Arc fault circuit interrupters prevent electrical fires caused by damaged or deteriorating wiring. Here’s how they work, where they’re required, and why older homes should have them too.

Most homeowners are familiar with two types of electrical protection: the breaker that trips when a circuit gets overloaded, and the GFCI outlet in the bathroom that cuts power when it detects a ground fault. Both are well understood and easy to explain.

Arc fault circuit interrupters — AFCIs — are less familiar, but they protect against something that neither of those devices can catch. And in many cases, they’re the only thing standing between a hidden wiring problem and a house fire.

What an Arc Fault Actually Is

An arc fault is an unintended electrical discharge that occurs when current jumps across a gap or through damaged insulation. It’s different from a short circuit, where two conductors make direct contact and cause an immediate, obvious fault. Arc faults are subtler. They can happen inside a wall, inside a device, or anywhere along a circuit where wiring has been damaged, pinched, or has simply degraded over time.

The dangerous thing about arc faults is how much heat they generate. An electrical arc can reach temperatures exceeding 10,000 degrees Fahrenheit — hot enough to ignite wood framing, insulation, or other building materials inside your wall long before anything on the surface shows a sign of trouble. By the time smoke is visible, the fire may already be well established inside the wall cavity.

A standard circuit breaker won’t catch this. Breakers respond to overcurrent — too much electricity flowing through the circuit at once. An arc fault can generate enormous heat without ever drawing enough current to trip a breaker. That’s the gap AFCIs are designed to fill.

How AFCI Breakers Work

An AFCI breaker continuously monitors the electrical waveform on a circuit. Normal electrical current has a predictable, consistent pattern. When an arc fault occurs, it produces a distinct signature — a rapid, irregular fluctuation in the current — that the AFCI’s internal electronics are specifically designed to recognize.

When that signature is detected, the breaker trips in milliseconds, cutting power to the circuit before the arc can generate enough sustained heat to start a fire.

Modern AFCI breakers use sophisticated algorithms to distinguish between a genuine arc fault and normal electrical “noise” produced by things like vacuum cleaners, light dimmers, or other devices that create minor fluctuations in the current. Earlier generations of AFCIs were prone to nuisance tripping — cutting power when nothing was actually wrong. Current technology has largely solved that problem.

Where AFCIs Are Required

The National Electrical Code has expanded AFCI requirements steadily over the past two decades, and Tennessee follows the NEC as its baseline electrical standard. Today, AFCIs are required in virtually all living spaces in new residential construction — bedrooms, living rooms, dining rooms, hallways, closets, and most other areas of the home.

This wasn’t always the case. Early NEC requirements only covered bedrooms. Each subsequent code cycle added more locations until the current standard essentially requires AFCI protection throughout the living space of any newly built home.

What this means practically: if your home was built or substantially renovated in the last several years, AFCI breakers are likely already in your panel. If your home is older, they almost certainly aren’t — and your wiring may have had decades to develop exactly the kind of wear and deterioration that AFCIs are designed to catch.

AFCIs vs. GFCIs: Understanding the Difference

These two devices are frequently confused, and they do sound similar. Here’s the straightforward distinction:

A GFCI (Ground Fault Circuit Interrupter) protects people. It detects current leaking outside the intended circuit path — the kind of fault that can send electricity through a person who is in contact with water or a grounded surface. GFCIs are required in wet areas: bathrooms, kitchens, garages, outdoors, and anywhere water and electricity might intersect.

An AFCI protects the structure. It detects the electrical signature of an arc — the kind of fault that can ignite building materials inside walls and ceilings. AFCIs are required in living spaces where wiring runs through or adjacent to combustible materials.

Both protect against real hazards. They just protect against different ones, and neither one substitutes for the other. Some installations call for both — there are combination AFCI/GFCI breakers available for circuits that need protection against both types of faults.

Why Older Homes Need a Closer Look

The electrical code only requires AFCIs in new construction and permitted renovations. If your home was built before these requirements applied to your area, there’s no mandate to retrofit — but there’s a compelling reason to consider it anyway.

Older wiring is more likely to have developed the conditions that cause arc faults. Insulation becomes brittle and cracks. Connections loosen over time. Wiring that was nailed through during construction may have damaged spots that have been sitting inside walls for decades. Homes that have had multiple owners, multiple renovations, or any previous DIY electrical work are particularly worth scrutinizing.

Adding AFCI breakers to an older home’s panel is one of the more cost-effective electrical upgrades available. The breakers themselves replace standard breakers in your existing panel and require no changes to the wiring in the walls. A licensed electrician can assess which circuits would benefit most and install them in a single visit in most cases.

Signs Your Home Might Have an Arc Fault Problem

AFCIs are designed to catch problems before they become fires, but there are sometimes warning signs worth paying attention to:

• Lights that flicker intermittently with no obvious cause
• Outlets or switches that feel warm or show discoloration
• A burning smell near outlets, switch plates, or your panel
• Breakers that trip without an obvious overload
• Any history of rodents in the home (rodents frequently damage wiring insulation)
• Wiring that has been stapled, nailed through, or run through tight spaces during past renovations

None of these are guaranteed indicators of an arc fault, but all of them are worth having a licensed electrician evaluate — with or without AFCIs already installed.

What to Expect During Installation

Installing AFCI breakers is a panel-level job. Your electrician will open the panel, remove the existing standard breakers on the circuits being upgraded, and replace them with AFCI breakers of the same amperage rating. AFCI breakers have a neutral wire connection that standard breakers don’t require, so the installation is slightly more involved than a simple breaker swap — but it’s still a straightforward job for a licensed professional.

After installation, your electrician should test each circuit to verify the breakers are functioning correctly and not producing nuisance trips on your specific wiring.

The Bottom Line

Arc faults are responsible for an estimated 30,000 home fires in the United States every year, according to the U.S. Consumer Product Safety Commission. They’re one of the leading causes of residential electrical fires precisely because they’re invisible — burning inside walls and ceilings with no warning until the damage is already serious.

AFCIs exist specifically to catch what standard breakers miss. If your home doesn’t have them, it’s worth a conversation with a licensed electrician about where they make the most sense to add.

AC/DC Electrical Services works with homeowners across Middle Tennessee and North Alabama on exactly these kinds of upgrades. If you’re not sure whether your home has AFCI protection or whether your panel is up to current standards, we’re happy to take a look.