Electrical firefighting: arc fault circuit breakers protect against 75% of electrical line fires

Abstract: This paper describes the role of new technologies arc fault circuit interrupter (AFCI), describes the knowledge of AFCI /.

I. Introduction

According to the 2009 statistics from the Ministry of Public Security Shenyang , 58.44% of major electrical fires were caused by faults in electrical lines and are increasing year by year. With the continuous development of society, the degree of electrification is getting higher and higher, and circuit protection is also increasing. The more important it is.

The fault arc in electrical energy is large, the temperature is high, the hazard is great, and it is very easy to cause fire. However, conventional circuit breakers can only protect against current leakage, overcurrent and short circuit. Many serious fire accidents are caused by arc faults below the rated current. Traditional circuit breakers cannot detect or prevent such failures. . Accidents caused by arc faults are increasingly convex

Obviously, we need to use AFCI technology to prevent and monitor the fire hazard of electrical lines.

Second, the general introduction of AFCI

What is AFCI

AFCI is the abbreviation of English Arc Fault Circuit Interrupt , can be translated as "Arc Fault Circuit Breaker", we all know, the traditional circuit breaker only protects against short-circuit and over-current, common leakage protection switch RCD ( GFCI ) only for "phase The "earth / ground" or "zero / ground" has a protective effect and cannot protect the fault arc between "phase / zero".

The AFCI technology is the latest circuit protection technology that can protect arc faults between “phase / zero” and “phase / ground” on the basis of conventional circuit breakers . These dangerous arcs may occur in electrical applications. On the wiring, plug and socket connection points, as well as on the wiring harness inside the household appliance or on the power cord of the appliance, etc., when a fault arc occurs, the arc can instantly generate a high temperature of approximately 4000 degrees, making it easy to ignite nearby flammable materials. , causing an electrical fire.

American Electrical Fire and AFCI Situation

In the United States, according to 1998 statistics CPSC (Consumer Product Safety commission CPSC), every year due to aging distribution lines cause a fire caused by arcing over 40,000 cases, resulting in US $ 1.68 billion in direct economic losses.

The National Fire Protection Administrator's National Association ( NASFM ) later investigated the cause of the electrical fire investigation report also pointed to “Fault Arc”, accounting for 83 % of the electrical fire .

Therefore, in order to effectively reduce electrical fires, the U.S. Electrical Code ( NEC2002 ) 210-12(A)(B) requires the installation of such AFCI circuit breakers and AFCI wall outlets in the bedrooms of new buildings and old buildings . All air conditioners must be installed with AFCI outlets. .

Because of the obvious effect after installation, NEC2008 increases the use of AFCI . ( 210 - 12 ( B )) almost all branch circuits require the installation of a fault arcing circuit breaker AFCI .

The National Fire Protection Association ( NFPA ) concluded in 2003 that the economics of the installation of AFCI : AFCI can prevent about 75 % -80 % of electrical line fires, NFPA estimated that the United States home-installed AFCI contains 20- year-old houses (per The average cost of living is $ 175 .) Costs incurred and casualties and property estimated to have occurred when a fire was not installed

Loss compared to the total society as a whole (1.9 one million homes nationwide) in the life of the AFCI (20--30 years) can save almost double the benefits of input costs, which is double the funds to save the country, and a huge The social benefits.

China's electrical fire situation

According to 2009 statistics of the Chinese Ministry of Public Security in Shenyang, 2003-- five years in 2007, each year the number of electrical fires accounted for the proportion of the total number of fires were: 23% 20.7% 21.9% 23.1% and 28.3%, of major electrical fire, 58.44% is caused by the failure of electrical lines and is increasing year by year. The form is rather severe.

According to statistics from relevant departments of the United States, China’s electrical fire is three times as many as the United States. The fire caused by the aging of the circuit accounts for the highest proportion of all fire accidents. The distribution of electrical circuits in our country is unreasonable, and there are many inferior electrical appliances and electrical fires are prone to occur. The voltage in our country is 220V, the voltage in the United States is 110V, and the high voltage is more prone to fault arcing. This is a hidden danger of electrical fire.

Third, electrical arc knowledge

Arc:

When the insulation of the electrical circuit is aged, damaged, the connector is connected with the virtual circuit, the circuit is connected with the virtual circuit, the fault arc will occur. (Arc discharge) The arc will occur even in the rated current range, and the arc will generate heat at the same time (more than 3000 degree)

Enough to ignite nearby combustibles.

Arcs on the line can be divided into two types, one is a normal operating arc, also known as "good arc", the other is a fault arc, called "bad arc."

1 , "good arc" refers to the arc generated by the rotation of the motor, such as electric drills, vacuum cleaners and so on. In addition, when people switch electrical appliances, the arc generated when plugging and unplugging electrical appliances is also "good arc."

2. The "Bad Arc" is a fault arc. The type of fault arc can basically be divided into three categories. Class A Class B and Class C. Class A is called a string arc, and Class B is a parallel arc. The figure is as follows:

Category C is the fault arc (earth leakage) between the live line and the neutral line. Since our electrical protection generally has a leakage protector, the Type C arc can be effectively prevented. (in case of good grounding)

3 , wires catch fire (0.5-1s)

US UL1699 Standard Introduction

UL1699 is the American standard that regulates AFCI . UL 1699 was developed in the early 1990s to identify home fires caused by arcs caused by overcurrents and short circuits. However, studies have found that a fault arc caused by a small current without sufficient overcurrent also has enough energy to cause a fire and cause a fire.

The UL1699 specification can be divided into three arc test methods: arc inspection test, misoperation test, and load start test. Initially , when UL1699 was drafted, the emphasis was on preventing the normal operation of loads (such as motors, lights, electronic control systems, etc.) from occurring when a non-erroneous arc occurred. Now with the application of the AFCI technology on household air conditioning power plugs, the AFCI technology must not only meet the safety regulations of UL1699 , but also meet the requirements of the air conditioning operating conditions (we call it product suitability), but now UL1699 There is no requirement for the applicability of the product, but it is very important in the actual use of the product.

According to the standard of UL1699, on the AC line, to identify AFCI "Arc good" and "bad Arc", when the AFCI perceived to 8 half arc fault "bad arc" signal in 0.5 seconds, the circuit breaker performs the trip, Disconnect the AC line in time.

Also in the "good arc" occurs, such as an electric drill, motor starters, not malfunction, now UL1699 2008 edition has been published.