How Arc Fault Breakers (AFCI) Work?

afci

Home protection and safety are some of the most important aspects for any homeowner, as this can literally save both your home and the lives of your loved ones.

Electricity and electrical devices can be as dangerous as they are useful. When it comes to fire hazards, many advances have been made in electrical safety in recent years. To protect against electrical fires, the NEC added arc fault circuit interrupters into the electrical code in 1999 and has expanded their uses in recent years.

How do arc fault breakers work? Arc Fault Breakers work by monitoring the electrical circuit for signs of electrical arcs faults. When the arc fault breaker registers an arc fault, it immediately breaks the circuit cutting power to prevent electrical fires.

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Having a better understanding of how electrical arcs happen and what they are is the first step in knowing how AFCI circuits work and how they prevent any hazardous situations from starting in the first place.

So, let’s take a look at how arc fault circuits work.

How Do Arc Fault Breakers Protect Your Home?

An arc fault breaker (or AFCI, short for Arc Fault Circuit Interrupter) is a device that protects our homes by preventing arc faults from happening as they can be incredibly dangerous and hazardous.

Following the data from the National Fire Protection Association from 2011, over 47,700 home fires were reported to have started due to electrical malfunctions. The estimations provided by the Consumer Product Safety Commission indicate that more than 50% of the electrical fires can be avoided by using an Arc-fault circuit interrupter (or AFCIs).

The numbers are definitely in favor of the AFCIs but before we get into that, let’s take a look at what exactly is an arc fault as frequently this is the main culprit of an electrical fire.

What Is an Arc Fault?

An arc fault is a spark that can happen between two conductors or wiring connections.

For example, this can occur when the conductors (or wires) have damaged, frayed or worn insulation. When the insulation is compromised in some way, electricity can escape using the air like a conductor to travel between two places – and this jump between two conductors with the help of the air is called an (electrical) arc fault.

Have you ever heard hissing or popping noises coming out of your outlets?

This can be a good sign of a possible tiny electrical arc happening every time you use your outlet. It should be addressed immediately as electrical arc faults are very hazardous. If that happens, make sure to have a certified electrician check the outlet and replace it if needed.

This hissing or popping is sometimes referenced as a “backstab” wire connection – or in other words, it is a loose wiring connection that can create arc faults.

What Makes Electrical Arc Faults Dangerous?

Arc faults are very dangerous as they generate heat.

When the electrical current travels through the air, it converts some of its energy into heat that can reach incredibly high temperatures – exceeding 10,000 F.

As a comparison, the temperature at the surface of the Sun is about 10,000 F, too.

This high temperature can melt and ignite anything that is in close contact.

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Using the example above, if you unscrew the hissing outlet, you might see signs of arcing like burning areas on the plastic or the wiring.

The damage to the outlet and old wiring is basically a fire waiting to happen, and this is how a lot of electrical fires start.

This is why having proper protection with an arc fault breaker is vital to our homes' safety as it will cut out the electricity before reaching such high temperatures and causing damage.

How Does an Arc-Fault Circuit Interrupter Work?

afci diagram

AFCIs work by “listening” to the power line for any signs of an arcing happening.

The arc fault breaker contains an electronic sensor that detects electrical arcs, usually around 100 kHz, sustained for more than a few milliseconds.

combination AFCI breaker provides protection against overload protection and short circuit protection caused by:

  • parallel arcing (line to neutral)
  • series arcing (a loose, broken, or otherwise high resistance segment in a single line)
  • ground arcing (from the line, or neutral, to ground)

When an arc fault breaker or a combination arc fault breaker detects a potentially dangerous arc fault, it will immediately shut down the electrical current flowing through a circuit if and when it detects an electrical arc.

There can be intended electrical arcs that happen naturally with the regular daily use of switches, electrical tools equipped with brushed motors, plugs, and there can be unintended electrical arcs that are dangerous. Usually, the newer AFCIs can distinguish between the two and know when to act accordingly.

The way AFCI work can also depend on their type, as we have seen a few types of AFCI breakers come out throughout the years.

AFCI receptacles, like AFCI breakers, contain electronic components that monitor the circuit for a dangerous electrical arc on the circuit. The AFCI receptacle is installed on the first outlet of the branch circuit and protects all the receptacles downstream on that branch circuit.

Unlike AFCI breakers, you may use AFCI receptacles on any wiring system regardless of the electrical panel.

What Are the Different Types of AFCI?

