Applying and Using Arc-Fault Circuit Interrupters

Applying and Using Arc-Fault Circuit Interrupters

According to the National Fire Protection Association and the National Fire Incident Reporting System data, the five-year period from 1994 to 1998 averaged 73,500 annual electrical fires that were responsible for 591 deaths, 2,247 injuries, and property damage totaling $1,047,900,000. A report by the National Association of State Fire Marshals (NASFM) states that of these 73,500 electrical fires,

According to the National Fire Protection Association and the National Fire Incident Reporting System data, the five-year period from 1994 to 1998 averaged 73,500 annual electrical fires that were responsible for 591 deaths, 2,247 injuries, and property damage totaling $1,047,900,000. A report by the National Association of State Fire Marshals (NASFM) states that of these 73,500 electrical fires, 60,900 or 82% were caused by arcing, not overloads or short circuits.

It may not be realistic to expect arc-fault circuit interrupters (AFCIs) to eliminate all of the conditions that cause arcing fires, but the NASFM report doesn't propse that. However, the report's conclusion does strengthen the case that the frequency of arc-related fires is a cause for further attention and action.

AFCIs were developed to detect and de-energize unwanted electrical arcs on electrical circuits that are likely to cause fires. Unwanted, hazardous electrical arcs occur when live conductors become exposed and the current flows in an arc through air or tracks across an organic material through an unintended path.

A distinction must be made between wanted and unwanted arcs to clarify that a number of arcs inside electrical equipment are normal for the equipment's operation and aren't the cause of unwanted opening of the circuit. For example, many motors are equipped with “brushes” that generate arcs as the motor turns. Temperature regulation is often done by means of contacts that separate and draw an arc like in household irons and cooking appliances. Many appliances have momentary arcs or signals that have some of the electrical characteristics of arcs that are a normal component of the circuit. It's this second function of an AFCI that's so important. After detecting an arc, an AFCI must be able to distinguish between typical circuit characteristics and unwanted hazardous arcs.

AFCIs and the Code. Per 210.12 of the 2002 NEC, “All branch circuits that supply 125-volt, single-phase, 15- and 20- ampere outlets installed in dwelling unit bedrooms shall be protected by an AFCI listed to provide protection of the entire branch circuit.” This includes outlets for receptacles, lights, fans, and smoke detectors in circuits that supply bedrooms.

The Code requirement is concise, but because of the technology's newness, some clarification of applications may be useful.

Art. 100 defines a dwelling unit as: “One or more rooms for the use of one or more persons as a housekeeping unit with space for eating, living, and sleeping, and permanent provisions for cooking and sanitation.” This definition clearly covers most houses and apartments. However, whether it applies to dormitories or hotel rooms is up for interpretation, so it's up to the authority having jurisdiction (AHJ) to make the distinction. If the AHJ considers these units dwelling units, they too must adhere to the requirements of 210.12. Whether bedroom closets are part of the bedroom is also a judgment call for the AHJ to make.

Questions have arisen regarding whether alarm and smoke detector circuits must be AFCI-protected. In some cases, they fall under the category of bedroom outlets. Recall that the purpose of the AFCI is to address the causes of fires. If the potential fire cause is in the smoke detector wiring, the first approach for protection against fire should be to clear the potential cause. During deliberations for revisions for the 2005 NEC, Code-Making Panel 2 confirmed that alarm and smoke detector circuits are intended to be protected if installed on the bedroom branch circuit.

CMP-2 reviewed more than 60 proposals and 80 public comments related to AFCIs for revisions to the 2005 NEC. The wording of 210.12(B) is set to be revised to read as follows:

“Dwelling Unit Bedrooms. All 120-volt, single phase, 15- and 20-ampere branch circuits supplying outlets installed in dwelling unit bedrooms shall be protected by a listed arc-fault circuit interrupter, combination type, installed to provide protection of the branch circuit. Branch/feeder arc-fault circuit interrupters shall be permitted to be used to meet the requirements of 210.12(B) until January 1, 2008.

“FPN: For information on types of arc-fault circuit interrupters, see UL 1699-1999, Standard for Arc-Fault Circuit Interrupters.

“Exception: The location of the arc-fault circuit interrupter shall be permitted to be at other than the origination of the branch circuit in compliance with (1) and (2).

