the gap changes slightly due to thermal expansion or vibration. The breaker sees brief spikes of current followed by normal levels, and the thermal element in the breaker does not heat up enough to trip.
Common causes of parallel arc faults include staples that penetrate both conductors in a cable during installation, physical damage that strips insulation from both wires at the same point, water intrusion that creates a conductive path between conductors, and age-related insulation failure in older wiring systems.
Common Causes of Arc Faults in Homes
Arc faults do not happen randomly. They have identifiable causes, many of which are present in homes throughout Aiken and the surrounding area.
Nails and screws through wiring. This is one of the most common causes of arc faults. When a homeowner hangs a picture, installs a shelf bracket, or mounts a television, the nail or screw can penetrate a wire running through the wall cavity. The damage may not cause an immediate problem. The nail may sit against the wire for months or years, slowly wearing through the insulation from vibration and thermal cycling until the conductor is exposed and arcing begins.
Loose connections. Every wire connection in your home -- at the panel, at outlets, at switches, at junction boxes -- is a potential failure point. Connections that were properly tightened at installation can loosen over time from thermal cycling. A loose connection creates a tiny gap between the wire and the terminal. Current arcs across that gap, generating heat that further deteriorates the connection, creating a larger gap, producing more arcing, in a cycle that escalates until the connection fails completely or a fire starts.
Damaged extension cords and power cords. Extension cords that are pinched under furniture, run under rugs, or stapled to walls can sustain internal conductor damage that leads to arcing. A cord that appears undamaged on the outside may have a partially severed conductor inside that is actively arcing whenever the cord carries load. Frayed or damaged power cords on appliances present the same risk.
Rodent damage. Rats, mice, and squirrels chew on wire insulation, exposing the conductor underneath. This is extremely common in attics and crawl spaces throughout the Aiken area. The exposed conductor can arc to nearby grounding conductors, metal framing, or other exposed wires, and the surrounding nesting material and insulation provide ready fuel for the resulting fire.
Old and deteriorated wiring. The insulation on residential wiring has a finite lifespan. Rubber-insulated and cloth-insulated wiring from the mid-1900s becomes brittle and crumbles with age, exposing bare copper. Even modern thermoplastic insulation degrades over decades, especially in hot environments like attics where summer temperatures can exceed 150 degrees Fahrenheit. As insulation fails, the risk of arcing increases.
Improper DIY wiring. Homeowners who perform their own electrical work sometimes create conditions that lead to arc faults: wire splices made outside of junction boxes, connections made with tape instead of wire nuts, undersized wire stapled tightly enough to damage the insulation, and cables routed through sharp-edged holes in metal framing without bushings.
Why Standard Circuit Breakers Cannot Protect Against Arc Faults
Standard circuit breakers contain two protective mechanisms. A thermal element -- a bimetallic strip that bends when it heats up -- responds to sustained overcurrent by tripping the breaker when current exceeds the rated amperage for more than a few seconds. A magnetic element -- an electromagnet that activates instantly at very high current levels -- responds to short circuits by tripping the breaker in milliseconds.
Both mechanisms respond to current magnitude. The thermal element trips when current is too high for too long. The magnetic element trips when current spikes to extreme levels. Neither mechanism has any ability to analyze the waveform of the current flowing through the circuit. Neither can distinguish between normal current flow and the erratic, intermittent current signature produced by an arc fault.
A series arc fault, as described above, actually reduces current below normal levels. The breaker sees less current than expected and has no reason to trip. A parallel arc fault may spike briefly but often falls back to normal levels before the thermal element heats enough to trip. In both cases, the breaker's inability to analyze the character of the current flow -- only its magnitude -- leaves the home unprotected against the most common cause of electrical fires.
The Scale of the Problem
The NFPA estimates that electrical distribution and lighting equipment causes an average of 34,000 home structure fires per year in the United States, resulting in approximately 470 civilian deaths, 1,100 civilian injuries, and $1.4 billion in direct property damage annually. Arc faults are implicated in a significant percentage of these fires.
The U.S. Consumer Product Safety Commission has identified arcing faults as a leading cause of residential electrical fires and has endorsed the development and adoption of AFCI technology as a means of reducing fire deaths and property losses.
These are not abstract statistics. They represent real homes, real families, and real tragedies. Many of these fires start inside walls where they smolder undetected until they break through into the living space, often while occupants are asleep.
How to Reduce Your Risk
While you cannot see inside your walls to inspect every inch of wiring, there are concrete steps you can take to reduce the risk of arc fault fires in your home.
Install AFCI breakers. Arc Fault Circuit Interrupter breakers contain electronics that analyze the waveform of current on the circuit and detect the distinctive signature of arcing. When arcing is detected, the AFCI breaker trips within milliseconds. AFCI breakers are now required by the NEC in most habitable rooms for new construction, but they can also be retrofitted into existing panels. Adding AFCI breakers to bedroom and living area circuits is the single most effective step you can take to protect against arc fault fires.
Have your wiring inspected. A professional electrical inspection identifies many of the conditions that lead to arc faults: loose connections, deteriorated insulation, rodent damage, and improper wiring. An inspection cannot see inside every wall, but it examines all accessible wiring and tests every outlet for proper connections.
Avoid driving nails and screws into walls near outlets and switches. Electrical wiring runs vertically from outlets and switches to the top or bottom plates of the wall framing. Before driving a nail or screw into a wall, consider whether there might be wiring behind that location. If an outlet or switch is directly above or below your planned fastener location, there is a good chance wiring runs through that area.
Replace damaged cords immediately. Do not use extension cords, power strips, or appliance cords that show any signs of damage: fraying, cracking, exposed wire, or burn marks. Replace them.
Do not run cords under rugs or through walls. Running extension cords under carpet or through wall cavities creates conditions where damage is invisible and heat cannot dissipate.
Address rodent problems. If you have evidence of rodents in your attic, crawl space, or walls, have the infestation addressed and then have an electrician inspect the wiring in those areas for damage.
Protect Your Home
Arc faults are a serious, well-documented fire hazard that exists in every home with electrical wiring. The risk increases with the age of the wiring, the presence of physical damage, and the absence of arc fault protection. Unity Power & Light can assess your home's wiring condition, identify risk factors, and install AFCI breakers to provide the protection that standard breakers cannot. If you live in an older Aiken home and have questions about your electrical safety, we are here to help.