AFCI’s, cost, and fire-safety

Apr 15, 2011   //   by Robert Monk   //   New in electricity..., Reasons to do electrical right  //  3 Comments
New-wired residences will tend to have at least (4) AFCI breakers.

New-wired residences will tend to have at least (4) AFCI breakers.

Arc Fault Circuit Interrupting breakers (AFCIs) turn off circuits when they detect the electronic signature of the types of arcing in a circuit that could ignite combustible material. They have played an increasing role in residential fire safety through automatic electrical power circuit monitoring and disconnect since municipalities throughout the United States and beyond adopted the 2005 edition of the National Fire Protection Association’s “National Electrical Code”, aka NEC 2005. Subsequent editions of the NEC have mandated expanded application of AFCI technology throughout homes. I like to say, as a rule of thumb, “If the NEC does not require GFCI protection (such as in bathrooms, kitchens, and outdoors), then AFCI protection is required.” Although the relative cost of standard and AFCI breakers is very high ($32 to $45 per circuit for AFCI protected vs. $2 to $7 for standard overcurrent protection circuit breakers), I believe they are worth the money if only as an added quality control step that forces installers to remedy latent circuit faults that could otherwise go undetected. Moreover, AFCI breaker costs have been dropping (very slowly) as demand increases with implementation of the new NEC Code requirements, and both breaker and load center manufacturers continue to innovate to improve the efficiency and quality of installations that incorporate AFCI type breakers.

An excellent video on YouTube details the function, costs, and fire-prevention advantages of Arc Fault Circuit Interrupters (AFCI’s, AFCI breakers). These advanced electronic devices monitor current fluctuations on both conductors of the 120V AC circuit (standard breakers provide only a simple current limit, and only on one conductor). In addition to the standard feature of absolute and time-dependent limits on current in the circuit, AFCI circuit breakers also ‘look’ for patterns of instantaneous spikes in current characteristic of intermittent arcing faults, typical in frayed extension cords, loose sockets, and wiring damaged inside a wall.

Safety and Quality Control Functions of AFCI circuit protection

Although required only in residences, for newly installed circuits or when installing new extensions of existing circuits, AFCI technology may be best suited for older wiring and/or older buildings, where residents are more likely to be tempted/forced to overload circuits and/or use extension cords. Older houses have fewer convenience receptacles — usually one or two per room, rather than three or four or five. More plug-end connections with extension cords; likelihood someone will run a cord under a highly-trafficked rug and let it wear and fray, without inspection, over a period of years; connecting a cord-end poorly behind a bed because no other options exist; looseness and grounding problems or polarity problems typical at aged receptacles: all these old-house issues increase the chances for, and potential danger from, an arcing fault. Insurance companies would do well to offer homeowners a discount for AFCI-protecting existing circuits not covered in the National Electrical Code.

 

Industry response to installation logistics of AFCI breakers

For all their many advantages, AFCI breakers do incorporate a rather clumsy workaround for allowing them to integrate with legacy breaker panels (load centers). A coiled ‘pig tail’ conductor jumpers from the breaker to the grounded or ‘neutral’ terminal bus bar in the load center, filling up the empty area beside breaker terminals (‘gutter’) that normally accommodates phase ‘hot’ conductors — and can sometimes become overcrowded, especially when adding AFCI pig tails. Manufacturers have begun to respond by offering load centers featuring integrated AFCI-friendly neutral busses that permit the breaker to make a direct connection to the neutral bus, rather than fill up the load center gutter with workaround ‘pig tail’ conductor.

SquareD AFCI-friendly load center retail display

Manufacturers have begun to accommodate AFCIs using enhanced methods over the ‘pig-tail’ workaround characteristic of 1st and 2nd-generation AFCI breakers.



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3 Comments

  • A great feature of AFCI breakers for electricians is the ability to remotely de-energize an AFCI-breakered circuit by crossing the neutral (grounded conductor) wire with the equipment (safety) grounding wire. The breaker will usually detect this ground fault and trip off. This method is low-impact as compared to direct-shorting neutral-hot (grounded and phase conductors in 120V branch circuit wiring), which can damage wire ends at the short, and electronic components installed elsewhere in the circuit, such as $50 dimmers and pricey high-efficiency lamps and fixtures. The ground fault is low-energy and operates the AFCI trip much like a relay switch.

    NOTE, though, that crossing grounding and neutral wires won’t always trip an AFCI. I suspect that the operation depends on resistance between the crossed location and breaker (more distance/resistance reduces the fault current detected at the breaker), and also possibly whether any loads are connected on the circuit when the wires cross (is there any current flowing to move through the wiring fault?).

  • [...] AFCI breakers are so sensitive that I often hear of electrician complaints that they may be giving false alarms. However, I have installed more than 100 of them and only ever encountered one – maybe – that may have been tripping improperly. I’m not sure I could report as good a record for standard breakers, which whose failure rate I’ve not monitored as closely (they cost 1/5 as much, for one thing). [...]

  • [...] AFCI Protection for existing circuits. Required for all dwelling areas since 2010 in Philadelphia, Arc Fault Circuit Interrupters may be most useful for preventing fires when applied to old circuits: pre-existing wiring. The AFCI breaker costs $40 (vs. $5 for a comparable standard breaker). Note that the highly-sensitive electronics in these circuit breakers may reveal defects in extension cords or appliances (usually their cords), that have remained latent prior to AFCI installation. This can be inconvenient, at first, but identifying these defects before they spark a fire can only be good. [...]

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