“(1)The arc-fault circuit interrupter installed within 1.8 m (6 ft) of the branch circuit overcurrent device as measured along the branch circuit conductors.

“(2) The circuit conductors between the branch circuit overcurrent device and the arc-fault circuit interrupter shall be installed in a metal raceway of a cable with a metallic sheath.”

The major revision to 210.12 is the specification of “combination” type devices. UL 1699 Standard for Arc-Fault Circuit Interrupters describes multiple types of AFCIs, most notably the “branch/feeder,” “combination,” and “outlet circuit” types.

The branch/feeder is the only type commercially available today. It's the circuit breaker type, which is intended primarily for protection of fixed wiring but also provides some protection of appliance and extension wiring. It's required to detect line-to-neutral arcing at 75A and above and line-to ground arcing at 5A and above.

The outlet circuit type is intended primarily for protection of extension and appliance wiring connected to a receptacle outlet. It's required to detect line-to-neutral, line-to ground, and series arcing at 5A and above.

The combination type combines the performance of the other two types into a single device intended to protect both the fixed and the extension and appliance wiring of the circuit. It's required to detect line-to-neutral, line-to ground, and series arcing at 5A and greater. Several manufacturers have listed products as combination type, but none are commercially available today. However, the combination type is the one that CMP-2 members have desired all along because of its full performance to provide protection to the entire circuit. The panel has given manufacturers until January 2008 to make these generally available, while still allowing for the continued installation of currently available branch/feeder devices until that date.

All currently available AFCIs will detect line-to-ground arcs at 50mA or above even though the Code requirement is 5A and above.

Although CMP-2 has approved these revisions for the 2005 NEC by ballot, the remaining step of approval at the NFPA Annual Meeting in May is still to be completed.

Installing and using AFCIs. You don't need special equipment or testers to install AFCIs. In fact, the installation of a circuit breaker AFCI is similar to that of a GFCI. AFCIs are also well-suited for retrofit applications in older dwellings, including those with 2-wire circuits without a grounding conductor.

A branch/feeder AFCI (circuit breaker type) is designed to fit into existing panelboards and loadcenters that accept circuit breakers of the same type. It can detect a low-level short circuit of 75A or greater that wouldn't be detected by an overcurrent protective device. It also provides detection of an arcing ground fault of 5A or more. This protection is as valid in 2-wire circuits as in 3-wire circuits that include the grounding conductor. The difference is that with the added grounding conductor in the 3-wire circuit, an arc of any level may reach the grounding conductor and be detected at levels below 75A, which provides a degree of protection not available in 2-wire circuits.

If wiring is installed competently, there should be no reason for any testing that wouldn't be conducted on a circuit without an AFCI. However, the following two possible practices can be used to test the installation if a test is desired.

  1. It's possible to verify that the AFCI is functioning properly by using the test button on the device after the installation has been energized. Then leave the AFCI in the energized circuit for some period of time. If it doesn't trip, that's an indication that the circuit is acceptable.

  2. As with any installation, an insulation resistance test can be conducted to verify that the wiring and connections are properly insulated. With this test, high voltages are applied to the circuit. Be sure to keep personnel away from circuits under test and follow safety practices described in NFPA 70E, Articles 120 and 130.

To perform an insulation resistance test, disconnect all loads and verify that unconnected wire ends are insulated. Disconnect the load wire to any AFCI or GFCI in the circuit because these devices may be damaged by high voltage. Use an insulation resistance tester that will apply a direct current voltage of at least 500V to the circuit under test. All resistance readings should be at least 1 megohm (1,000,000 ohms). A successful test will indicate that the insulation is intact and that initiation of an arc would be highly unlikely for the portion of the circuit tested.

Recognize that neither of these tests will identify loose connections. Good workmanship is required as always.

It's also important to note that in the past year, several commercially available AFCI testers have come on the market. These testers operate in various ways. Some provide a low-energy signal intended to simulate a characteristic of an arc. Others may provide a momentary ground leakage intended to operate the line-to-ground detection capability of the AFCI. Although these testers may be useful for some circuit checks, they may not necessarily match the signal detection processor of the AFCI and therefore may not correctly indicate proper operation of the AFCI under test.

Locating an arcing fault. So what do you do if the device trips? How do you best locate the cause of an AFCI trip? There's no single correct answer regarding how to proceed. Just remember that the AFCI will trip from an overcurrent or from an arcing occurrence, which includes a ground fault.