Ever since the NEC first required AFCIs, they have been evolving to provide better home protection, work more efficiently, and incorporate new features.

A few different types of AFCI can be found in the different homes depending on when they were built and if they have been renovated.

1. Branch Feeder Type AFCI Breakers

The branch feeder type is the oldest representative for the AFCI breakers.

These provide moderate protection as they can detect only parallel with the load arcs like:

  • line-to-ground
  • line-to-neutral.

The NEC first required them in 1999, and, from 2008, they were phased out and are no longer in use as the combination type AFCIs have effectively replaced them.

2. Combination AFCI Breakers

A combination AFCI breaker does not mean it offers GFCI protection.

The word combination here means that unlike the branch feeder type, the combination AFCI breaker can detect and protect against both parallel arcing and series arcing. This is an electrical arc created along the same conductor or wire.

This means that Combination AFCI can detect and protect from all three kinds of arcing:

  • parallel arcing (line to neutral)
  • series arcing (a loose, broken, or otherwise high resistance segment in a single line)
  • ground arcing (from the line, or neutral, to ground)

Series arcing means that the electrical arc continues along the same conductor or wire, but it makes an arc somewhere along the line. While the parallel arcing is when the electricity is escaping one conductor and continues its path using a different conductor.

The combination type of AFCI breakers can be considered the most widely used ones as they provide a convenient way to protect your home. An AFCI breaker will allow for the installation of GFCI outlets down the line.

3. Dual-Function Circuit Breakers

They protect against both arc faults and ground faults – effectively combining the functions of AFCI with a GFCI.

The electrical code has been continuously changing, and the requirements have been increasing with each of its revisions. It was only a question of time before we had these introduced, and they will most probably be the ones that will be used in the construction of the new dwelling units in the future.

Since they are a mixture between the combination AFCI breakers and a GFCI breaker, they provide the best protection possible for both us and our homes and are a great way to save money and time.

4. AFCI Outlets

afci outlet

AFCI outlets can be found frequently in some older homes.

AFCI receptacles do offer arc fault protection. As mentioned above, the AFCI receptacle protects that receptacle and any receptacles downstream from the receptacle. The AFCI receptacle must be installed on the load circuit.

This can be tricky in older houses as some circuits will serve multiple rooms.

Another difference is that AFCI breakers will often cut power to the entire room, including lights. AFCI receptacles may not do this if the lights are not on the same circuit or are not downstream from the AFCI receptacle.

For a combination type AFCI breaker to work properly, the circuit neutrals need to be separated. This might not be the case with older dwelling places, in which case a combination type of an AFCI receptacle is the better option.

What Are the Common Causes for an Arc Faults?

Knowing the most frequent reasons for an arc fault is the first step in making our home a safer place to live in. An arc fault can be caused by:

  • Damaged or worn wire insulation.
  • Loosely connected wires.
  • Static electricity.
  • Arc faults in electrical circuits in close proximity.
  • Faulty tools and electrical appliances.
  • Worn, dirty, and poorly maintained circuit breakers.
  • Liquids near electrical tools.
  • Exposed live parts, and more.

An arc fault can happen in many different ways. For example, a screw or a nail behind the wall can damage the wire's insulation. This is why AFCIs are vital as they will protect our homes from potential hazardous effects.

When any of these happen, a properly working AFCI will immediately trip and protect you and your home by instantly shutting down the power.

However, AFCIs can sometimes trip without an apparent reason. At one point in time, this used to be a frequent issue for many homeowners and electricians, as well – this is something known as nuisance tripping.

What Is Nuisance Tripping, and Why Does It Matter?

Nuisance tripping (also known as ghost tripping) used to be a big problem with AFCIs – this is when the breaker constantly or frequently trips without an obvious reason.

What can cause nuisance tripping:

  • Bad wiring practices or improper wiring.
  • Incompatible electrical devices
  • Faulty electrical devices.
  • Old AFCIs

If your AFCIs keep tripping without reason, this should be immediately addressed and inspected as this is a potentially dangerous situation that should never be ignored.

Nowadays, AFCIs are better at detecting the unintentional arc (that is dangerous) and intentional ones created by some devices and machinery (like some power tools with brushed motors). In addition to that, today's electrical equipment is better at not creating such fluctuations that would cause an AFCI to trip.

If you think you may need an electrical panel upgrade, our article Signs Your Electric Panel Needs an Upgrade: Safety & Costs to Replace may help.

