Hi Ron Adobe PDF Document Start Arc Fault Circuit Interrupter (AFCI) FACT SHEET THE AFCI
The "AFCI" is an arc fault circuit interrupter. AFCIs are newly-developed electrical devices designed to protect against fires caused by arcing faults in the home electrical wiring. THE FIRE PROBLEM Annually, over 40,000 fires are attributed to home electrical wiring. These fires result in over 350 deaths and over 1,400 injuries each year 1 . Arcing faults are one of the major causes of these fires. When unwanted arcing occurs, it generates high temperatures that can ignite nearby combustibles such as wood, paper, and carpets. Arcing faults often occur in damaged or deteriorated wires and cords. Some causes of damaged and deteriorated wiring include puncturing of wire insulation from picture hanging or cable staples, poorly installed outlets or switches, cords caught in doors or under furniture, furniture pushed against plugs in an outlet, natural aging, and cord exposure to heat vents and sunlight. HOW THE AFCI WORKS Conventional circuit breakers only respond to overloads and short circuits; so they do not protect against arcing conditions that produce erratic current flow. An AFCI is selective so that normal arcs do not cause it to trip. The AFCI circuitry continuously monitors current flow through the AFCI. AFCIs use unique current sensing circuitry to discriminate between normal and unwanted arcing conditions. Once an unwanted arcing condition is detected, the control circuitry in the Ault, Singh, and Smith, " 1996 Residential Fire Loss Estimates", October 1998, U.S. Consumer Product Safety Commission, Directorate for Epidemiology and Health Sciences. AFCI trips the internal contacts, thus de-energizing the circuit and reducing the potential for a fire to occur. An AFCI should not trip during normal arcing conditions, which can occur when a switch is opened or a plug is pulled from a receptacle. Presently, AFCIs are designed into conventional circuit breakers combining traditional overload and short-circuit protection with arc fault protection. AFCI circuit breakers (AFCIs) have a test button and look similar to ground fault circuit interrupter (GFCI) circuit breakers. Some designs combine GFCI and AFCI protection. Additional AFCI design configurations are anticipated in the near future. It is important to note that AFCIs are designed to mitigate the effects of arcing faults but cannot eliminate them completely. In some cases, the initial arc may cause ignition prior to detection and circuit interruption by the AFCI. The AFCI circuit breaker serves a dual purpose - not only will it shut off electricity in the event of an "arcing fault", but it will also trip when a short circuit or an overload occurs. The AFCI circuit breaker provides protection for the branch circuit wiring and limited protection for power cords and extension cords. Single-pole, 15- and 20- ampere AFCI circuit breakers are presently available. WHERE AFCIs SHOULD BE USED The 1999 edition of the National Electrical Code, the model code for electrical wiring adopted by many local jurisdictions, requires AFCIs for receptacle outlets in bedrooms, effective January 1, 2002. Although the requirement is limited to only certain circuits in new residential construction, AFCIs should be considered for added protection in other circuits and for existing homes as well. Older homes with aging and deteriorating wiring systems can especially benefit from the added protection of AFCIs. AFCIs should also be considered whenever adding or upgrading a panel box while using existing branch circuit conductors. INSTALLING AFCIs AFCI circuit breakers should be installed by a qualified electrician. The installer should follow the instructions accompanying the device and the panel box. In homes equipped with conventional circuit breakers rather than fuses, an AFCI circuit breaker may be installed in the panel box in place of the conventional circuit breaker to add arc protection to a branch circuit. Homes with fuses are limited to receptacle or portable-type AFCIs, which are expected to be available in the near future, or AFCI circuit breakers can be added in separate panel boxes next to the fuse panel box. TESTING AN AFCI AFCIs should be tested after installation to make sure they are working properly and protecting the circuit. Subsequently, AFCIs should be tested once a month to make sure they are working properly and providing protection from fires initiated by arcing faults. A test button is located on the front of the device. The user should follow the instructions accompanying the device. If the device does not trip when tested, the AFCI is defective and should be replaced. AFCIs vs. GFCIs The AFCI should not be confused with the GFCI or ground fault circuit interrupter. The GFCI is designed to protect people from severe or fatal electric shocks while the AFCI protects against fires caused by arcing faults. The GFCI also can protect against some electrical fires by detecting arcing and other faults to ground but cannot detect hazardous across-the-line arcing faults that can cause fires. A ground fault is an unintentional electric path diverting current to ground. Ground faults occur when current leaks from a circuit. How the current leaks is very important. If a person's body provides a path to ground for this leakage, the person could be injured, burned, severely shocked, or electrocuted. The National Electrical Code requires GFCI protection for receptacles located outdoors; in bathrooms, garages, kitchens, crawl spaces and unfinished basements; and at certain locations such as near swimming pools. A combination AFCI and GFCI can be used to satisfy the NEC requirement for GFCI protection only if specifically marked as a combination device. Drag Page Menu 8.5 x 11 in Status Bookmarks Single Page Continuous