Most nuisance tripping on newly installed AFCIs is caused by one of the following common wiring problems:

  • Neutral conductors grounded on the load side of the AFCI
  • Neutrals of several circuits mixed, crossed, or touching

If the AFCI has sensed an arc, it's because insulation or isolation of the circuit isn't adequate. The problem or fault may be in one or a combination of these three conditions:

  • Line-to-ground fault

  • Line-to-neutral fault

  • Series arc in broken or separated conductor (could be a loose connection). Note that the branch/feeder AFCI won't generally detect a series arc because series current is usually below the detection level.

The following steps may be useful for getting to the root cause of the problem.

Step 1. Gather anecdotal information of any buzzing noises, visible arcing, the odor of smoke, or similar indications of improperly operating or defective appliances or equipment. This information may lead to the fault location. If arcing is suspected in an extension cord or a cord-connected appliance, immediately unplug the suspected unit.

Unplug all appliance and extension cords connected in the circuit. With the circuit de-energized, examine connections to the AFCI, receptacles, lighting fixtures, and other appliances. If tripping continues to occur when the AFCI is turned on, the fault is in the fixed wiring system. Move to Step 2.

Similarly, turn off all fixed appliances that have switches, such as lights and ceiling fans. It's important to note that since these circuits can't be fully disconnected (line, neutral, and ground), tripping that occurs when their switches are turned off doesn't necessarily mean that they're fault-free.

If the AFCI doesn't trip when all plugs are disconnected, turn on the AFCI again and reconnect the plugs one by one. Then one by one turn on fixed lights and appliances. This procedure may identify the faulted cord or appliance.

Because arcs are sometimes sporadic, turning off the circuit may temporarily clear the arc and it may not immediately reappear when the circuit is re-energized. For this reason, the arc may not be located by simply unplugging and reconnecting appliances.

Step 2. De-energize the load center by turning off the main disconnect. Try to do this before conducting the checks noted in Step 3. By means of a reliable voltmeter, verify that voltage isn't present.

Step 3. Apply the insulation resistance test described earlier to check for insulation adequacy line-to-neutral, line-to-ground, and neutral-to-ground. Alternatively, use an ohmmeter to check for electrical continuity line-to-neutral, line-to-ground, and neutral-to-ground. Continuity indicates the presence of a fault. The insulation resistance check is the preferred method of checking for a fault. Indication of adequate insulation in a circuit that has been identified as the location of an arc fault may point to a series fault, that is a broken conductor or a loose connection.

Once the fault is located, damage must be repaired or improperly operating equipment or appliances must be replaced.

In most cases, the previously mentioned steps will help locate the fault. It's important to recognize that the AFCI has provided an indication of a condition that could become a fire hazard. Don't continue to use the circuit without making a correction.

Arc detection technology for the reduction of fires is here to stay. The industry is only just beginning to understand the requirements and the devices available. However, the rules make good sense for circuit protection and can be followed with a basic understanding of Code language. The devices are similar to others that have been in use for a long time, namely circuit breakers and GFCIs. Proper installation hasn't proved to be an issue, and troubleshooting is a new skill to learn. However, with a systematic approach, even troubleshooting is achievable and can be mastered. The preceding information can support those who are using and applying these relatively new safety devices.

Gregory is the manager of industry standards-circuit protection for Schneider Elecric/Square D in Cedar Rapids, Iowa, and Manche is manager of industry codes for Schneider Electric/Square D in Lexington, Ky.

Sidebar: Shared Neutral Applications

Single-pole AFCIs can't protect circuits in which the neutral (grounded circuit) conductor is shared or mixed because current flowing out and returning is monitored for the presence of arcing faults. When single-pole AFCIs are applied, the circuit must have a distinct hot and a distinct neutral conductor. Otherwise, the AFCI can't distinguish arcing ground-fault occurrences. General availability of a 2-pole AFCI should be expected at some point in the near future since the technology is readily capable.

Contractors should understand that there are some drawbacks to using shared neutrals. For example, if a 2-pole, common-trip version of the AFCI is used, then both circuits are interrupted during a fault. If the 2-pole circuit breaker has independent trip, then when a circuit is tripped and an outlet device is removed (assuming a dead circuit), if the home run is split at that point, the wiring in the box isn't really dead.

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