Arc Fault Circuit Interrupters

Why AFCI's are Important

Dear Mr. Electrician: What is the reason for Arc Fault Circuit Interrupters or AFCI?

Answer: Arc Fault Circuit Interrupters provide an additional level of protection against fires.  Electrical arcs create heat and sparks.  If combustible materials are nearby, a fire could erupt.  Arc Fault Circuit Interrupter circuit breakers protect us from potential fire starters that we cannot see.  NOTE: Some text links below go to applicable products on Amazon.   As an Amazon Associate I earn from qualifying purchases.

Many residential homes have wood frame construction.  The electrical switch and receptacle boxes in the walls are attached to wood framing members.  The electrical wiring runs through the wood framing.  Wood is a combustible material.  If heat and sparks develop inside the wall you would not know it until it becomes obvious.

An early warning indicator for possible loose connections is blinking or flickering lights.  If you see lights flickering fairly regularly, you may have a loose connection somewhere or something else is going wrong.  Have a professional electrician look into it for you.

A Series Arc or low current arc can be as a result of frayed power cords, old appliances, or loose electrical connections.

A Parallel Arc or high current arc can occur from a screw or nail being partially driven into a live wire causing a poor connection to be made between two current carrying conductors.  Also known as a line-to-neutral arc.

Line-To Ground Arc or ground fault indicates electrical current leaking to earth ground.

A combination AFCI will protect against the three types of arcs.

Two single pole 20 amp Cutler Hammer Type CH Arc Fault Circuit Interrupter circuit breakers in a load center
Two single pole 20 amp Cutler Hammer Type CH Arc Fault Circuit Interrupter circuit breakers in a load center


An electrical arc can be caused by lightning of course and your grounding electrode system, if it is in good condition, should handle that.

However other causes of arcing are usually not as obvious until some damage or a fire takes place.  For instance, an electrical receptacle with a loose connection may be fine until one winter you decide to plug a high wattage portable electric heater into it.

The heater uses a lot of current to keep you warm.  With the extra LOAD on the electrical circuit, the loose connection that was fine for a few years now arcs each time the heater is on.

Burned wire on an electrical outlet
A burned wire on an electrical outlet

I found the above electrical outlet inside of a kitchen cabinet for the over-the-range microwave oven.  It was obviously not installed by someone qualified.  In addition to the loose connection that caused the arcing and subsequent burning, there was no connector in the back of the box to protect the cable from the edges of the metal electrical box.  In fact the knockout was punched out, but is still attached to the box.

The electrical box was also not grounded properly.  There should have been a ground wire connection directly attached to the metal box.  Instead the ground wire only connects to the electrical outlet.  Something else that was a code violation, the electrical box was not screwed to the cabinet, it was just floating.

An AFCI circuit breaker would have tripped off long before the damage got this far.

Click here to read my blog post about properly grounding outlets and switches.

Arcing creates heat and sparks which can cause damage to the electrical receptacle, the wiring in the electrical box and wall, and even the heater plug.  In addition, the potential for fire is high.  If combustible materials are nearby such as drapes and curtains, bedding or even furniture, a fire can start whether you are home or not.


– Loose or broken plugs or cords on appliances and lamps.
– Nicks in the house wires and/or the wire insulation that occurred during the original construction or a renovation thereafter.  Even a nail driven into the wall to hang a painting can nick a wire.
– Worn out electrical receptacles that do not hold the plugs in tightly.
– Frayed insulation on appliances and lamps.
– Worn electrical switches.
– Very old electrically powered tools and appliances where the internal electrical insulation has degraded.

Burned wires on an electrical outlet without AFCI protection
Burned wires on an electrical outlet without AFCI protection

In the photo above the homeowner had replaced the existing electrical receptacle himself for an outlet with a different color.  Not being a professional electrician he was unaware of the torqueing requirements for the screw terminals.  He also put the ground wire backwards on the green screw.  The hook on the wire should close as the screw tightens in the clockwise direction.