Continuous - Facing Facing Zoom Out Zoom In Next Page Last Page File Save a Copy Print Email Search Basic Hand Tool Select Snapshot Tool Select Select Zoom ZoomIn Actual Size Fit Page Fit Width Zoom Out Zoom Menu Zoom In Edit Rotate View Rotate Clockwise Rotate Clockwise Tasks Add-on Tools Adobe PDF Document End -----Original Message----- From: blindhandyman@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of R & S Enterprises Sent: Monday, 31 July 2006 10:28 To: blindhandyman@yahoogroups.com Subject: Re: [BlindHandyMan] Ground Fault Circuit Interrupter Hey Ray, Good posting on ground fault interrupters. Maybe you could find something on arc fault interrupters. In the last few years they have become a new code requirement for protecting outlets in sleeping areas. Last time I cheched some time ago information was pretty sketchy on how they worked. Thanks, Ron ----- Original Message ----- From: "Ray Boyce" <[EMAIL PROTECTED]> To: <blindhandyman@yahoogroups.com> Sent: Sunday, July 30, 2006 11:11 PM Subject: [BlindHandyMan] Ground Fault Circuit Interrupter > Hi > What is a GFCI? > > A Ground Fault Circuit Interrupter (GFCI) is a device to protect against > electric shock should someone come in contact with a live (Hot) wire and > a path to ground which would result in a current through his/her body. The > GFCI operates by sensing the difference between the currents in the Hot and > Neutral conductors. Under normal conditions, these should be equal. > However, > if someone touches the Hot and a Ground such as a plumbing fixture or > they are standing in water, these currents will not be equal as the path is > to Ground - a ground fault - and not to the Neutral. This might occur > if a short circuit developed inside an ungrounded appliance or if someone > was working on a live circuit and accidentally touched a live wire. > > The GFCI will trip in a fraction of a second at currents (a few mA) well > below those that are considered dangerous. Note that a GFCI is NOT a > substitute for a fuse or circuit breaker as these devices are still > required to protect equipment and property from overloads or short > circuits that can result in fire or other damage. > > GFCIs can be installed in place of ordinary outlets in which case they > protect that outlet as well as any downstream from it. There are also > GFCIs that install in the main service panel. > > Note that it may be safe and legal to install a GFCI rated at 15 A on a > 20 A circuit since it will have a 20 A feed-through. Of course, the GFCI > outlet itself can then only be used for appliances rated 15 A or less. > > Many (if not most) GFCIs also test for a grounded neutral condition where a > low resistance path exists downstream between the N and G conductors. If > such > a situation exists, the GFCI will trip immediately when power is applied > even > with nothing connected to the protected outlets. > > GFCIs, overloads, and fire safety > > A GFCI is NOT a substitute for a fuse or circuit breaker (unless it is a > combined unit - available to replace circuit breakers at the service panel). > > Therefore, advice like "use a GFCI in place of the normal outlet to prevent > appliance fires" is not really valid. > > There may be some benefit if a fault developed between Hot and Ground but > that > should blow a fuse or trip a circuit breaker if the outlet is properly > wired. > If the outlet is ungrounded, nothing would happen until someone touched the > metal cabinet and an earth ground simultaneously in which case the GFCI > would > trip and provide its safety function. See the section: " > Why a GFCI should not > be used with major appliances" > for reasons why this is not generally > desirable as long as the appliance or outlet is properly grounded. > > However, if a fault occurs between Hot and Neutral - a short in the motor, > for > example - a GFCI will be perfectly happy passing almost any sort of overload > current until the GFCI, wiring, and appliance melts down or burns up - a > GFCI > is not designed to be a fuse or circuit breaker! That function must be > provided separately. > > How does a GFCI work > > GFCIs typically test for the following condition: > > 1. A Hot to Ground (safety/earth) fault. Current flows from the Hot wire to > Ground bypassing the Neutral. This is the test that is most critical for > safety. > > 2. A grounded neutral fault. Due to miswiring or a short circuit, the N and > G > wires are connected by a low resistance path downstream of the GFCI. In > this case, the GFCI will trip as soon as power is applied even if nothing > is connected to its protected (load) circuit. > > To detect a Hot to Ground fault, both current carrying wires pass through > the > core of a sense coil (transformer). When the currents are equal and > opposite, > there is no output from its multiturn sense voltage winding. When an > imbalance > occurs, an output signal is produced. When this exceeds a threshold, a > circuit > breaker inside the GFCI is tripped. > > GFCIs for 220 VAC applications need to monitor both Hots as well as the > Neutral. The principles are basically the same: the sum of the currents in > Hot1 + Hot2 + Neutral should be zero unless a fault exists. > > To detect a grounded neutral fault, a separate drive coil is continuously > energized and injects a small 120 Hz signal into the current carrying > conductors. If a low resistance path exists between N and G downstream > of the GFCI, this completes a loop (in conjunction with the normal > connection > between N and G at the service panel) and enough current flows to again > trip the GFCI's internal circuit breaker. > > GFCIs use toroidal coils (actually transformers to be more accurate) where > the > core is shaped like a ring (i.e., toroid or doughnut). These are convenient > and efficient for certain