How to Test if an Afci is Working Properly

The AFCI breakers should be tested every month to ensure that they are working correctly and providing adequate protection to our homes.

This is done in just a few steps:

  • Carry out the test while the power is on. Make sure to unplug any devices plugged in the electrical circuit to avoid any potential damage during a test. Especially make sure that any computers, laptops, and mobile phones are disconnected.
  • Go to the electrical panel.
  • While the breaker is in the ON position, press the Test button.
  • Pressing the Test button will cause the breaker to trip. It should go to either the Trip position or the OFF position.
  • If the breaker trips when the button is pressed, this means it is working properly. For the sake of the test, you can try to plug in a table lamp to check if there is electricity flowing in the circuit.
  • You can switch it back to ON now.

Using the Test button is the best way to test an AFCI breaker. If it doesn’t trip, this means that the breaker has gone bad and needs to be changed as soon as possible by a certified electrician.

There are various AFCI testers and indicators that some people might use. Still, the manufacturers are usually not recommended and do not always work on all brands of breakers.

Where Are AFCIs Required?

With every code revision after AFCIs were first introduced back in 1999, the requirements have been steadily increasing, covering more and more rooms and areas of the dwelling properties.

First, they were to be installed in bedrooms and were meant to protect against electrical blanket fires, but that has changed ever since then.

Eventually, they were used for detecting loose wire connections to the receptacles.

According to the NEC, appropriate arc fault protection needs to be installed in any room with 120 volts, 15 to 20 amp circuits.

Arc fault protection is usually not required in bathrooms, garages, and outdoor or external areas. Keep in mind, though, that at the same time, these all need to have GFCI protection installed.

AFCI protection needs to be installed in:

  • Kitchens.
  • Dining rooms.
  • Family rooms.
  • Libraries.
  • Dens.
  • Bedrooms.
  • Closets.
  • Laundry areas.
  • Parlors.
  • Sunrooms, and more.

The Difference Between Arc Fault, Short Circuit, and Ground Fault

The terminology can get really confusing. Especially for the people that are not that tech-savvy, terms like – ground fault, arc fault, short circuit, and more – can sound very intimidating.

However, these three are the most common terms that can be easily mixed up sometimes as they may seem like the same thing, yet, they are not.

They are not interchangeable and should be differentiated; they pose a different kind of hazard and are caused differently. Because of that, they require different safety measures to be taken to provide your home with adequate protection.

Let’s take a look:

1. Short Circuit

A short circuit is when the current goes through an unintended path with very low or no electrical impedance.

For example, the standard short circuit term refers to when the wire carrying the electrical current comes into contact with a neutral wire. Since the two wires are intended for different voltages, there is a low resistance, and a large amount of electrical current is being transferred through that connection.

This is very dangerous as this can cause sparks, flames, and more.

2. Arc Fault

An arc fault can be considered a type of short circuit. When you have a loose connection or corroded wires, an electrical arc can generate high amounts of heat.

An arc fault usually will not be detected by a GFCI or the circuit breakers, leaving your home vulnerable.

3. Ground Fault

A ground fault can be considered a type of short circuit, too. In this instance, the electrical current comes into contact with a grounded object. This can be anything that will allow the electricity to travel to the earth as short of a distance as possible, even a human body.

This is why ground faults are so dangerous as they can lead to fatal consequences.

Can a GFCI Substitute an AFCI?

A standard AFCI is not designed to protect against ground faults, and GFCIs are not designed to protect against arc faults.

It is vital to follow the NEC requirements to have proper protection for your home. The NEC would require both GFCI and AFCI protection in some cases.

This is usually done by installing a combination AFCI breaker and then having GFCI equipped receptacles installed down the circuit.

A GFCI cannot substitute an AFCI or vice versa, but they can be combined.

The dual function AFCI breakers that we went through earlier in this article are the ones that can offer the best possible protection from ground faults and arc faults.

Normally, AFCIs and GFCIs are not interchangeable; however, with time, a new type of receptacles and breakers have been introduced that offer GFCI and AFCI protection at the same time.

Dual function outlets can save us some money and time as that way we don’t need to worry about the complex installations of breakers and outlets. At the same time, they still provide us with much-needed protection against both electrical fires and ground faults.

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Hubert Miles

I've been conducting home inspections for 17 years. I'm a licensed Home Inspector, Certified Master Inspector (CMI), and FHA 203k Consultant. I started HomeInspectionInsider.com to help people better understand the home inspection process and answer questions about homeownership and home maintenance.

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