Arc fault protection: Separating fact from fiction

To help prevent arcing electrical fires, arc-fault circuit-interrupter (AFCI) technology detects hazardous conditions, cutting off power to the circuit. Unfortunately, myths abound.
Photo © BigStockPhoto

by Jonathan Lam

According to research from the National Fire Protection Association (NFPA), there was an average of 45,210 home structure fires caused by electrical failure or malfunction between 2010 and 2014. Of those, 57 percent involved electrical distribution, lighting equipment, or power transfer. Although the annual occurrence of fires is declining each year, electrical fires are still one of the leading causes of residential building blazes. Caused by dangerous arcing from defective or worn insulation, faulty contact, and operating equipment, these fires can be both costly and deadly.

To help prevent arcing electrical fires, arc-fault circuit-interrupter (AFCI) technology was introduced in 1999. AFCIs are designed to detect hazardous arc-fault conditions and cut off power to the circuit before it can start a fire. With the 2017 edition of the National Electric Code (NEC), arc-fault protection is required on all 120V, single-phase, 15- and 20-amp branch circuits supplying outlets or devices in all dwelling areas, laundry areas, and kitchens of new residential construction, including mid-rises, multifamily high-rises, and university/college dormitories.

Although NEC began requiring AFCI protection nearly 20 years ago, the technology’s application is still largely misunderstood. This has led to numerous, potentially dangerous myths about arc faults and their circuit breakers.

Myth: AFCI devices only detect problems with the appliances plugged into them
AFCI technology uses advanced electronics to sense different arcing conditions. It detects and protects against a full range of issues that may arise, including damaged wiring, overheated or stressed electrical cords, worn electrical insulation, and faulty connected equipment. An AFCI device protects the entire circuit from the electrical panel through the downstream wire to the outlet, along with all appliances and equipment plugged into that circuit.

Myth: AFCI devices are prone to nuisance tripping
If an AFCI device trips, it is most likely the result of a potentially dangerous arcing condition detected by the device. Other reasons why an AFCI device may trip include a fault to ground, thermal overload, or short circuit. For example, plugging in too many cord-connected appliances in a single outlet can cause an overload, or a neutral touching the ground can cause the circuit breaker to trip. In some cases, the breaker may trip due to damaged or faulty lighting fixtures or appliances.

Arc fault detection is accomplished by using advanced electronic technology to monitor the circuit for the presence of ‘normal’ and ‘dangerous’ arcing conditions. Some equipment in the home, such as a motor-driven vacuum cleaner or furnace motor, naturally creates arcs. This is a normal arcing condition. Another normal arcing condition occurs when a light switch is turned off and the opening of the contacts creates an arc.

A dangerous arc occurs for many reasons, including damage of the electrical conductor insulation. When arcing occurs, the AFCI analyzes the characteristics of the event and determines if it is a hazard. AFCI manufacturers test for hundreds of possible operating conditions and then program their devices to monitor constantly for the normal and dangerous arcing conditions.

Myth: Standard circuit breakers provide adequate protection against arc faults
Standard thermal magnetic circuit breakers provide protection against short circuits and overloads, but offer no defense against dangerous arc fault conditions. An AFCI is designed to detect a wide range of arcing electrical faults to help reduce the risk of an electrical system being an ignition source of a fire. Standard thermal magnetic circuit breakers do not detect low-level hazardous arcing currents that have the potential to initiate electrical fires, which can be a silent killer because they can occur in areas of the home that are hidden from view and early detection. AFCI technology is built to protect the circuit in a manner that will reduce its chances of being a source of an electrical fire.

Myth: Outlet-branch AFCI receptacles are just as effective as arc fault circuit breakers
There are only six approved ways to provide AFCI protection on a circuit, per NEC section 210.12. Of those, only two allow for outlet branch circuit (OBC) AFCI receptacles to be used on a home-run circuit in new construction. However, NEC requires additional insulation in the form of metal-enclosed wiring or wiring in conduit encased in 50 mm (2 in.) of concrete. This is because OBC AFCI receptacles cannot protect the home run against parallel arcing faults in all cases. This leaves almost 30 percent of every new home at risk should a parallel arcing fault condition occur.

AFCI circuit breakers, on the other hand, protect the entire circuit—including the home run—from both parallel and series arcing faults. They meet all stringent Underwriters Laboratories (UL) requirements.

Conclusion
While hard to believe, there are still some who think arc fault itself is a myth made up by manufacturers to sell more devices. This is not only untrue, but it is also a dangerous misconception that can put lives at risk. NEC and other standardizing bodies agree arc fault is a real danger, and arc fault circuit breakers offer the best protection against dangerous arcing conditions. Despite this, some builders, organizations, and even legislation question the need for AFCI protection. The bigger question is if the technology exists to prevent arcing events and damaging electrical fires, why would you not use it?

Jonathan Lam is the residential business development specialist for Square D by Schneider Electric. He is responsible for leading initiatives that help develop and support relationship with electrical contractor and channel partners related to residential products. With a background in mechanical and systems engineering, Lam has served roles in product design, verification, testing, and management.

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One comment on “Arc fault protection: Separating fact from fiction”

  1. You expect us to consider your article as unbiased and factual but you can’t even pick the correct style plug from the variety of stock photos you have to choose from.

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