applications. For all practical purposes, they > are > just another kind of transformer. If you look inside a GFCI, you will find > a > pair of toroidal transformers (one for H-N faults and the other for N-G > faults > as described above). They look like 1/2" diameter rings with the main > current > carrying conductors passing once through the center and many fine turns of > wire (the sense or drive winding) wound around the toroid. > > All in all, quite clever technology. The active component in the Leviton > GFCI is a single chip - probably a National Semiconductor LM1851 Ground > Fault > Interrupter. For more info, check out the specs at National'a web site at: > http://www.national.com/pf/LM/LM1851.html. > > > More on how the GFCI detects a N-G short > > To detect a Neutral to Ground fault there is a second transformer placed > upstream of the H-G sense transformer (see the illustration of the internal > circuitry of the GFCI at: > http://www.national.com/pf/LM/LM1851.html). > A small > drive signal is continuously injected via the 200 T winding which induces > equal voltages on the H and N wires passing through its core. > > * If N and G are separate downstream (as they should be), no current will be > flow in either wire and the GFCI will not trip. (No current will flow in > the H wire as a result of this stimulus because the voltage induced on both > H and N is equal and cancels.) > > * If there is a N-G short downstream, a current will flow through the N > wire, > to the G wire via the short, and back to the N wire via the normal N-G > connection at the service panel. Since there will be NO similar current in > the H wire, this represents a current unbalance and will trip the GFCI in > the same manner as the usual H-G short. > > * Interestingly, this scheme automatically detects a H-H fault as well. > This > unlikely situation could occur if the Hots from two separate branch circuits > were accidentally tied together in a junction box downstream of the GFCI. > It works the same way except that the unbalance in current that trips the > GFCI flows through the H wire, through the H-H fault, and back around via > the Hot busbar at the service panel. Of course if the two Hots are not on > the same phase, there may be fireworks as well :-). > > GFCIs and safety ground > > Despite the fact that a Ground Fault Circuit Interrupter (GFCI) may be > installed in a 2 wire circuit, the GFCI does not create a safety ground. > In fact, shorting between the Hot and Ground holes in the GFCI outlet > will do absolutely nothing if the GFCI is not connected to a grounded > circuit (at least for the typical GFCI made by Leviton sold at hardware > stores and home centers). It will trip only if a fault occurs such that > current flows to a true ground. If the original circuit did not have a > safety ground, the third hole is not connected. What this means is that > an appliance with a 3 prong plug can develop a short between Hot and the > (supposedly) grounded case but the GFCI will not trip until someone > touches the case and an earth ground (e.g., water pipe, ground from > some other circuit, etc.) at the same time. > > Note that even though this is acceptable by the NEC, I do not consider it > desirable. Your safety now depends on the proper functioning of the GFCI > which is considerable more complex and failure prone than a simple fuse or > circuit breaker. Therefore, if at all possible, provide a proper Code > compliant ground connection to all outlets feeding appliances with 3 wire > plugs. > > Where are 3 wire grounded outlets required? > > If you move into a house or apartment where some or all of the outlets are > the > old 2 prong ungrounded type, don't panic. There is no reason to call an > electrician at 2:00 AM in the morning to upgrade them all at great expense. > > You don't need grounded outlets for two wire appliances, lamps, etc. They > do essentially nothing if the third hole isn't occupied :-). A GFCI will > provide much more protection! > > You should have grounded outlets for the following: > > * Computers in order for the line filters and surge suppressors to be most > effective. > > * High-end entertainment gear if it uses 3 prong plugs for similar reasons. > > * Microwave ovens. For safety, these really should be on a grounded > circuit. > (A GFCI will not protect against a fault on the high voltage side of a > microwave oven, though this sort of fault is extremely unlikely). > > * Large appliances including refrigerators, clothes washers and dryers, > dehumidifiers, window air conditioners, etc. > > In most cases, there will only be a few circuits where this is needed and > only > these need to be upgraded. To what extent the wiring plan of your residence > separates lighting type circuits from those with outlets that will be used > for > 3 wire equipment will determine how easy it is to upgrade only those outlets > that are affected. It may be cheaper to just add new branch circuits for > specific equipment needs. > > > > To listen to the show archives go to link > http://acbradio.org/handyman.html > or > ftp://ftp.acbradio.org/acbradio-archives/handyman/ > > The Pod Cast address for the Blind Handy Man Show is. > http://www.acbradio.org/news/xml/podcast.php?pgm=saturday > > The Pod Cast address for the Cooking In The Dark Show is. > http://www.gcast.com/u/cookingindark/main.xml > > Visit The New Blind Handy Man Files Page To Review Contributions From Various List Members At The Following Address: > http://www.jaws-users.com/handyman/ > Visit the new archives page at the following address > http://www.mail-archive.com/blindhandyman@yahoogroups.com/ > For a complete list of email commands pertaining to the Blind Handy Man list just send a blank message to: > [EMAIL PROTECTED] > Yahoo! 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