With that much heat sometimes the plastic electrical boxes get damaged and must also be replaced.

Another possibility for wiring getting damaged is from a major redecoration or renovation project where the old existing wiring is disturbed.  A small unnoticed problem that occurred during the original renovation may not manifest itself into a major hazard until months or years later.  Existing wiring is best left alone in older houses.

Like everything else in a house, wiring ages whether you use it or not.  However this does not mean that you should replace every wire in your house after so many years.  The wiring should last the life of the house as long as it is not disturbed and minor maintenance such as tightening connections is performed every few years.

Maintenance such as tightening all connections in the circuit breaker panel and at all switches and receptacles will help to prevent arcing and heat.  It is required that you torque all electrical connections according to factory specifications.  A torque screwdriver is used for that purpose.

All wiring devices and electrical equipment are accompanied by installation instructions or labeling that mention the torqueing requirements.  Torqueing is done with a torque wrench or a torque screwdriver depending on the device or equipment.

Pigtailing electrical receptacle outlets is better than feeding through each outlet in terms of reducing arcing.  When a receptacle outlet is pigtailed the full load of the circuit is not being carried through the receptacle, only the LOAD for that receptacle.

Some manufacturers of AFCI circuit breakers have built-in diagnostic codes to help figure out why a circuit breaker tripped.


Some manufacturers of AFCI circuit breakers have built-in diagnostic codes to help figure out why a AFCI circuit breaker tripped.

On Siemens one pole AFCI circuit breakers if LEDs A and B trip indicators are both off it was an overcurrent condition that caused the breaker to trip.  With LED A on and LED B off it was an arc fault.  If both LED A and B are on after the Siemens one pole AFCI trips, that indicates an arc fault to ground.

Siemens two pole AFCI trip indicators are slightly different.  Three yellow lights off indicate an overcurrent condition.  Yellow light 1 on indicates an arc fault on phase A.  Yellow light 3 on indicates an arc fault on phase B.  All three yellow lights on are for an arc fault to ground.

Cutler Hammer Type CH AFCI circuit breakers (Tan handle) have blinking lights to indicate the cause of the circuit breaker trip.  1 blink indicates a series arc.  Two blinks are for a parallel arc.  3 blinks indicate a short delay.  4 blinks are for overvoltage.  5 blinks indicate a ground fault.  6 blinks means a self-test failure and the AFCI breaker should be replaced.  No blinking lights after the breaker has tripped means an overload or a short circuit.

Eaton Type BR AFCI circuit breakers also has a blinking light to indicate the type of condition that caused it to trip.  No blinking light is an overload or short circuit.  1 blink is a low current arc.  2 blinks is a high current arc.  3 blinks means a short delay.  4 blinks is for overvoltage.  6 blinks indicates a self-test failure and the breaker should be replaced.

Square D AFCI trip indication is a little different.  On Type QO and Type Homeline AFCI circuit breakers after a breaker trips, push the Test button and turn the breaker back on at the same time.  If the breaker trips immediately after that it means a fault to earth ground.  If the breaker trips again after a 2 second delay, that indicates a parallel or series arc fault.  If the AFCI breaker trips after 5 seconds it means there is a thermal overload or a short circuit.

For more reading on AFCI’s and arc faults in general, Schneider Electric has a downloadable paper explaining it all.

Articles 210.12, 440.65, 550.25, and 406.4(D)(4) in the National Electrical Code pertain to the requirements for arc fault protection.  Replacement electrical receptacles in existing homes must be tamper resistant arc fault receptacles.

Dual Function Circuit Breakers and receptacles are available.  One dual function circuit breaker or receptacle is capable of providing arc fault protection and ground fault protection.

Homes with original aluminum wiring that was installed in the 1970’s should have already had steps taken to its wiring to prevent the excessive arcing that the old aluminum is known for.  See my post on preventative measures for aluminum wiring by clicking here.